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<journal-id journal-id-type="publisher-id">Front. Phys.</journal-id>
<journal-title>Frontiers in Physics</journal-title>
<abbrev-journal-title abbrev-type="pubmed">Front. Phys.</abbrev-journal-title>
<issn pub-type="epub">2296-424X</issn>
<publisher>
<publisher-name>Frontiers Media S.A.</publisher-name>
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<article-id pub-id-type="publisher-id">1522170</article-id>
<article-id pub-id-type="doi">10.3389/fphy.2025.1522170</article-id>
<article-categories>
<subj-group subj-group-type="heading">
<subject>Physics</subject>
<subj-group>
<subject>Original Research</subject>
</subj-group>
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</article-categories>
<title-group>
<article-title>Efficient and secure electronic evidence exchange scheme for internet of things</article-title>
<alt-title alt-title-type="left-running-head">Xiao and Chen</alt-title>
<alt-title alt-title-type="right-running-head">
<ext-link ext-link-type="uri" xlink:href="https://doi.org/10.3389/fphy.2025.1522170">10.3389/fphy.2025.1522170</ext-link>
</alt-title>
</title-group>
<contrib-group>
<contrib contrib-type="author">
<name>
<surname>Xiao</surname>
<given-names>Yulong</given-names>
</name>
<uri xlink:href="https://loop.frontiersin.org/people/2882567/overview"/>
<role content-type="https://credit.niso.org/contributor-roles/conceptualization/"/>
<role content-type="https://credit.niso.org/contributor-roles/data-curation/"/>
<role content-type="https://credit.niso.org/contributor-roles/formal-analysis/"/>
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<role content-type="https://credit.niso.org/contributor-roles/methodology/"/>
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<role content-type="https://credit.niso.org/contributor-roles/Writing - review &#x26; editing/"/>
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<contrib contrib-type="author" corresp="yes">
<name>
<surname>Chen</surname>
<given-names>Liang</given-names>
</name>
<xref ref-type="corresp" rid="c001">&#x2a;</xref>
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</contrib-group>
<aff>
<institution>College of Criminal Investigation</institution>, <institution>People&#x2019;s Public Security University of China</institution>, <addr-line>Beijing</addr-line>, <country>China</country>
</aff>
<author-notes>
<fn fn-type="edited-by">
<p>
<bold>Edited by:</bold> <ext-link ext-link-type="uri" xlink:href="https://loop.frontiersin.org/people/797979/overview">Hui-Jia Li</ext-link>, Nankai University, China</p>
</fn>
<fn fn-type="edited-by">
<p>
<bold>Reviewed by:</bold> <ext-link ext-link-type="uri" xlink:href="https://loop.frontiersin.org/people/617652/overview">Jinlong Ma</ext-link>, Hebei University of Science and Technology, China</p>
<p>
<ext-link ext-link-type="uri" xlink:href="https://loop.frontiersin.org/people/2657929/overview">Ge Gao</ext-link>, Beijing Sport University, China</p>
</fn>
<corresp id="c001">&#x2a;Correspondence: Liang Chen, <email>20051224@ppsuc.edu.cn</email>
</corresp>
</author-notes>
<pub-date pub-type="epub">
<day>27</day>
<month>01</month>
<year>2025</year>
</pub-date>
<pub-date pub-type="collection">
<year>2025</year>
</pub-date>
<volume>13</volume>
<elocation-id>1522170</elocation-id>
<history>
<date date-type="received">
<day>04</day>
<month>11</month>
<year>2024</year>
</date>
<date date-type="accepted">
<day>03</day>
<month>01</month>
<year>2025</year>
</date>
</history>
<permissions>
<copyright-statement>Copyright &#xa9; 2025 Xiao and Chen.</copyright-statement>
<copyright-year>2025</copyright-year>
<copyright-holder>Xiao and Chen</copyright-holder>
<license xlink:href="http://creativecommons.org/licenses/by/4.0/">
<p>This is an open-access article distributed under the terms of the Creative Commons Attribution License (CC BY). The use, distribution or reproduction in other forums is permitted, provided the original author(s) and the copyright owner(s) are credited and that the original publication in this journal is cited, in accordance with accepted academic practice. No use, distribution or reproduction is permitted which does not comply with these terms.</p>
</license>
</permissions>
<abstract>
<p>With the rapid development of information technology, Internet of Things (IoT) is profoundly impacting various fields of the socio-economic landscape, driving the transformation of traditional industries towards intelligence. However, the widespread application of IoT has also led to a surge in electronic evidence, whose importance in the judicial field is increasingly prominent, but its characteristics such as ease of replication and leakage have posed new challenges for privacy protection. This paper focuses on the security and privacy issues of electronic evidence in IoT and proposes an efficient and secure interaction scheme based on chebyshev chaotic map, hash functions and XOR operations. Through a secure two-factor authentication mechanism, this scheme achieves identity verification between the user and the storage center, as well as confidentiality during the data transmission process. This has significant implications for the healthy development of IoT, judicial fairness and personal privacy protection. Experimental and theoretical analysis shows that the proposed scheme not only effectively resists various known attacks, but also performs excellently in terms of communication and computation costs, making it well-suited for IoT.</p>
</abstract>
<kwd-group>
<kwd>internet of things</kwd>
<kwd>electronic evidence</kwd>
<kwd>privacy protection</kwd>
<kwd>authentication</kwd>
<kwd>security</kwd>
</kwd-group>
<custom-meta-wrap>
<custom-meta>
<meta-name>section-at-acceptance</meta-name>
<meta-value>Social Physics</meta-value>
</custom-meta>
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</article-meta>
</front>
<body>
<sec id="s1">
<title>Highlights</title>
<p>&#x2022; A secure authentication scheme is designed for electronic evidence transmission in IoT.</p>
<p>&#x2022; Security analysis shows that the scheme provides enhanced security.</p>
<p>&#x2022; The scheme exhibits higher computational efficiency and lower overhead.</p>
</sec>
<sec id="s2">
<title>1 Introduction</title>
<p>In recent years, Internet of Things (IoT) has become an important driving force for the development of modern science and technology [<xref ref-type="bibr" rid="B1">1</xref>]. IoT integrates various information sensing devices with the Internet through intelligent sensing, identification technologies, and pervasive computing, forming a vast network that connects objects, thereby enabling efficient information exchange between people and objects, as well as between objects themselves [<xref ref-type="bibr" rid="B2">2</xref>]. However, with the widespread adoption of IoT applications, the volume of electronic evidence generated has also grown exponentially. The vast amount of electronic evidence data is increasingly valuable and useful [<xref ref-type="bibr" rid="B3">3</xref>]. In the judicial field, electronic data has increasingly been used in recent years as a new form of evidence to prove the facts of a case. The concept of electronic evidence has emerged, and the perception of judicial proof is gradually changing [<xref ref-type="bibr" rid="B4">4</xref>]. Electronic evidence, which is generated by the application of electronic information technology and can be used to prove case facts, includes electronic materials and their derivatives. Due to its characteristics of easy collection, convenient preservation, efficient transmission, and small space requirements, electronic evidence has gradually gained importance in the judiciary and, in many cases, carries the same legal weight as traditional evidence [<xref ref-type="bibr" rid="B5">5</xref>]. The extensive use of electronic evidence in the digitization of the legal system has gradually revealed its inherent flaws and limitations, which are becoming increasingly influential. First, electronic evidence can appear in multimedia forms such as text, images, audio, and video, which places higher demands on storage, extraction, and identification methods. Additionally, electronic evidence exists in the non-continuous form of binary code, and its transmission and storage rely on computer technology and specialized equipment. Non-experts find it difficult to identify and examine such evidence. If the transmission medium or storage device is compromised, the integrity of the electronic evidence may be altered, resulting in a loss of evidentiary value. Finally, in all stages of electronic evidence collection, identification, storage, and application, it is susceptible to tampering due to computer errors, virus attacks, or deliberate technical manipulation. This process is difficult to detect or trace, which directly compromises the authenticity of the electronic evidence [<xref ref-type="bibr" rid="B6">6</xref>&#x2013;<xref ref-type="bibr" rid="B9">9</xref>].</p>
<p>Meanwhile, the privacy issues related to electronic evidence are receiving increasing attention. As electronic evidence, in its digital form, is easily replicated, accessed, and leaked, it often contains private information of states, enterprises, and individuals, whose disclosure would lead to privacy security issues [<xref ref-type="bibr" rid="B10">10</xref>&#x2013;<xref ref-type="bibr" rid="B12">12</xref>]. The privacy issues associated with electronic evidence are of significant importance to both the state and the general public.</p>
<p>On the other hand, since electronic evidence is a form of electronic data, its transmission, download, and upload processes are easily executed. However, the flow of this data is difficult to record, making it challenging to trace the entities involved and the sequence of its transfer. Critical information such as the entity handling the electronic evidence and the time of operation is often unobtainable. Once a privacy breach occurs during the transfer of electronic evidence, it becomes difficult to trace the specific stage at which the breach happened, complicating accountability and posing significant challenges to privacy protection [<xref ref-type="bibr" rid="B13">13</xref>&#x2013;<xref ref-type="bibr" rid="B15">15</xref>]. In this context, it is crucial to implement identity verification between users and storage centers while ensuring secure communication between nodes. A feasible security solution is to deploy an authenticated key agreement scheme, which verifies the true identity of communicating entities before sharing any sensitive information over unsecured wireless channels [<xref ref-type="bibr" rid="B16">16</xref>&#x2013;<xref ref-type="bibr" rid="B18">18</xref>]. Mutual authentication can be used to verify the true identity of communication participants before transmitting data, eliminating the need to send sensitive information over unsecured channels. After participants have mutually confirmed their identities, the AKA scheme can negotiate a shared session key to encrypt subsequent transmission messages. Therefore, users and storage centers can authenticate each other, allowing only users with the session key to access the collected electronic evidence, while unauthorized users cannot. Researching efficient and secure interaction schemes for electronic evidence in IoT is of great significance for promoting the healthy development of IoT technology, upholding judicial fairness, and protecting personal privacy. Therefore, this paper proposes an efficient and secure interaction scheme for electronic evidence in the IoT. This scheme achieves rapid authentication of entity identity and ensures confidentiality during data transmission. This scheme not only has provable security and can resist various mentioned attacks, but it is also suitable for IoT environments with limited resources and energy, offering lower computational and communication overhead. Our contributions are as follows:<list list-type="simple">
<list-item>
<p>(1) A secure two-factor authentication scheme is designed for the security of electronic evidence transmission in IoT. The scheme employs a pseudonym mechanism, hiding the pseudonym within the transmission message to achieve user identity anonymity and ensure identity security. Additionally, chebyshev chaotic map, hash functions and XOR operations are utilized to complete identity authentication between users and storage centers, achieving strong authentication security and scalability.</p>
</list-item>
<list-item>
<p>(2) The proposed scheme satisfies security under formal proof, also meeting mutual authentication security and key agreement security. Informal security analysis shows that the scheme provides enhanced security, and resists various known attacks such as man-in-the-middle attacks and impersonation attacks.</p>
</list-item>
<list-item>
<p>(3) In terms of costs, the scheme exhibits higher computational efficiency and lower overhead compared to other schemes.</p>
</list-item>
</list>
</p>
<p>The organization of the rest is as follows. A comprehensive summary of existing researches in the relevant field are conducted in <xref ref-type="sec" rid="s2">Section 2</xref>. In <xref ref-type="sec" rid="s3">Sections 3</xref>, <xref ref-type="sec" rid="s4">4</xref>, the fundamental theoretical framework supporting the proposed scheme is thoroughly explained and the specific details of the scheme are introduced. In <xref ref-type="sec" rid="s5">Section 5</xref>, we conducted the proposed scheme. <xref ref-type="sec" rid="s6">Section 6</xref> presents the performance experiments. <xref ref-type="sec" rid="s7">Section 7</xref> concludes the paper.</p>
</sec>
<sec id="s3">
<title>2 Related work</title>
<p>Identity authentication is one of the most crucial components in IoT systems, especially in wireless networks, where it is indispensable. This function prevents security issues such as data theft and identity spoofing. Many researchers have proposed their own security schemes for IoT identity authentication. <xref ref-type="table" rid="T1">Table 1</xref> shows a comparative analysis of relevant protocols.</p>
<table-wrap id="T1" position="float">
<label>TABLE 1</label>
<caption>
<p>Comparative analysis.</p>
</caption>
<table>
<thead valign="top">
<tr>
<th align="center">Protocol</th>
<th align="left">Limitation</th>
</tr>
</thead>
<tbody valign="top">
<tr>
<td align="left">Sandeep et al. [<xref ref-type="bibr" rid="B19">19</xref>]</td>
<td align="left">Impersonation attacks and stolen smart card attacks</td>
</tr>
<tr>
<td align="left">Butun et al. [<xref ref-type="bibr" rid="B20">20</xref>]</td>
<td align="left">Excessive computational overhead</td>
</tr>
<tr>
<td align="left">Shen et al. [<xref ref-type="bibr" rid="B22">22</xref>]</td>
<td align="left">Significant computational overhead and replay attacks</td>
</tr>
<tr>
<td align="left">Zheng et al. [<xref ref-type="bibr" rid="B26">26</xref>]</td>
<td align="left">The computational complexity of key calculations on the user side is too high</td>
</tr>
<tr>
<td align="left">Lin et al. [<xref ref-type="bibr" rid="B28">28</xref>]</td>
<td align="left">the packet loss rate in this scheme significantly increases</td>
</tr>
<tr>
<td align="left">Sanaz et al. [<xref ref-type="bibr" rid="B30">30</xref>]</td>
<td align="left">Significant computational overhead</td>
</tr>
<tr>
<td align="left">Song et al. [<xref ref-type="bibr" rid="B32">32</xref>]</td>
<td align="left">Transmission round number desynchronization</td>
</tr>
<tr>
<td align="left">Rathore et al. [<xref ref-type="bibr" rid="B34">34</xref>]</td>
<td align="left">High computational overhead</td>
</tr>
<tr>
<td align="left">Hui et al. [<xref ref-type="bibr" rid="B35">35</xref>]</td>
<td align="left">Ciphertext analysis attacks</td>
</tr>
</tbody>
</table>
</table-wrap>
<p>Sandeep et al. [<xref ref-type="bibr" rid="B19">19</xref>] presented a protocol for multi-server architectures. However, it fails to resist impersonation attacks and stolen smart card attacks. Butun et al. [<xref ref-type="bibr" rid="B20">20</xref>] designed a cloud-centric multi-layer framework. The entities included users, wearable devices, wearable device network coordinators and cloud service providers. It then provided multi-level authentication, such as authentication between users and cloud service providers, between cloud service providers and wearable device network coordinators and between wearable network coordinators and wearable devices. The scheme used the digital signature and identity authentication between cloud service providers and users. The algorithm is used during the initialization phase for negotiating the key for the message authentication code algorithm between different entities. The algorithm was used to compute the hash authentication code of data packets between entities. The extensive use of digital certificate signature algorithms and multi-tier key agreement algorithms in this scheme results in excessive computational overhead. Furthermore, the identity authentication method relied on an authentication chain, which, if disrupted at any stage, can cause the entire authentication process to fail. Ramos et al. [<xref ref-type="bibr" rid="B21">21</xref>] proposed a method for point and field algorithms, designed to implement access control mechanisms based on security and functionality in smart objects. Shen et al. [<xref ref-type="bibr" rid="B22">22</xref>] focused on efficient multi-layer authentication protocols. First, the authors proposed a group protocol. Then, the authors proposed a certificate-less authentication protocol between the personal digital assistant and application providers. In these protocols, elliptic encryption algorithms offer low computational overhead and high security. However, the excessive use of point multiplication calculations in this scheme introduces significant computational overhead. Additionally, the lack of consideration for timestamps in each data packet transmission makes it vulnerable to replay attacks. Shen et al. [<xref ref-type="bibr" rid="B23">23</xref>] described a lightweight and cloud-assisted protocol. During the registration phase, the user and the central server send the hash value of their device ID to the network administrator, who then uses an elliptic curve algorithm to select a random number to compute the public key for the corresponding entity. The network administrator also provides a signature value using their private key and the corresponding ID&#x2019;s hash value to the entity. This achieves entity identity authentication while protecting the entity&#x2019;s ID from being disclosed, thus enabling secure anonymous authentication in the protocol. However, the scheme&#x2019;s use of multiple signature algorithms increases computational overhead and fails to resist replay attacks. Gope et al. [<xref ref-type="bibr" rid="B24">24</xref>] described a lightweight real-time protocol for anonymous identity verification. It guarantees anonymity and ensures both forward and backward data confidentiality. However, it uses an excessive number of hash functions, making its authentication more susceptible to attacks compared to other methods. Similarly, Chifor et al. [<xref ref-type="bibr" rid="B25">25</xref>] proposed a scheme. The scheme utilizes the existing mobile authentication framework to achieve fast and convenient entity identity verification. However, this scheme simply leverages an existing open-source framework and its corresponding APIs for specific user authentication and authorization, rather than being a genuinely lightweight solution.</p>
<p>Encrypting transmitted data using a secure shared key is an effective method for establishing a secure communication channel. The secure distribution of the shared key is crucial, and key agreement is an effective way to address key distribution. However, as the sensor devices in IoT rapidly increases on a large scale, it presents greater challenges for secure transmission in the IoT context. Zheng et al. [<xref ref-type="bibr" rid="B26">26</xref>] presented a group key management scheme, which has the advantage of minimizing parameter broadcasts. However, the computational complexity of key calculations on the user side is too high. In the same year, Guo et al. [<xref ref-type="bibr" rid="B27">27</xref>] presented a secure data scheme. In this scheme, a single public key is linked to multiple groups of private keys, making it easy for attackers to identify the group sending the message but difficult to trace the sender&#x2019;s specific message. Lin et al. [<xref ref-type="bibr" rid="B28">28</xref>] presented a scheme based on ordered message authentication. In this scheme, a vehicle first sends a hash chain to nearby vehicles, which then generate message authentication codes based on elements of the hash chain. Nearby vehicles can use this information to authenticate the sender. However, due to the need for the sender to frequently broadcast its hash chain in large-scale networks, the packet loss rate in this scheme significantly increases. In recent years, the transmission efficiency and security of devices in the IoT environment have garnered widespread attention. Vijayakumar et al. [<xref ref-type="bibr" rid="B29">29</xref>] proposed a data security transmission protocol. The protocol used bidirectional authentication to ensure identity verification and employed a group key algorithm for key agreement. However, this scheme required re-negotiating the group key every time a user joins or leaves, which incurs a certain computation overhead on the secure transmission of the entire model. Sanaz et al. [<xref ref-type="bibr" rid="B30">30</xref>] presented a scheme within the context of mobile smart healthcare networks. This scheme achieved secure and efficient identity authentication and authorization for end users. It incorporates a key renegotiation mechanism, which reuses previous parameters to save on the cost of parameter negotiation, while the cross-regional transition mechanism effectively addresses the issue of patient identity authentication during spatial movements. However, because it is a traditional communication protocol that uses certificate mechanisms for identity authentication, it results in significant computational overhead, making it unsuitable for smart home environments. Tarun et al. [<xref ref-type="bibr" rid="B31">31</xref>] demonstrated through capability and performance analysis that ECDH is more suitable for IoT. The authors tested the time required for ECDH and RSA encryption and decryption using specific code, and conducted detailed energy consumption analyses using industry-standard test suites. They also made precise comparisons with other algorithms and ultimately applied the ECDH scheme to image encryption. Song et al. [<xref ref-type="bibr" rid="B32">32</xref>] described an improved protocol for IoT devices. This protocol employs a dual-key encryption mechanism, with one key used for plaintext encryption and another for computing MAC. The shared encryption key and MAC key are generated by a chaotic logistic map system. Instead of using a device authentication code mechanism for identity authentication, this scheme relies on a simple MAC-based approach. The mechanism adopted in this scheme is a one-time pad, where each data encryption is accompanied by a transmission round number. Although a one-time pad significantly enhances data security, it also introduces the problem of transmission round number desynchronization, leading to decryption confusion in the smart home transmission scheme, which could be a critical issue. Shen et al. [<xref ref-type="bibr" rid="B33">33</xref>] focused on secure data uploading. They proposed an improved scheme, which ensured the integrity of cloud-verified data while preventing data theft and modification by malicious home gateways. Rathore et al. [<xref ref-type="bibr" rid="B34">34</xref>] proposed a high-speed real-time scheme. The scheme is divided into four stages: registration, key exchange, key revocation, and data transmission. Although the scheme achieves real-time high-speed data transmission with careful consideration of details like timestamps, it employs a large number of signature algorithms and asymmetric encryption algorithms to ensure data integrity, data identity authentication, and secure key agreement. This results in high computational overhead for the entire smart city system. Hui et al. [<xref ref-type="bibr" rid="B35">35</xref>] proposed a novel data transmission scheme for Industrial IoT, based on a chaotic system and utilizing a linear n-shift encryption mechanism, which also includes a synchronization mechanism. However, this scheme lacks a reliable key update mechanism, making it vulnerable to ciphertext analysis attacks.</p>
</sec>
<sec id="s4">
<title>3 Preliminaries</title>
<sec id="s4-1">
<title>3.1 Model</title>
<p>This paper delves into the secure interaction mechanisms for electronic evidence, with the core objective of ensuring the privacy and security of electronic evidence during its transfer, thereby upholding the dual requirements of judicial fairness and data protection. As shown in <xref ref-type="fig" rid="F1">Figure 1</xref>, this electronic evidence interaction model is meticulously constructed and consists of three core components: the trust registration center (TRC), user, the storage center.</p>
<fig id="F1" position="float">
<label>FIGURE 1</label>
<caption>
<p>System model.</p>
</caption>
<graphic xlink:href="fphy-13-1522170-g001.tif"/>
</fig>
<p>As the cornerstone of the model, TRC acts as a trusted third party. Its primary responsibility is system initialization, including generating the necessary security parameters and related configurations, laying a solid foundation for subsequent secure interactions. Additionally, TRC is responsible for the registration management of users and storage centers, ensuring that only legitimate and trusted entities can join the system through rigorous identity verification processes. In the electronic evidence interaction model, the user base is extensive and diverse, encompassing key judicial and law enforcement agencies such as courts, public security departments, procuratorates, forensic identification centers, arbitration committees, and notary offices. These users not only perform core operations such as uploading, forwarding, downloading, and reviewing evidence within the model but also ensure the legality and validity of the electronic evidence transfer through their expertise and authority. Notably, when interacting with the storage center, users, with the assistance of the TRA, use the key agreement mechanism to jointly generate a shared session key with the storage center. This key is used to encrypt all subsequent communications, ensuring the confidentiality and integrity of data transmission.</p>
<p>As the centralized platform for storing and managing electronic evidence, the storage center plays a crucial role. It stores the received electronic evidence to prevent unauthorized access and tampering. The storage center also enforces strict access control policies, precisely regulating user access to electronic evidence based on their permissions and identity. Additionally, to mitigate the risks of potential data loss or damage, the storage center employs strategies such as multi-replica storage, regular backups, and disaster recovery, ensuring high availability and durability of electronic evidence data. When providing upload and download services to users, the storage center uses the session key previously negotiated with the user to encrypt and decrypt the transmitted data, thus achieving secure end-to-end interaction.</p>
<p>In our security model, we assume that the TRC is a trusted entity with sufficient computational power to resist various known security attacks. TRC communicates with other entities through wired or secure channels and does not exhibit malicious behavior towards users during the registration process. The storage center is assumed to be a semi-trusted entity, meaning it is curious about the user&#x2019;s privacy and is motivated to obtain it, but it will not conduct malicious attacks and will adhere to the protocol to execute the corresponding operations. The user is assumed to communicate with the storage center via an insecure wireless channel, which may be subject to various network security attacks from attackers. We consider the user to be an untrusted entity, meaning there may be malicious entities, such as compromised electric vehicles, that could carry out tampering, replay, delay, and other network security attacks on the system.</p>
</sec>
<sec id="s4-2">
<title>3.2 Chebyshev chaotic map</title>
<p>In this scheme, we employ an extended Chebyshev polynomial with enhanced security [<xref ref-type="bibr" rid="B36">36</xref>]. It is defined as follows:</p>
<p>
<statement content-type="definition" id="Definition_1">
<label>Definition 1</label>
<p>Let n be an integer and <inline-formula id="inf1">
<mml:math id="m1">
<mml:mrow>
<mml:mi>x</mml:mi>
<mml:mo>&#x2208;</mml:mo>
<mml:mrow>
<mml:mfenced open="[" close="]" separators="|">
<mml:mrow>
<mml:mo>&#x2212;</mml:mo>
<mml:mn>1</mml:mn>
<mml:mo>,</mml:mo>
<mml:mn>1</mml:mn>
</mml:mrow>
</mml:mfenced>
</mml:mrow>
</mml:mrow>
</mml:math>
</inline-formula>, chebyshev polynomial is defined as <xref ref-type="disp-formula" rid="e1">Equations 1</xref>, <xref ref-type="disp-formula" rid="e2">2</xref>
<disp-formula id="e1">
<mml:math id="m2">
<mml:mrow>
<mml:msub>
<mml:mi>T</mml:mi>
<mml:mi>n</mml:mi>
</mml:msub>
<mml:mrow>
<mml:mfenced open="(" close=")" separators="|">
<mml:mrow>
<mml:mi>x</mml:mi>
</mml:mrow>
</mml:mfenced>
</mml:mrow>
<mml:mo>&#x3d;</mml:mo>
<mml:mi mathvariant="italic">cos</mml:mi>
<mml:mrow>
<mml:mfenced open="(" close=")" separators="|">
<mml:mrow>
<mml:mi>n</mml:mi>
<mml:mo>&#x22c5;</mml:mo>
<mml:mi mathvariant="italic">arccos</mml:mi>
<mml:mrow>
<mml:mfenced open="(" close=")" separators="|">
<mml:mrow>
<mml:mi>x</mml:mi>
</mml:mrow>
</mml:mfenced>
</mml:mrow>
</mml:mrow>
</mml:mfenced>
</mml:mrow>
</mml:mrow>
</mml:math>
<label>(1)</label>
</disp-formula>
<disp-formula id="e2">
<mml:math id="m3">
<mml:mrow>
<mml:msub>
<mml:mi>T</mml:mi>
<mml:mi>n</mml:mi>
</mml:msub>
<mml:mrow>
<mml:mfenced open="(" close=")" separators="|">
<mml:mrow>
<mml:mi>x</mml:mi>
</mml:mrow>
</mml:mfenced>
</mml:mrow>
<mml:mo>&#x3d;</mml:mo>
<mml:mn>2</mml:mn>
<mml:mi>x</mml:mi>
<mml:msub>
<mml:mi>T</mml:mi>
<mml:mrow>
<mml:mi>n</mml:mi>
<mml:mo>&#x2212;</mml:mo>
<mml:mn>1</mml:mn>
</mml:mrow>
</mml:msub>
<mml:mrow>
<mml:mfenced open="(" close=")" separators="|">
<mml:mrow>
<mml:mi>x</mml:mi>
</mml:mrow>
</mml:mfenced>
</mml:mrow>
<mml:mo>&#x2212;</mml:mo>
<mml:msub>
<mml:mi>T</mml:mi>
<mml:mrow>
<mml:mi>n</mml:mi>
<mml:mo>&#x2212;</mml:mo>
<mml:mn>2</mml:mn>
</mml:mrow>
</mml:msub>
<mml:mrow>
<mml:mfenced open="(" close=")" separators="|">
<mml:mrow>
<mml:mi>x</mml:mi>
</mml:mrow>
</mml:mfenced>
</mml:mrow>
<mml:mrow>
<mml:mfenced open="(" close=")" separators="|">
<mml:mrow>
<mml:mi>m</mml:mi>
<mml:mi>o</mml:mi>
<mml:mi>d</mml:mi>
<mml:mi>p</mml:mi>
</mml:mrow>
</mml:mfenced>
</mml:mrow>
</mml:mrow>
</mml:math>
<label>(2)</label>
</disp-formula>
</p>
<p>Zhang [<xref ref-type="bibr" rid="B37">37</xref>] demonstrated that the semigroup property of chebyshev polynomials also holds.</p>
</statement>
</p>
<p>
<statement content-type="definition" id="Definition_2">
<label>Definition 2</label>
<p>(Chaotic Map-Based Diffie-Hellman Problem (CMBDHP)): Given x, <inline-formula id="inf2">
<mml:math id="m4">
<mml:mrow>
<mml:msub>
<mml:mi>T</mml:mi>
<mml:mi>s</mml:mi>
</mml:msub>
<mml:mrow>
<mml:mfenced open="(" close=")" separators="|">
<mml:mrow>
<mml:mi>x</mml:mi>
</mml:mrow>
</mml:mfenced>
</mml:mrow>
</mml:mrow>
</mml:math>
</inline-formula> and <inline-formula id="inf3">
<mml:math id="m5">
<mml:mrow>
<mml:msub>
<mml:mi>T</mml:mi>
<mml:mi>r</mml:mi>
</mml:msub>
<mml:mrow>
<mml:mfenced open="(" close=")" separators="|">
<mml:mrow>
<mml:mi>x</mml:mi>
</mml:mrow>
</mml:mfenced>
</mml:mrow>
</mml:mrow>
</mml:math>
</inline-formula>, it is almost impossible to find <inline-formula id="inf4">
<mml:math id="m6">
<mml:mrow>
<mml:msub>
<mml:mi>T</mml:mi>
<mml:mrow>
<mml:mi>r</mml:mi>
<mml:mi>s</mml:mi>
</mml:mrow>
</mml:msub>
<mml:mrow>
<mml:mfenced open="(" close=")" separators="|">
<mml:mrow>
<mml:mi>x</mml:mi>
</mml:mrow>
</mml:mfenced>
</mml:mrow>
</mml:mrow>
</mml:math>
</inline-formula>.</p>
</statement>
</p>
</sec>
</sec>
<sec id="s5">
<title>4 Proposed protocol</title>
<p>This paper proposes an interaction scheme for electronic evidence in IoT. <xref ref-type="fig" rid="F2">Figure 2</xref> shows the authentication flow.</p>
<fig id="F2" position="float">
<label>FIGURE 2</label>
<caption>
<p>Authentication flow.</p>
</caption>
<graphic xlink:href="fphy-13-1522170-g002.tif"/>
</fig>
<sec id="s5-1">
<title>4.1 System setup phase</title>
<p>At this stage, TRC generates its master private key and other public system parameters.<list list-type="simple">
<list-item>
<p>1. TRC selects a large prime number p and a hash function <inline-formula id="inf5">
<mml:math id="m7">
<mml:mrow>
<mml:mi>H</mml:mi>
<mml:mrow>
<mml:mfenced open="(" close=")" separators="|">
<mml:mrow>
<mml:mo>&#xb7;</mml:mo>
</mml:mrow>
</mml:mfenced>
</mml:mrow>
</mml:mrow>
</mml:math>
</inline-formula>. Simultaneously, TRC chooses s and x from <inline-formula id="inf6">
<mml:math id="m8">
<mml:mrow>
<mml:mfenced open="(" close=")" separators="|">
<mml:mrow>
<mml:mo>&#x2212;</mml:mo>
<mml:mi>&#x221e;</mml:mi>
<mml:mo>,</mml:mo>
<mml:mo>&#x2b;</mml:mo>
<mml:mi>&#x221e;</mml:mi>
</mml:mrow>
</mml:mfenced>
</mml:mrow>
</mml:math>
</inline-formula>, where s serves as its master private key, and computes the public key <inline-formula id="inf7">
<mml:math id="m9">
<mml:mrow>
<mml:msub>
<mml:mi>S</mml:mi>
<mml:mrow>
<mml:mi>p</mml:mi>
<mml:mi>u</mml:mi>
<mml:mi>b</mml:mi>
</mml:mrow>
</mml:msub>
<mml:mo>&#x3d;</mml:mo>
<mml:msub>
<mml:mi>T</mml:mi>
<mml:mi>s</mml:mi>
</mml:msub>
<mml:mrow>
<mml:mfenced open="(" close=")" separators="|">
<mml:mrow>
<mml:mi>x</mml:mi>
</mml:mrow>
</mml:mfenced>
</mml:mrow>
</mml:mrow>
</mml:math>
</inline-formula>.</p>
</list-item>
<list-item>
<p>2. TRC securely and confidentially stores the private key s, and publicly releases the system parameters <inline-formula id="inf8">
<mml:math id="m10">
<mml:mrow>
<mml:mi>P</mml:mi>
<mml:mo>&#x3d;</mml:mo>
<mml:mrow>
<mml:mfenced open="{" close="}" separators="|">
<mml:mrow>
<mml:mi>p</mml:mi>
<mml:mo>,</mml:mo>
<mml:mi>x</mml:mi>
<mml:mo>,</mml:mo>
<mml:msub>
<mml:mi>S</mml:mi>
<mml:mrow>
<mml:mi>p</mml:mi>
<mml:mi>u</mml:mi>
<mml:mi>b</mml:mi>
</mml:mrow>
</mml:msub>
</mml:mrow>
</mml:mfenced>
</mml:mrow>
</mml:mrow>
</mml:math>
</inline-formula>.</p>
</list-item>
</list>
</p>
</sec>
<sec id="s5-2">
<title>4.2 User registration</title>
<p>
<list list-type="simple">
<list-item>
<p>1. <inline-formula id="inf9">
<mml:math id="m11">
<mml:mrow>
<mml:msub>
<mml:mi>U</mml:mi>
<mml:mi>i</mml:mi>
</mml:msub>
</mml:mrow>
</mml:math>
</inline-formula> first selects their identity identifier <inline-formula id="inf10">
<mml:math id="m12">
<mml:mrow>
<mml:mi>I</mml:mi>
<mml:msub>
<mml:mi>D</mml:mi>
<mml:mi>i</mml:mi>
</mml:msub>
</mml:mrow>
</mml:math>
</inline-formula> and password <inline-formula id="inf11">
<mml:math id="m13">
<mml:mrow>
<mml:mi>P</mml:mi>
<mml:msub>
<mml:mi>W</mml:mi>
<mml:mi>i</mml:mi>
</mml:msub>
</mml:mrow>
</mml:math>
</inline-formula>. Then it randomly selects a number <inline-formula id="inf12">
<mml:math id="m14">
<mml:mrow>
<mml:msub>
<mml:mi>w</mml:mi>
<mml:mi>i</mml:mi>
</mml:msub>
</mml:mrow>
</mml:math>
</inline-formula>, computes <inline-formula id="inf13">
<mml:math id="m15">
<mml:mrow>
<mml:mi>I</mml:mi>
<mml:msub>
<mml:mrow>
<mml:mi>D</mml:mi>
<mml:mi>W</mml:mi>
</mml:mrow>
<mml:mi>i</mml:mi>
</mml:msub>
<mml:mo>&#x3d;</mml:mo>
<mml:mi>H</mml:mi>
<mml:mrow>
<mml:mfenced open="(" close=")" separators="|">
<mml:mrow>
<mml:mi>I</mml:mi>
<mml:msub>
<mml:mi>D</mml:mi>
<mml:mi>i</mml:mi>
</mml:msub>
<mml:mo>,</mml:mo>
<mml:mi>P</mml:mi>
<mml:msub>
<mml:mi>W</mml:mi>
<mml:mi>i</mml:mi>
</mml:msub>
<mml:mo>,</mml:mo>
<mml:msub>
<mml:mi>w</mml:mi>
<mml:mi>i</mml:mi>
</mml:msub>
</mml:mrow>
</mml:mfenced>
</mml:mrow>
</mml:mrow>
</mml:math>
</inline-formula> and sends <inline-formula id="inf14">
<mml:math id="m16">
<mml:mrow>
<mml:mfenced open="{" close="}" separators="|">
<mml:mrow>
<mml:mi>I</mml:mi>
<mml:msub>
<mml:mi>D</mml:mi>
<mml:mi>i</mml:mi>
</mml:msub>
<mml:mo>,</mml:mo>
<mml:mi>I</mml:mi>
<mml:msub>
<mml:mrow>
<mml:mi>D</mml:mi>
<mml:mi>W</mml:mi>
</mml:mrow>
<mml:mi>i</mml:mi>
</mml:msub>
</mml:mrow>
</mml:mfenced>
</mml:mrow>
</mml:math>
</inline-formula> to the TRC.</p>
</list-item>
<list-item>
<p>2. Upon receiving <inline-formula id="inf15">
<mml:math id="m17">
<mml:mrow>
<mml:mfenced open="{" close="}" separators="|">
<mml:mrow>
<mml:mi>I</mml:mi>
<mml:msub>
<mml:mi>D</mml:mi>
<mml:mi>i</mml:mi>
</mml:msub>
<mml:mo>,</mml:mo>
<mml:mi>I</mml:mi>
<mml:msub>
<mml:mrow>
<mml:mi>D</mml:mi>
<mml:mi>W</mml:mi>
</mml:mrow>
<mml:mi>i</mml:mi>
</mml:msub>
</mml:mrow>
</mml:mfenced>
</mml:mrow>
</mml:math>
</inline-formula>, TRC calculates <inline-formula id="inf16">
<mml:math id="m18">
<mml:mrow>
<mml:mi>P</mml:mi>
<mml:mi>I</mml:mi>
<mml:msub>
<mml:mi>D</mml:mi>
<mml:mi>i</mml:mi>
</mml:msub>
<mml:mo>&#x3d;</mml:mo>
<mml:mi>H</mml:mi>
<mml:mrow>
<mml:mfenced open="(" close=")" separators="|">
<mml:mrow>
<mml:mi>I</mml:mi>
<mml:msub>
<mml:mi>D</mml:mi>
<mml:mi>i</mml:mi>
</mml:msub>
<mml:mo>,</mml:mo>
<mml:mi mathvariant="normal">s</mml:mi>
</mml:mrow>
</mml:mfenced>
</mml:mrow>
</mml:mrow>
</mml:math>
</inline-formula> and <inline-formula id="inf17">
<mml:math id="m19">
<mml:mrow>
<mml:msub>
<mml:mi>A</mml:mi>
<mml:mi>i</mml:mi>
</mml:msub>
<mml:mo>&#x3d;</mml:mo>
<mml:mi>H</mml:mi>
<mml:mrow>
<mml:mfenced open="(" close=")" separators="|">
<mml:mrow>
<mml:mi>I</mml:mi>
<mml:msub>
<mml:mi>D</mml:mi>
<mml:mi>i</mml:mi>
</mml:msub>
<mml:mo>,</mml:mo>
<mml:mi>I</mml:mi>
<mml:msub>
<mml:mrow>
<mml:mi>D</mml:mi>
<mml:mi>W</mml:mi>
</mml:mrow>
<mml:mi>i</mml:mi>
</mml:msub>
<mml:mo>,</mml:mo>
<mml:mi>s</mml:mi>
</mml:mrow>
</mml:mfenced>
</mml:mrow>
</mml:mrow>
</mml:math>
</inline-formula>, and securely stores <inline-formula id="inf18">
<mml:math id="m20">
<mml:mrow>
<mml:mfenced open="(" close=")" separators="|">
<mml:mrow>
<mml:mi>I</mml:mi>
<mml:msub>
<mml:mi>D</mml:mi>
<mml:mi>i</mml:mi>
</mml:msub>
<mml:mo>,</mml:mo>
<mml:msub>
<mml:mi>A</mml:mi>
<mml:mi>i</mml:mi>
</mml:msub>
<mml:mo>,</mml:mo>
<mml:mi>P</mml:mi>
<mml:mi>I</mml:mi>
<mml:msub>
<mml:mi>D</mml:mi>
<mml:mi>i</mml:mi>
</mml:msub>
</mml:mrow>
</mml:mfenced>
</mml:mrow>
</mml:math>
</inline-formula> in its database. TRC then securely sends <inline-formula id="inf19">
<mml:math id="m21">
<mml:mrow>
<mml:mfenced open="{" close="}" separators="|">
<mml:mrow>
<mml:mi>P</mml:mi>
<mml:mi>I</mml:mi>
<mml:msub>
<mml:mi>D</mml:mi>
<mml:mi>i</mml:mi>
</mml:msub>
<mml:mo>,</mml:mo>
<mml:msub>
<mml:mi>A</mml:mi>
<mml:mi>i</mml:mi>
</mml:msub>
</mml:mrow>
</mml:mfenced>
</mml:mrow>
</mml:math>
</inline-formula> to <inline-formula id="inf20">
<mml:math id="m22">
<mml:mrow>
<mml:msub>
<mml:mi>U</mml:mi>
<mml:mi>i</mml:mi>
</mml:msub>
</mml:mrow>
</mml:math>
</inline-formula>. Otherwise, TRC rejects the request.</p>
</list-item>
<list-item>
<p>3. Upon receiving the response message <inline-formula id="inf21">
<mml:math id="m23">
<mml:mrow>
<mml:mfenced open="{" close="}" separators="|">
<mml:mrow>
<mml:mi>P</mml:mi>
<mml:mi>I</mml:mi>
<mml:msub>
<mml:mi>D</mml:mi>
<mml:mi>i</mml:mi>
</mml:msub>
<mml:mo>,</mml:mo>
<mml:msub>
<mml:mi>A</mml:mi>
<mml:mi>i</mml:mi>
</mml:msub>
</mml:mrow>
</mml:mfenced>
</mml:mrow>
</mml:math>
</inline-formula>, <inline-formula id="inf22">
<mml:math id="m24">
<mml:msub>
<mml:mi>U</mml:mi>
<mml:mi>i</mml:mi>
</mml:msub>
</mml:math>
</inline-formula> computes <inline-formula id="inf23">
<mml:math id="m25">
<mml:mrow>
<mml:msub>
<mml:mi>A</mml:mi>
<mml:mi>i</mml:mi>
</mml:msub>
<mml:mo>&#x2a;</mml:mo>
<mml:mo>&#x3d;</mml:mo>
<mml:mi mathvariant="normal">H</mml:mi>
<mml:mrow>
<mml:mfenced open="(" close=")" separators="|">
<mml:mrow>
<mml:mi>I</mml:mi>
<mml:msub>
<mml:mi>D</mml:mi>
<mml:mi>i</mml:mi>
</mml:msub>
<mml:mo>,</mml:mo>
<mml:mi>P</mml:mi>
<mml:msub>
<mml:mi>W</mml:mi>
<mml:mi>i</mml:mi>
</mml:msub>
</mml:mrow>
</mml:mfenced>
</mml:mrow>
<mml:mo>&#x2295;</mml:mo>
<mml:msub>
<mml:mi>A</mml:mi>
<mml:mi>i</mml:mi>
</mml:msub>
</mml:mrow>
</mml:math>
</inline-formula> and <inline-formula id="inf24">
<mml:math id="m26">
<mml:mrow>
<mml:mi>P</mml:mi>
<mml:mi>I</mml:mi>
<mml:msubsup>
<mml:mi>D</mml:mi>
<mml:mi>i</mml:mi>
<mml:mo>&#x2a;</mml:mo>
</mml:msubsup>
<mml:mo>&#x3d;</mml:mo>
<mml:mi>h</mml:mi>
<mml:mrow>
<mml:mfenced open="(" close=")" separators="|">
<mml:mrow>
<mml:mi>I</mml:mi>
<mml:msub>
<mml:mi>D</mml:mi>
<mml:mi>i</mml:mi>
</mml:msub>
<mml:mo>,</mml:mo>
<mml:mi>P</mml:mi>
<mml:msub>
<mml:mi>W</mml:mi>
<mml:mi>i</mml:mi>
</mml:msub>
<mml:mo>,</mml:mo>
<mml:msub>
<mml:mi>A</mml:mi>
<mml:mi>i</mml:mi>
</mml:msub>
</mml:mrow>
</mml:mfenced>
</mml:mrow>
<mml:mo>&#x2295;</mml:mo>
<mml:mi>P</mml:mi>
<mml:mi>I</mml:mi>
<mml:msub>
<mml:mi>D</mml:mi>
<mml:mi>i</mml:mi>
</mml:msub>
</mml:mrow>
</mml:math>
</inline-formula>. Finally, <inline-formula id="inf25">
<mml:math id="m27">
<mml:mrow>
<mml:msub>
<mml:mi>U</mml:mi>
<mml:mi>i</mml:mi>
</mml:msub>
</mml:mrow>
</mml:math>
</inline-formula> securely stores <inline-formula id="inf26">
<mml:math id="m28">
<mml:mrow>
<mml:mfenced open="(" close=")" separators="|">
<mml:mrow>
<mml:msub>
<mml:mi>A</mml:mi>
<mml:mi>i</mml:mi>
</mml:msub>
<mml:mo>&#x2a;</mml:mo>
<mml:mo>,</mml:mo>
<mml:mi>P</mml:mi>
<mml:mi>I</mml:mi>
<mml:msubsup>
<mml:mi>D</mml:mi>
<mml:mi>i</mml:mi>
<mml:mo>&#x2a;</mml:mo>
</mml:msubsup>
</mml:mrow>
</mml:mfenced>
</mml:mrow>
</mml:math>
</inline-formula>.</p>
</list-item>
</list>
</p>
</sec>
<sec id="s5-3">
<title>4.3 Storage center registration</title>
<p>
<list list-type="simple">
<list-item>
<p>1. <inline-formula id="inf27">
<mml:math id="m29">
<mml:mrow>
<mml:msub>
<mml:mrow>
<mml:mi>S</mml:mi>
<mml:mi>C</mml:mi>
</mml:mrow>
<mml:mi>j</mml:mi>
</mml:msub>
</mml:mrow>
</mml:math>
</inline-formula> selects its identity identifier <inline-formula id="inf28">
<mml:math id="m30">
<mml:mrow>
<mml:mi>I</mml:mi>
<mml:msub>
<mml:mi>D</mml:mi>
<mml:mi>j</mml:mi>
</mml:msub>
</mml:mrow>
</mml:math>
</inline-formula> and sends it to TRC.</p>
</list-item>
<list-item>
<p>2. Upon receiving <inline-formula id="inf29">
<mml:math id="m31">
<mml:mrow>
<mml:msub>
<mml:mrow>
<mml:mi>S</mml:mi>
<mml:mi>C</mml:mi>
</mml:mrow>
<mml:mi>j</mml:mi>
</mml:msub>
</mml:mrow>
</mml:math>
</inline-formula>&#x27;s request, TRC randomly selects a number <inline-formula id="inf30">
<mml:math id="m32">
<mml:mrow>
<mml:msub>
<mml:mi>n</mml:mi>
<mml:mi>j</mml:mi>
</mml:msub>
</mml:mrow>
</mml:math>
</inline-formula>, calculates <inline-formula id="inf31">
<mml:math id="m33">
<mml:mrow>
<mml:mi>S</mml:mi>
<mml:mi>I</mml:mi>
<mml:msub>
<mml:mi>D</mml:mi>
<mml:mi>j</mml:mi>
</mml:msub>
<mml:mo>&#x3d;</mml:mo>
<mml:mi>H</mml:mi>
<mml:mrow>
<mml:mfenced open="(" close=")" separators="|">
<mml:mrow>
<mml:mi>I</mml:mi>
<mml:msub>
<mml:mi>D</mml:mi>
<mml:mi>j</mml:mi>
</mml:msub>
<mml:mo>,</mml:mo>
<mml:msub>
<mml:mi>n</mml:mi>
<mml:mi>j</mml:mi>
</mml:msub>
</mml:mrow>
</mml:mfenced>
</mml:mrow>
</mml:mrow>
</mml:math>
</inline-formula> and <inline-formula id="inf32">
<mml:math id="m34">
<mml:mrow>
<mml:msub>
<mml:mi>B</mml:mi>
<mml:mi>j</mml:mi>
</mml:msub>
<mml:mo>&#x3d;</mml:mo>
<mml:mi>H</mml:mi>
<mml:mrow>
<mml:mfenced open="(" close=")" separators="|">
<mml:mrow>
<mml:mi>I</mml:mi>
<mml:msub>
<mml:mi>D</mml:mi>
<mml:mi>j</mml:mi>
</mml:msub>
<mml:mo>,</mml:mo>
<mml:mi>s</mml:mi>
</mml:mrow>
</mml:mfenced>
</mml:mrow>
</mml:mrow>
</mml:math>
</inline-formula>, and securely stores <inline-formula id="inf33">
<mml:math id="m35">
<mml:mrow>
<mml:mfenced open="(" close=")" separators="|">
<mml:mrow>
<mml:mi>I</mml:mi>
<mml:msub>
<mml:mi>D</mml:mi>
<mml:mi>j</mml:mi>
</mml:msub>
<mml:mo>,</mml:mo>
<mml:mi>S</mml:mi>
<mml:mi>I</mml:mi>
<mml:msub>
<mml:mi>D</mml:mi>
<mml:mi>j</mml:mi>
</mml:msub>
</mml:mrow>
</mml:mfenced>
</mml:mrow>
</mml:math>
</inline-formula>. Finally, TRC sends <inline-formula id="inf34">
<mml:math id="m36">
<mml:mrow>
<mml:mfenced open="{" close="}" separators="|">
<mml:mrow>
<mml:mi>S</mml:mi>
<mml:mi>I</mml:mi>
<mml:msub>
<mml:mi>D</mml:mi>
<mml:mi>j</mml:mi>
</mml:msub>
<mml:mo>,</mml:mo>
<mml:msub>
<mml:mi>B</mml:mi>
<mml:mi>j</mml:mi>
</mml:msub>
</mml:mrow>
</mml:mfenced>
</mml:mrow>
</mml:math>
</inline-formula> to <inline-formula id="inf35">
<mml:math id="m37">
<mml:mrow>
<mml:msub>
<mml:mrow>
<mml:mi>S</mml:mi>
<mml:mi>C</mml:mi>
</mml:mrow>
<mml:mi>j</mml:mi>
</mml:msub>
</mml:mrow>
</mml:math>
</inline-formula> via a secure channel.</p>
</list-item>
<list-item>
<p>3. Upon receiving the response message <inline-formula id="inf36">
<mml:math id="m38">
<mml:mrow>
<mml:mfenced open="{" close="}" separators="|">
<mml:mrow>
<mml:mi>S</mml:mi>
<mml:mi>I</mml:mi>
<mml:msub>
<mml:mi>D</mml:mi>
<mml:mi>j</mml:mi>
</mml:msub>
<mml:mo>,</mml:mo>
<mml:msub>
<mml:mi>B</mml:mi>
<mml:mi>j</mml:mi>
</mml:msub>
</mml:mrow>
</mml:mfenced>
</mml:mrow>
</mml:math>
</inline-formula>, <inline-formula id="inf37">
<mml:math id="m39">
<mml:mrow>
<mml:msub>
<mml:mrow>
<mml:mi>S</mml:mi>
<mml:mi>C</mml:mi>
</mml:mrow>
<mml:mi>j</mml:mi>
</mml:msub>
</mml:mrow>
</mml:math>
</inline-formula> stores <inline-formula id="inf38">
<mml:math id="m40">
<mml:mrow>
<mml:mfenced open="{" close="}" separators="|">
<mml:mrow>
<mml:mi>S</mml:mi>
<mml:mi>I</mml:mi>
<mml:msub>
<mml:mi>D</mml:mi>
<mml:mi>j</mml:mi>
</mml:msub>
<mml:mo>,</mml:mo>
<mml:msub>
<mml:mi>B</mml:mi>
<mml:mi>j</mml:mi>
</mml:msub>
</mml:mrow>
</mml:mfenced>
</mml:mrow>
</mml:math>
</inline-formula> in a secure storage area and publicly discloses <inline-formula id="inf39">
<mml:math id="m41">
<mml:mrow>
<mml:mi>S</mml:mi>
<mml:mi>I</mml:mi>
<mml:msub>
<mml:mi>D</mml:mi>
<mml:mi>j</mml:mi>
</mml:msub>
</mml:mrow>
</mml:math>
</inline-formula>.</p>
</list-item>
</list>
</p>
</sec>
<sec id="s5-4">
<title>4.4 Authentication key agreement phase</title>
<list list-type="simple">
<list-item>
<p>1. As shown in <xref ref-type="fig" rid="F3">Figure 3</xref>, <inline-formula id="inf40">
<mml:math id="m42">
<mml:mrow>
<mml:msub>
<mml:mi>U</mml:mi>
<mml:mi>i</mml:mi>
</mml:msub>
</mml:mrow>
</mml:math>
</inline-formula> first inputs their identity identifier <inline-formula id="inf41">
<mml:math id="m43">
<mml:mrow>
<mml:mi>I</mml:mi>
<mml:msub>
<mml:mi>D</mml:mi>
<mml:mi>i</mml:mi>
</mml:msub>
</mml:mrow>
</mml:math>
</inline-formula> and password <inline-formula id="inf42">
<mml:math id="m44">
<mml:mrow>
<mml:mi>P</mml:mi>
<mml:msub>
<mml:mi>W</mml:mi>
<mml:mi>i</mml:mi>
</mml:msub>
</mml:mrow>
</mml:math>
</inline-formula> into their mobile device. Then it computes <inline-formula id="inf43">
<mml:math id="m45">
<mml:mrow>
<mml:msub>
<mml:mi>A</mml:mi>
<mml:mi>i</mml:mi>
</mml:msub>
<mml:mo>&#x3d;</mml:mo>
<mml:mi mathvariant="normal">H</mml:mi>
<mml:mrow>
<mml:mfenced open="(" close=")" separators="|">
<mml:mrow>
<mml:mi>I</mml:mi>
<mml:msub>
<mml:mi>D</mml:mi>
<mml:mi>i</mml:mi>
</mml:msub>
<mml:mo>,</mml:mo>
<mml:mi>P</mml:mi>
<mml:msub>
<mml:mi>W</mml:mi>
<mml:mi>i</mml:mi>
</mml:msub>
</mml:mrow>
</mml:mfenced>
</mml:mrow>
<mml:mo>&#x2295;</mml:mo>
<mml:msub>
<mml:mi>A</mml:mi>
<mml:mi>i</mml:mi>
</mml:msub>
<mml:mo>&#x2a;</mml:mo>
</mml:mrow>
</mml:math>
</inline-formula> and the pseudonym <inline-formula id="inf44">
<mml:math id="m46">
<mml:mrow>
<mml:mi>P</mml:mi>
<mml:mi>I</mml:mi>
<mml:msub>
<mml:mi>D</mml:mi>
<mml:mi>i</mml:mi>
</mml:msub>
<mml:mo>&#x3d;</mml:mo>
<mml:mi>H</mml:mi>
<mml:mrow>
<mml:mfenced open="(" close=")" separators="|">
<mml:mrow>
<mml:mi>I</mml:mi>
<mml:msub>
<mml:mi>D</mml:mi>
<mml:mi>i</mml:mi>
</mml:msub>
<mml:mo>,</mml:mo>
<mml:mi>P</mml:mi>
<mml:msub>
<mml:mi>W</mml:mi>
<mml:mi>i</mml:mi>
</mml:msub>
<mml:mo>,</mml:mo>
<mml:msub>
<mml:mi>A</mml:mi>
<mml:mi>i</mml:mi>
</mml:msub>
</mml:mrow>
</mml:mfenced>
</mml:mrow>
<mml:mo>&#x2295;</mml:mo>
<mml:mi>P</mml:mi>
<mml:mi>I</mml:mi>
<mml:msubsup>
<mml:mi>D</mml:mi>
<mml:mi>i</mml:mi>
<mml:mo>&#x2a;</mml:mo>
</mml:msubsup>
</mml:mrow>
</mml:math>
</inline-formula>. <inline-formula id="inf45">
<mml:math id="m47">
<mml:mrow>
<mml:msub>
<mml:mi>U</mml:mi>
<mml:mi>i</mml:mi>
</mml:msub>
</mml:mrow>
</mml:math>
</inline-formula> then randomly selects two numbers <inline-formula id="inf46">
<mml:math id="m48">
<mml:mrow>
<mml:msub>
<mml:mi>c</mml:mi>
<mml:mi>i</mml:mi>
</mml:msub>
<mml:mo>,</mml:mo>
<mml:msub>
<mml:mi>y</mml:mi>
<mml:mi>i</mml:mi>
</mml:msub>
</mml:mrow>
</mml:math>
</inline-formula> and current timestamp <inline-formula id="inf47">
<mml:math id="m49">
<mml:mrow>
<mml:msub>
<mml:mi>T</mml:mi>
<mml:mn>1</mml:mn>
</mml:msub>
</mml:mrow>
</mml:math>
</inline-formula>, computes the following message, and sends an authentication request message <inline-formula id="inf48">
<mml:math id="m50">
<mml:mrow>
<mml:mfenced open="{" close="}" separators="|">
<mml:mrow>
<mml:msub>
<mml:mi>V</mml:mi>
<mml:mn>1</mml:mn>
</mml:msub>
<mml:mo>,</mml:mo>
<mml:msub>
<mml:mi>V</mml:mi>
<mml:mn>3</mml:mn>
</mml:msub>
<mml:mo>,</mml:mo>
<mml:msub>
<mml:mi>V</mml:mi>
<mml:mn>4</mml:mn>
</mml:msub>
<mml:mo>,</mml:mo>
<mml:msub>
<mml:mi>V</mml:mi>
<mml:mn>5</mml:mn>
</mml:msub>
<mml:mo>,</mml:mo>
<mml:msub>
<mml:mi>V</mml:mi>
<mml:mn>6</mml:mn>
</mml:msub>
<mml:mo>,</mml:mo>
<mml:msub>
<mml:mi>T</mml:mi>
<mml:mn>1</mml:mn>
</mml:msub>
</mml:mrow>
</mml:mfenced>
</mml:mrow>
</mml:math>
</inline-formula> to TRC via a public channel.</p>
</list-item>
</list>
<disp-formula id="equ1">
<mml:math id="m51">
<mml:mrow>
<mml:msub>
<mml:mi>V</mml:mi>
<mml:mn>1</mml:mn>
</mml:msub>
<mml:mo>&#x3d;</mml:mo>
<mml:msub>
<mml:mi>T</mml:mi>
<mml:msub>
<mml:mi>c</mml:mi>
<mml:mi>i</mml:mi>
</mml:msub>
</mml:msub>
<mml:mrow>
<mml:mfenced open="(" close=")" separators="|">
<mml:mrow>
<mml:mi>x</mml:mi>
</mml:mrow>
</mml:mfenced>
</mml:mrow>
<mml:mtext>&#x2009;</mml:mtext>
<mml:mi mathvariant="italic">mod</mml:mi>
<mml:mtext>&#x2009;</mml:mtext>
<mml:mi>p</mml:mi>
</mml:mrow>
</mml:math>
</disp-formula>
<disp-formula id="equ2">
<mml:math id="m52">
<mml:mrow>
<mml:msub>
<mml:mi>V</mml:mi>
<mml:mn>2</mml:mn>
</mml:msub>
<mml:mo>&#x3d;</mml:mo>
<mml:msub>
<mml:mi>T</mml:mi>
<mml:msub>
<mml:mi>c</mml:mi>
<mml:mi>i</mml:mi>
</mml:msub>
</mml:msub>
<mml:mrow>
<mml:mfenced open="(" close=")" separators="|">
<mml:mrow>
<mml:mtext>&#x2009;</mml:mtext>
<mml:msub>
<mml:mi>S</mml:mi>
<mml:mrow>
<mml:mi>p</mml:mi>
<mml:mi>u</mml:mi>
<mml:mi>b</mml:mi>
</mml:mrow>
</mml:msub>
</mml:mrow>
</mml:mfenced>
</mml:mrow>
<mml:mtext>&#x2009;</mml:mtext>
<mml:mi mathvariant="italic">mod</mml:mi>
<mml:mtext>&#x2009;</mml:mtext>
<mml:mi>p</mml:mi>
</mml:mrow>
</mml:math>
</disp-formula>
<disp-formula id="equ3">
<mml:math id="m53">
<mml:mrow>
<mml:msub>
<mml:mi>V</mml:mi>
<mml:mn>3</mml:mn>
</mml:msub>
<mml:mo>&#x3d;</mml:mo>
<mml:mi>H</mml:mi>
<mml:mrow>
<mml:mfenced open="(" close=")" separators="|">
<mml:mrow>
<mml:msub>
<mml:mi>V</mml:mi>
<mml:mn>2</mml:mn>
</mml:msub>
<mml:mo>,</mml:mo>
<mml:msub>
<mml:mi>T</mml:mi>
<mml:mn>1</mml:mn>
</mml:msub>
</mml:mrow>
</mml:mfenced>
</mml:mrow>
<mml:mo>&#x2295;</mml:mo>
<mml:mi>P</mml:mi>
<mml:mi>I</mml:mi>
<mml:msub>
<mml:mi>D</mml:mi>
<mml:mi>i</mml:mi>
</mml:msub>
</mml:mrow>
</mml:math>
</disp-formula>
<disp-formula id="equ4">
<mml:math id="m54">
<mml:mrow>
<mml:msub>
<mml:mi>V</mml:mi>
<mml:mn>4</mml:mn>
</mml:msub>
<mml:mo>&#x3d;</mml:mo>
<mml:mi>H</mml:mi>
<mml:mrow>
<mml:mfenced open="(" close=")" separators="|">
<mml:mrow>
<mml:mi>P</mml:mi>
<mml:mi>I</mml:mi>
<mml:msub>
<mml:mi>D</mml:mi>
<mml:mi>i</mml:mi>
</mml:msub>
<mml:mo>,</mml:mo>
<mml:msub>
<mml:mi>V</mml:mi>
<mml:mn>2</mml:mn>
</mml:msub>
<mml:mo>,</mml:mo>
<mml:msub>
<mml:mi>T</mml:mi>
<mml:mn>1</mml:mn>
</mml:msub>
</mml:mrow>
</mml:mfenced>
</mml:mrow>
<mml:mo>&#x2295;</mml:mo>
<mml:msub>
<mml:mi>y</mml:mi>
<mml:mi>i</mml:mi>
</mml:msub>
</mml:mrow>
</mml:math>
</disp-formula>
<disp-formula id="equ5">
<mml:math id="m55">
<mml:mrow>
<mml:msub>
<mml:mi>V</mml:mi>
<mml:mn>5</mml:mn>
</mml:msub>
<mml:mo>&#x3d;</mml:mo>
<mml:mi>H</mml:mi>
<mml:mrow>
<mml:mfenced open="(" close=")" separators="|">
<mml:mrow>
<mml:mi>P</mml:mi>
<mml:mi>I</mml:mi>
<mml:msub>
<mml:mi>D</mml:mi>
<mml:mi>i</mml:mi>
</mml:msub>
<mml:mo>,</mml:mo>
<mml:msub>
<mml:mi>V</mml:mi>
<mml:mn>2</mml:mn>
</mml:msub>
<mml:mo>,</mml:mo>
<mml:msub>
<mml:mi>y</mml:mi>
<mml:mi>i</mml:mi>
</mml:msub>
<mml:mo>,</mml:mo>
<mml:msub>
<mml:mi>T</mml:mi>
<mml:mn>1</mml:mn>
</mml:msub>
</mml:mrow>
</mml:mfenced>
</mml:mrow>
<mml:mo>&#x2295;</mml:mo>
<mml:mi>S</mml:mi>
<mml:mi>I</mml:mi>
<mml:msub>
<mml:mi>D</mml:mi>
<mml:mi>j</mml:mi>
</mml:msub>
</mml:mrow>
</mml:math>
</disp-formula>
<disp-formula id="equ6">
<mml:math id="m56">
<mml:mrow>
<mml:msub>
<mml:mi>V</mml:mi>
<mml:mn>6</mml:mn>
</mml:msub>
<mml:mo>&#x3d;</mml:mo>
<mml:mi>H</mml:mi>
<mml:mrow>
<mml:mfenced open="(" close=")" separators="|">
<mml:mrow>
<mml:mi>S</mml:mi>
<mml:mi>I</mml:mi>
<mml:msub>
<mml:mi>D</mml:mi>
<mml:mi>j</mml:mi>
</mml:msub>
<mml:mo>,</mml:mo>
<mml:mi>I</mml:mi>
<mml:msub>
<mml:mi>D</mml:mi>
<mml:mi>i</mml:mi>
</mml:msub>
<mml:mo>,</mml:mo>
<mml:msub>
<mml:mi>V</mml:mi>
<mml:mn>2</mml:mn>
</mml:msub>
<mml:mo>,</mml:mo>
<mml:msub>
<mml:mi>y</mml:mi>
<mml:mi>i</mml:mi>
</mml:msub>
<mml:mo>,</mml:mo>
<mml:msub>
<mml:mi>A</mml:mi>
<mml:mi>i</mml:mi>
</mml:msub>
<mml:mo>,</mml:mo>
<mml:msub>
<mml:mi>T</mml:mi>
<mml:mn>1</mml:mn>
</mml:msub>
</mml:mrow>
</mml:mfenced>
</mml:mrow>
</mml:mrow>
</mml:math>
</disp-formula>
<list list-type="simple">
<list-item>
<p>2. Upon receiving the authentication request message <inline-formula id="inf49">
<mml:math id="m57">
<mml:mrow>
<mml:mfenced open="{" close="}" separators="|">
<mml:mrow>
<mml:msub>
<mml:mi>V</mml:mi>
<mml:mn>1</mml:mn>
</mml:msub>
<mml:mo>,</mml:mo>
<mml:msub>
<mml:mi>V</mml:mi>
<mml:mn>3</mml:mn>
</mml:msub>
<mml:mo>,</mml:mo>
<mml:msub>
<mml:mi>V</mml:mi>
<mml:mn>4</mml:mn>
</mml:msub>
<mml:mo>,</mml:mo>
<mml:msub>
<mml:mi>V</mml:mi>
<mml:mn>5</mml:mn>
</mml:msub>
<mml:mo>,</mml:mo>
<mml:msub>
<mml:mi>V</mml:mi>
<mml:mn>6</mml:mn>
</mml:msub>
<mml:mo>,</mml:mo>
<mml:msub>
<mml:mi>T</mml:mi>
<mml:mn>1</mml:mn>
</mml:msub>
</mml:mrow>
</mml:mfenced>
</mml:mrow>
</mml:math>
</inline-formula> from <inline-formula id="inf50">
<mml:math id="m58">
<mml:mrow>
<mml:msub>
<mml:mi>U</mml:mi>
<mml:mi>i</mml:mi>
</mml:msub>
</mml:mrow>
</mml:math>
</inline-formula>, TRC first verifies the validity of the timestamp <inline-formula id="inf51">
<mml:math id="m59">
<mml:mrow>
<mml:msub>
<mml:mi>T</mml:mi>
<mml:mn>1</mml:mn>
</mml:msub>
</mml:mrow>
</mml:math>
</inline-formula>. If the received authentication request message is valid, TRC proceeds to the next step; otherwise, TRC rejects the authentication request. TRC calculates <inline-formula id="inf52">
<mml:math id="m60">
<mml:mrow>
<mml:msubsup>
<mml:mi mathvariant="normal">V</mml:mi>
<mml:mn>2</mml:mn>
<mml:mo>&#x2a;</mml:mo>
</mml:msubsup>
<mml:mo>&#x3d;</mml:mo>
<mml:msub>
<mml:mi mathvariant="normal">T</mml:mi>
<mml:mi mathvariant="normal">s</mml:mi>
</mml:msub>
<mml:mrow>
<mml:mfenced open="(" close=")" separators="|">
<mml:mrow>
<mml:msub>
<mml:mi>V</mml:mi>
<mml:mn>1</mml:mn>
</mml:msub>
</mml:mrow>
</mml:mfenced>
</mml:mrow>
<mml:mtext>&#x2009;</mml:mtext>
<mml:mi mathvariant="italic">mod</mml:mi>
<mml:mtext>&#x2009;</mml:mtext>
<mml:mi>p</mml:mi>
</mml:mrow>
</mml:math>
</inline-formula> and <inline-formula id="inf53">
<mml:math id="m61">
<mml:mrow>
<mml:msubsup>
<mml:mrow>
<mml:mi>P</mml:mi>
<mml:mi>I</mml:mi>
<mml:mi>D</mml:mi>
</mml:mrow>
<mml:mi>i</mml:mi>
<mml:mo>&#x2a;</mml:mo>
</mml:msubsup>
<mml:mo>&#x3d;</mml:mo>
<mml:mi>H</mml:mi>
<mml:mrow>
<mml:mfenced open="(" close=")" separators="|">
<mml:mrow>
<mml:msub>
<mml:mi>V</mml:mi>
<mml:mn>2</mml:mn>
</mml:msub>
<mml:mo>,</mml:mo>
<mml:msub>
<mml:mi>T</mml:mi>
<mml:mn>1</mml:mn>
</mml:msub>
</mml:mrow>
</mml:mfenced>
</mml:mrow>
<mml:mo>&#x2295;</mml:mo>
<mml:msub>
<mml:mi>V</mml:mi>
<mml:mn>3</mml:mn>
</mml:msub>
</mml:mrow>
</mml:math>
</inline-formula>. Then, using the pseudonym <inline-formula id="inf54">
<mml:math id="m62">
<mml:mrow>
<mml:msubsup>
<mml:mrow>
<mml:mi>P</mml:mi>
<mml:mi>I</mml:mi>
<mml:mi>D</mml:mi>
</mml:mrow>
<mml:mi>i</mml:mi>
<mml:mo>&#x2a;</mml:mo>
</mml:msubsup>
</mml:mrow>
</mml:math>
</inline-formula>, TRC retrieves the corresponding information <inline-formula id="inf55">
<mml:math id="m63">
<mml:mrow>
<mml:mfenced open="(" close=")" separators="|">
<mml:mrow>
<mml:mi>I</mml:mi>
<mml:msub>
<mml:mi>D</mml:mi>
<mml:mi>i</mml:mi>
</mml:msub>
<mml:mo>,</mml:mo>
<mml:msub>
<mml:mi>A</mml:mi>
<mml:mi>i</mml:mi>
</mml:msub>
</mml:mrow>
</mml:mfenced>
</mml:mrow>
</mml:math>
</inline-formula> from the database and computes the message <inline-formula id="inf56">
<mml:math id="m64">
<mml:mrow>
<mml:mfenced open="(" close=")" separators="|">
<mml:mrow>
<mml:msub>
<mml:mi>y</mml:mi>
<mml:mi>i</mml:mi>
</mml:msub>
<mml:mo>&#x2a;</mml:mo>
<mml:mo>,</mml:mo>
<mml:msubsup>
<mml:mrow>
<mml:mi>S</mml:mi>
<mml:mi>I</mml:mi>
<mml:mi>D</mml:mi>
</mml:mrow>
<mml:mi>j</mml:mi>
<mml:mo>&#x2a;</mml:mo>
</mml:msubsup>
</mml:mrow>
</mml:mfenced>
</mml:mrow>
</mml:math>
</inline-formula>.</p>
</list-item>
</list>
<disp-formula id="equ7">
<mml:math id="m65">
<mml:mrow>
<mml:msubsup>
<mml:mi mathvariant="normal">y</mml:mi>
<mml:mi>i</mml:mi>
<mml:mo>&#x2a;</mml:mo>
</mml:msubsup>
<mml:mo>&#x3d;</mml:mo>
<mml:mi>H</mml:mi>
<mml:mrow>
<mml:mfenced open="(" close=")" separators="|">
<mml:mrow>
<mml:msubsup>
<mml:mrow>
<mml:mi>P</mml:mi>
<mml:mi>I</mml:mi>
<mml:mi>D</mml:mi>
</mml:mrow>
<mml:mi>i</mml:mi>
<mml:mo>&#x2a;</mml:mo>
</mml:msubsup>
<mml:mo>,</mml:mo>
<mml:msubsup>
<mml:mi mathvariant="normal">V</mml:mi>
<mml:mn>2</mml:mn>
<mml:mo>&#x2a;</mml:mo>
</mml:msubsup>
<mml:mo>,</mml:mo>
<mml:msub>
<mml:mi>T</mml:mi>
<mml:mn>1</mml:mn>
</mml:msub>
</mml:mrow>
</mml:mfenced>
</mml:mrow>
<mml:mo>&#x2295;</mml:mo>
<mml:msub>
<mml:mi>V</mml:mi>
<mml:mn>4</mml:mn>
</mml:msub>
</mml:mrow>
</mml:math>
</disp-formula>
<disp-formula id="equ8">
<mml:math id="m66">
<mml:mrow>
<mml:msubsup>
<mml:mrow>
<mml:mi>S</mml:mi>
<mml:mi>I</mml:mi>
<mml:mi>D</mml:mi>
</mml:mrow>
<mml:mi>j</mml:mi>
<mml:mo>&#x2a;</mml:mo>
</mml:msubsup>
<mml:mo>&#x3d;</mml:mo>
<mml:mi>H</mml:mi>
<mml:mrow>
<mml:mfenced open="(" close=")" separators="|">
<mml:mrow>
<mml:msubsup>
<mml:mrow>
<mml:mi>P</mml:mi>
<mml:mi>I</mml:mi>
<mml:mi>D</mml:mi>
</mml:mrow>
<mml:mi>i</mml:mi>
<mml:mo>&#x2a;</mml:mo>
</mml:msubsup>
<mml:mo>,</mml:mo>
<mml:msubsup>
<mml:mi mathvariant="normal">V</mml:mi>
<mml:mn>2</mml:mn>
<mml:mo>&#x2a;</mml:mo>
</mml:msubsup>
<mml:mo>,</mml:mo>
<mml:msubsup>
<mml:mi mathvariant="normal">y</mml:mi>
<mml:mi>i</mml:mi>
<mml:mo>&#x2a;</mml:mo>
</mml:msubsup>
<mml:mo>,</mml:mo>
<mml:msub>
<mml:mi>T</mml:mi>
<mml:mn>1</mml:mn>
</mml:msub>
</mml:mrow>
</mml:mfenced>
</mml:mrow>
<mml:mo>&#x2295;</mml:mo>
<mml:msub>
<mml:mi>V</mml:mi>
<mml:mn>5</mml:mn>
</mml:msub>
</mml:mrow>
</mml:math>
</disp-formula>
<p>TRC further computes the verification message <inline-formula id="inf57">
<mml:math id="m67">
<mml:mrow>
<mml:msubsup>
<mml:mi mathvariant="normal">V</mml:mi>
<mml:mn>6</mml:mn>
<mml:mo>&#x2a;</mml:mo>
</mml:msubsup>
</mml:mrow>
</mml:math>
</inline-formula> using the message <inline-formula id="inf58">
<mml:math id="m68">
<mml:mrow>
<mml:mfenced open="(" close=")" separators="|">
<mml:mrow>
<mml:msub>
<mml:mi>y</mml:mi>
<mml:mi>i</mml:mi>
</mml:msub>
<mml:mo>&#x2a;</mml:mo>
<mml:mo>,</mml:mo>
<mml:msubsup>
<mml:mrow>
<mml:mi>S</mml:mi>
<mml:mi>I</mml:mi>
<mml:mi>D</mml:mi>
</mml:mrow>
<mml:mi>j</mml:mi>
<mml:mo>&#x2a;</mml:mo>
</mml:msubsup>
</mml:mrow>
</mml:mfenced>
</mml:mrow>
</mml:math>
</inline-formula>:<disp-formula id="equ9">
<mml:math id="m69">
<mml:mrow>
<mml:msubsup>
<mml:mi mathvariant="normal">V</mml:mi>
<mml:mn>6</mml:mn>
<mml:mo>&#x2a;</mml:mo>
</mml:msubsup>
<mml:mo>&#x3d;</mml:mo>
<mml:mi>H</mml:mi>
<mml:mrow>
<mml:mfenced open="(" close=")" separators="|">
<mml:mrow>
<mml:msubsup>
<mml:mrow>
<mml:mi>S</mml:mi>
<mml:mi>I</mml:mi>
<mml:mi>D</mml:mi>
</mml:mrow>
<mml:mi>j</mml:mi>
<mml:mo>&#x2a;</mml:mo>
</mml:msubsup>
<mml:mo>,</mml:mo>
<mml:mi>I</mml:mi>
<mml:msub>
<mml:mi>D</mml:mi>
<mml:mi>i</mml:mi>
</mml:msub>
<mml:mo>,</mml:mo>
<mml:msubsup>
<mml:mi mathvariant="normal">V</mml:mi>
<mml:mn>2</mml:mn>
<mml:mo>&#x2a;</mml:mo>
</mml:msubsup>
<mml:mo>,</mml:mo>
<mml:msubsup>
<mml:mi mathvariant="normal">y</mml:mi>
<mml:mi>i</mml:mi>
<mml:mo>&#x2a;</mml:mo>
</mml:msubsup>
<mml:mo>,</mml:mo>
<mml:msub>
<mml:mi>A</mml:mi>
<mml:mi>i</mml:mi>
</mml:msub>
<mml:mo>,</mml:mo>
<mml:msub>
<mml:mi>T</mml:mi>
<mml:mn>1</mml:mn>
</mml:msub>
</mml:mrow>
</mml:mfenced>
</mml:mrow>
</mml:mrow>
</mml:math>
</disp-formula>
</p>
<p>TRC verifies the correctness of the message <inline-formula id="inf59">
<mml:math id="m70">
<mml:mrow>
<mml:msub>
<mml:mi>V</mml:mi>
<mml:mi>6</mml:mi>
</mml:msub>
<mml:mo>&#x2a;</mml:mo>
<mml:mo>&#x3d;</mml:mo>
<mml:msub>
<mml:mi>V</mml:mi>
<mml:mn>6</mml:mn>
</mml:msub>
</mml:mrow>
</mml:math>
</inline-formula>. If the message is validated, the TRC can authenticate that the communication requester is <inline-formula id="inf60">
<mml:math id="m71">
<mml:mrow>
<mml:msub>
<mml:mi>U</mml:mi>
<mml:mi>i</mml:mi>
</mml:msub>
</mml:mrow>
</mml:math>
</inline-formula>. Otherwise, TRC rejects the authentication request. TRC retrieves the corresponding information <inline-formula id="inf61">
<mml:math id="m72">
<mml:mrow>
<mml:mi>I</mml:mi>
<mml:msub>
<mml:mi>D</mml:mi>
<mml:mi>j</mml:mi>
</mml:msub>
</mml:mrow>
</mml:math>
</inline-formula> from the database using the pseudonym <inline-formula id="inf62">
<mml:math id="m73">
<mml:mrow>
<mml:msubsup>
<mml:mrow>
<mml:mi>S</mml:mi>
<mml:mi>I</mml:mi>
<mml:mi>D</mml:mi>
</mml:mrow>
<mml:mi>j</mml:mi>
<mml:mo>&#x2a;</mml:mo>
</mml:msubsup>
</mml:mrow>
</mml:math>
</inline-formula>, selects the current timestamp <inline-formula id="inf63">
<mml:math id="m74">
<mml:mrow>
<mml:msub>
<mml:mi>T</mml:mi>
<mml:mn>2</mml:mn>
</mml:msub>
</mml:mrow>
</mml:math>
</inline-formula>, computes <inline-formula id="inf64">
<mml:math id="m75">
<mml:mrow>
<mml:msub>
<mml:mi>B</mml:mi>
<mml:mi>j</mml:mi>
</mml:msub>
<mml:mo>&#x2a;</mml:mo>
<mml:mo>&#x3d;</mml:mo>
<mml:mi>H</mml:mi>
<mml:mrow>
<mml:mfenced open="(" close=")" separators="|">
<mml:mrow>
<mml:mi>I</mml:mi>
<mml:msub>
<mml:mi>D</mml:mi>
<mml:mi>j</mml:mi>
</mml:msub>
<mml:mo>,</mml:mo>
<mml:mi>s</mml:mi>
</mml:mrow>
</mml:mfenced>
</mml:mrow>
</mml:mrow>
</mml:math>
</inline-formula>, and generates the message <inline-formula id="inf65">
<mml:math id="m76">
<mml:mrow>
<mml:mfenced open="{" close="}" separators="|">
<mml:mrow>
<mml:msubsup>
<mml:mrow>
<mml:mi>S</mml:mi>
<mml:mi>I</mml:mi>
<mml:mi>D</mml:mi>
</mml:mrow>
<mml:mi>j</mml:mi>
<mml:mo>&#x2a;</mml:mo>
</mml:msubsup>
<mml:mo>,</mml:mo>
<mml:msub>
<mml:mi>V</mml:mi>
<mml:mn>1</mml:mn>
</mml:msub>
<mml:mo>,</mml:mo>
<mml:msub>
<mml:mi>V</mml:mi>
<mml:mn>7</mml:mn>
</mml:msub>
<mml:mo>,</mml:mo>
<mml:msub>
<mml:mi>V</mml:mi>
<mml:mn>8</mml:mn>
</mml:msub>
<mml:mo>,</mml:mo>
<mml:msub>
<mml:mi>V</mml:mi>
<mml:mn>9</mml:mn>
</mml:msub>
<mml:mo>,</mml:mo>
<mml:msub>
<mml:mi>T</mml:mi>
<mml:mn>2</mml:mn>
</mml:msub>
</mml:mrow>
</mml:mfenced>
</mml:mrow>
</mml:math>
</inline-formula>. TRC sends the message <inline-formula id="inf66">
<mml:math id="m77">
<mml:mrow>
<mml:mfenced open="{" close="}" separators="|">
<mml:mrow>
<mml:msub>
<mml:mrow>
<mml:msubsup>
<mml:mrow>
<mml:mi>S</mml:mi>
<mml:mi>I</mml:mi>
<mml:mi>D</mml:mi>
</mml:mrow>
<mml:mi>j</mml:mi>
<mml:mo>&#x2a;</mml:mo>
</mml:msubsup>
<mml:mo>,</mml:mo>
<mml:mi>V</mml:mi>
</mml:mrow>
<mml:mn>1</mml:mn>
</mml:msub>
<mml:mo>,</mml:mo>
<mml:msub>
<mml:mi>V</mml:mi>
<mml:mn>7</mml:mn>
</mml:msub>
<mml:mo>,</mml:mo>
<mml:msub>
<mml:mi>V</mml:mi>
<mml:mn>8</mml:mn>
</mml:msub>
<mml:mo>,</mml:mo>
<mml:msub>
<mml:mi>V</mml:mi>
<mml:mn>9</mml:mn>
</mml:msub>
<mml:mo>,</mml:mo>
<mml:msub>
<mml:mi>T</mml:mi>
<mml:mn>1</mml:mn>
</mml:msub>
</mml:mrow>
</mml:mfenced>
</mml:mrow>
</mml:math>
</inline-formula> to <inline-formula id="inf67">
<mml:math id="m78">
<mml:mrow>
<mml:msub>
<mml:mrow>
<mml:mi>S</mml:mi>
<mml:mi>C</mml:mi>
</mml:mrow>
<mml:mi>j</mml:mi>
</mml:msub>
</mml:mrow>
</mml:math>
</inline-formula> via a public channel.<disp-formula id="equ10">
<mml:math id="m79">
<mml:mrow>
<mml:msub>
<mml:mi>V</mml:mi>
<mml:mn>7</mml:mn>
</mml:msub>
<mml:mo>&#x3d;</mml:mo>
<mml:msub>
<mml:mi mathvariant="normal">T</mml:mi>
<mml:mrow>
<mml:msubsup>
<mml:mi mathvariant="normal">B</mml:mi>
<mml:mi>j</mml:mi>
<mml:mo>&#x2a;</mml:mo>
</mml:msubsup>
<mml:mi>s</mml:mi>
</mml:mrow>
</mml:msub>
<mml:mrow>
<mml:mfenced open="(" close=")" separators="|">
<mml:mrow>
<mml:mi>x</mml:mi>
</mml:mrow>
</mml:mfenced>
</mml:mrow>
<mml:mtext>&#x2009;</mml:mtext>
<mml:mi mathvariant="italic">mod</mml:mi>
<mml:mtext>&#x2009;</mml:mtext>
<mml:mi>p</mml:mi>
</mml:mrow>
</mml:math>
</disp-formula>
<disp-formula id="equ11">
<mml:math id="m80">
<mml:mrow>
<mml:msub>
<mml:mi>V</mml:mi>
<mml:mn>8</mml:mn>
</mml:msub>
<mml:mo>&#x3d;</mml:mo>
<mml:mi>H</mml:mi>
<mml:mrow>
<mml:mfenced open="(" close=")" separators="|">
<mml:mrow>
<mml:msub>
<mml:mi>V</mml:mi>
<mml:mn>7</mml:mn>
</mml:msub>
<mml:mo>,</mml:mo>
<mml:msub>
<mml:mi>T</mml:mi>
<mml:mn>2</mml:mn>
</mml:msub>
</mml:mrow>
</mml:mfenced>
</mml:mrow>
<mml:mo>&#x2295;</mml:mo>
<mml:msubsup>
<mml:mrow>
<mml:mi>P</mml:mi>
<mml:mi>I</mml:mi>
<mml:mi>D</mml:mi>
</mml:mrow>
<mml:mi>i</mml:mi>
<mml:mo>&#x2a;</mml:mo>
</mml:msubsup>
</mml:mrow>
</mml:math>
</disp-formula>
<disp-formula id="equ12">
<mml:math id="m81">
<mml:mrow>
<mml:msub>
<mml:mi>V</mml:mi>
<mml:mn>9</mml:mn>
</mml:msub>
<mml:mo>&#x3d;</mml:mo>
<mml:mi>H</mml:mi>
<mml:mrow>
<mml:mfenced open="(" close=")" separators="|">
<mml:mrow>
<mml:msubsup>
<mml:mrow>
<mml:mi>P</mml:mi>
<mml:mi>I</mml:mi>
<mml:mi>D</mml:mi>
</mml:mrow>
<mml:mi>i</mml:mi>
<mml:mo>&#x2a;</mml:mo>
</mml:msubsup>
<mml:mo>,</mml:mo>
<mml:mi>I</mml:mi>
<mml:msub>
<mml:mi>D</mml:mi>
<mml:mi>j</mml:mi>
</mml:msub>
<mml:mo>,</mml:mo>
<mml:msubsup>
<mml:mrow>
<mml:mi>S</mml:mi>
<mml:mi>I</mml:mi>
<mml:mi>D</mml:mi>
</mml:mrow>
<mml:mi>j</mml:mi>
<mml:mo>&#x2a;</mml:mo>
</mml:msubsup>
<mml:mo>,</mml:mo>
<mml:msubsup>
<mml:mi mathvariant="normal">B</mml:mi>
<mml:mi>j</mml:mi>
<mml:mo>&#x2a;</mml:mo>
</mml:msubsup>
<mml:mo>,</mml:mo>
<mml:msub>
<mml:mi>T</mml:mi>
<mml:mn>2</mml:mn>
</mml:msub>
</mml:mrow>
</mml:mfenced>
</mml:mrow>
</mml:mrow>
</mml:math>
</disp-formula>
<list list-type="simple">
<list-item>
<p>3. Upon receiving the message <inline-formula id="inf68">
<mml:math id="m82">
<mml:mrow>
<mml:mfenced open="{" close="}" separators="|">
<mml:mrow>
<mml:msubsup>
<mml:mrow>
<mml:mi>S</mml:mi>
<mml:mi>I</mml:mi>
<mml:mi>D</mml:mi>
</mml:mrow>
<mml:mi>j</mml:mi>
<mml:mo>&#x2a;</mml:mo>
</mml:msubsup>
<mml:mo>,</mml:mo>
<mml:msub>
<mml:mi>V</mml:mi>
<mml:mn>1</mml:mn>
</mml:msub>
<mml:mo>,</mml:mo>
<mml:msub>
<mml:mi>V</mml:mi>
<mml:mn>7</mml:mn>
</mml:msub>
<mml:mo>,</mml:mo>
<mml:msub>
<mml:mi>V</mml:mi>
<mml:mn>8</mml:mn>
</mml:msub>
<mml:mo>,</mml:mo>
<mml:msub>
<mml:mi>V</mml:mi>
<mml:mn>9</mml:mn>
</mml:msub>
<mml:mo>,</mml:mo>
<mml:msub>
<mml:mi>T</mml:mi>
<mml:mn>1</mml:mn>
</mml:msub>
</mml:mrow>
</mml:mfenced>
</mml:mrow>
</mml:math>
</inline-formula> from TRC, <inline-formula id="inf69">
<mml:math id="m83">
<mml:mrow>
<mml:msub>
<mml:mrow>
<mml:mi>S</mml:mi>
<mml:mi>C</mml:mi>
</mml:mrow>
<mml:mi>j</mml:mi>
</mml:msub>
</mml:mrow>
</mml:math>
</inline-formula> first verifies <inline-formula id="inf70">
<mml:math id="m84">
<mml:mrow>
<mml:msub>
<mml:mi>T</mml:mi>
<mml:mn>2</mml:mn>
</mml:msub>
</mml:mrow>
</mml:math>
</inline-formula>. Then <inline-formula id="inf71">
<mml:math id="m85">
<mml:mrow>
<mml:msub>
<mml:mrow>
<mml:mi>S</mml:mi>
<mml:mi>C</mml:mi>
</mml:mrow>
<mml:mi>j</mml:mi>
</mml:msub>
</mml:mrow>
</mml:math>
</inline-formula> retrieves the corresponding information <inline-formula id="inf72">
<mml:math id="m86">
<mml:mrow>
<mml:msub>
<mml:mi>B</mml:mi>
<mml:mi>j</mml:mi>
</mml:msub>
</mml:mrow>
</mml:math>
</inline-formula> from the database using <inline-formula id="inf73">
<mml:math id="m87">
<mml:mrow>
<mml:msubsup>
<mml:mrow>
<mml:mi>S</mml:mi>
<mml:mi>I</mml:mi>
<mml:mi>D</mml:mi>
</mml:mrow>
<mml:mi>j</mml:mi>
<mml:mo>&#x2a;</mml:mo>
</mml:msubsup>
</mml:mrow>
</mml:math>
</inline-formula> and computes the message:</p>
</list-item>
</list>
<disp-formula id="equ13">
<mml:math id="m88">
<mml:mrow>
<mml:msubsup>
<mml:mi mathvariant="normal">V</mml:mi>
<mml:mn>7</mml:mn>
<mml:mo>&#x2a;</mml:mo>
</mml:msubsup>
<mml:mo>&#x3d;</mml:mo>
<mml:msub>
<mml:mi mathvariant="normal">T</mml:mi>
<mml:msub>
<mml:mi>B</mml:mi>
<mml:mi>j</mml:mi>
</mml:msub>
</mml:msub>
<mml:mrow>
<mml:mfenced open="(" close=")" separators="|">
<mml:mrow>
<mml:msub>
<mml:mi>S</mml:mi>
<mml:mrow>
<mml:mi>p</mml:mi>
<mml:mi>u</mml:mi>
<mml:mi>b</mml:mi>
</mml:mrow>
</mml:msub>
</mml:mrow>
</mml:mfenced>
</mml:mrow>
<mml:mtext>&#x2009;</mml:mtext>
<mml:mi mathvariant="italic">mod</mml:mi>
<mml:mtext>&#x2009;</mml:mtext>
<mml:mi>p</mml:mi>
</mml:mrow>
</mml:math>
</disp-formula>
<disp-formula id="equ14">
<mml:math id="m89">
<mml:mrow>
<mml:msubsup>
<mml:mrow>
<mml:mi>P</mml:mi>
<mml:mi>I</mml:mi>
<mml:mi>D</mml:mi>
</mml:mrow>
<mml:mi>i</mml:mi>
<mml:mo>&#x2032;</mml:mo>
</mml:msubsup>
<mml:mo>&#x3d;</mml:mo>
<mml:mi>H</mml:mi>
<mml:mrow>
<mml:mfenced open="(" close=")" separators="|">
<mml:mrow>
<mml:msub>
<mml:mi>V</mml:mi>
<mml:mn>7</mml:mn>
</mml:msub>
<mml:mo>,</mml:mo>
<mml:msub>
<mml:mi>T</mml:mi>
<mml:mn>2</mml:mn>
</mml:msub>
</mml:mrow>
</mml:mfenced>
</mml:mrow>
<mml:mo>&#x2295;</mml:mo>
<mml:msub>
<mml:mi>V</mml:mi>
<mml:mn>8</mml:mn>
</mml:msub>
</mml:mrow>
</mml:math>
</disp-formula>
</p>
<p>
<inline-formula id="inf74">
<mml:math id="m90">
<mml:mrow>
<mml:msub>
<mml:mrow>
<mml:mi>S</mml:mi>
<mml:mi>C</mml:mi>
</mml:mrow>
<mml:mi>j</mml:mi>
</mml:msub>
</mml:mrow>
</mml:math>
</inline-formula> calculates the verification message <inline-formula id="inf75">
<mml:math id="m91">
<mml:mrow>
<mml:msubsup>
<mml:mi mathvariant="normal">V</mml:mi>
<mml:mn>9</mml:mn>
<mml:mo>&#x2a;</mml:mo>
</mml:msubsup>
</mml:mrow>
</mml:math>
</inline-formula> using the retrieved information.<disp-formula id="equ15">
<mml:math id="m92">
<mml:mrow>
<mml:msubsup>
<mml:mi mathvariant="normal">V</mml:mi>
<mml:mn>9</mml:mn>
<mml:mo>&#x2a;</mml:mo>
</mml:msubsup>
<mml:mo>&#x3d;</mml:mo>
<mml:mi>H</mml:mi>
<mml:mrow>
<mml:mfenced open="(" close=")" separators="|">
<mml:mrow>
<mml:msubsup>
<mml:mrow>
<mml:mi>P</mml:mi>
<mml:mi>I</mml:mi>
<mml:mi>D</mml:mi>
</mml:mrow>
<mml:mi>i</mml:mi>
<mml:mo>&#x2032;</mml:mo>
</mml:msubsup>
<mml:mo>,</mml:mo>
<mml:mi>I</mml:mi>
<mml:msub>
<mml:mi>D</mml:mi>
<mml:mi>j</mml:mi>
</mml:msub>
<mml:mo>,</mml:mo>
<mml:mi>S</mml:mi>
<mml:mi>I</mml:mi>
<mml:msub>
<mml:mi>D</mml:mi>
<mml:mi>j</mml:mi>
</mml:msub>
<mml:mo>,</mml:mo>
<mml:msub>
<mml:mi>B</mml:mi>
<mml:mi>j</mml:mi>
</mml:msub>
<mml:mo>,</mml:mo>
<mml:msub>
<mml:mi>T</mml:mi>
<mml:mn>2</mml:mn>
</mml:msub>
</mml:mrow>
</mml:mfenced>
</mml:mrow>
</mml:mrow>
</mml:math>
</disp-formula>
<list list-type="simple">
<list-item>
<p>4. <inline-formula id="inf76">
<mml:math id="m93">
<mml:mrow>
<mml:msub>
<mml:mrow>
<mml:mi>S</mml:mi>
<mml:mi>C</mml:mi>
</mml:mrow>
<mml:mi>j</mml:mi>
</mml:msub>
</mml:mrow>
</mml:math>
</inline-formula> first verifies the correctness of the message <inline-formula id="inf77">
<mml:math id="m94">
<mml:mrow>
<mml:msubsup>
<mml:mi mathvariant="normal">V</mml:mi>
<mml:mn>9</mml:mn>
<mml:mo>&#x2a;</mml:mo>
</mml:msubsup>
<mml:mo>&#x3d;</mml:mo>
<mml:msub>
<mml:mi>V</mml:mi>
<mml:mn>9</mml:mn>
</mml:msub>
</mml:mrow>
</mml:math>
</inline-formula>. If the message fails verification, <inline-formula id="inf78">
<mml:math id="m95">
<mml:mrow>
<mml:msub>
<mml:mrow>
<mml:mi>S</mml:mi>
<mml:mi>C</mml:mi>
</mml:mrow>
<mml:mi>j</mml:mi>
</mml:msub>
</mml:mrow>
</mml:math>
</inline-formula> rejects the communication request. Otherwise, <inline-formula id="inf79">
<mml:math id="m96">
<mml:mrow>
<mml:msub>
<mml:mrow>
<mml:mi>S</mml:mi>
<mml:mi>C</mml:mi>
</mml:mrow>
<mml:mi>j</mml:mi>
</mml:msub>
</mml:mrow>
</mml:math>
</inline-formula> can authenticate that the communication requester is the TRC. <inline-formula id="inf80">
<mml:math id="m97">
<mml:mrow>
<mml:msub>
<mml:mrow>
<mml:mi>S</mml:mi>
<mml:mi>C</mml:mi>
</mml:mrow>
<mml:mi>j</mml:mi>
</mml:msub>
</mml:mrow>
</mml:math>
</inline-formula> then selects a random number <inline-formula id="inf81">
<mml:math id="m98">
<mml:mrow>
<mml:msub>
<mml:mi>e</mml:mi>
<mml:mi>j</mml:mi>
</mml:msub>
</mml:mrow>
</mml:math>
</inline-formula> and the current timestamp <inline-formula id="inf82">
<mml:math id="m99">
<mml:mrow>
<mml:msub>
<mml:mi>T</mml:mi>
<mml:mn>3</mml:mn>
</mml:msub>
</mml:mrow>
</mml:math>
</inline-formula>, calculates the message <inline-formula id="inf83">
<mml:math id="m100">
<mml:mrow>
<mml:mfenced open="(" close=")" separators="|">
<mml:mrow>
<mml:msub>
<mml:mi>V</mml:mi>
<mml:mn>10</mml:mn>
</mml:msub>
<mml:mo>,</mml:mo>
<mml:msub>
<mml:mi>V</mml:mi>
<mml:mn>11</mml:mn>
</mml:msub>
<mml:mo>,</mml:mo>
<mml:mi>S</mml:mi>
<mml:msub>
<mml:mi>K</mml:mi>
<mml:mi>j</mml:mi>
</mml:msub>
<mml:mo>,</mml:mo>
<mml:msub>
<mml:mi>V</mml:mi>
<mml:mn>12</mml:mn>
</mml:msub>
</mml:mrow>
</mml:mfenced>
</mml:mrow>
</mml:math>
</inline-formula> and sends the message <inline-formula id="inf84">
<mml:math id="m101">
<mml:mrow>
<mml:mfenced open="{" close="}" separators="|">
<mml:mrow>
<mml:msub>
<mml:mi>V</mml:mi>
<mml:mn>10</mml:mn>
</mml:msub>
<mml:mo>,</mml:mo>
<mml:msub>
<mml:mi>V</mml:mi>
<mml:mn>12</mml:mn>
</mml:msub>
<mml:mo>,</mml:mo>
<mml:msub>
<mml:mi>T</mml:mi>
<mml:mn>3</mml:mn>
</mml:msub>
</mml:mrow>
</mml:mfenced>
</mml:mrow>
</mml:math>
</inline-formula> to <inline-formula id="inf85">
<mml:math id="m102">
<mml:mrow>
<mml:msub>
<mml:mi>U</mml:mi>
<mml:mrow>
<mml:mi>i</mml:mi>
<mml:mtext>&#x2009;</mml:mtext>
</mml:mrow>
</mml:msub>
</mml:mrow>
</mml:math>
</inline-formula> via a public channel.</p>
</list-item>
</list>
<disp-formula id="equ16">
<mml:math id="m103">
<mml:mrow>
<mml:msub>
<mml:mi>V</mml:mi>
<mml:mn>10</mml:mn>
</mml:msub>
<mml:mo>&#x3d;</mml:mo>
<mml:msub>
<mml:mi mathvariant="normal">T</mml:mi>
<mml:msub>
<mml:mi>e</mml:mi>
<mml:mi>j</mml:mi>
</mml:msub>
</mml:msub>
<mml:mrow>
<mml:mfenced open="(" close=")" separators="|">
<mml:mrow>
<mml:mi>x</mml:mi>
</mml:mrow>
</mml:mfenced>
</mml:mrow>
<mml:mtext>&#x2009;</mml:mtext>
<mml:mi mathvariant="italic">mod</mml:mi>
<mml:mtext>&#x2009;</mml:mtext>
<mml:mi>p</mml:mi>
</mml:mrow>
</mml:math>
</disp-formula>
<disp-formula id="equ17">
<mml:math id="m104">
<mml:mrow>
<mml:msub>
<mml:mi>V</mml:mi>
<mml:mn>11</mml:mn>
</mml:msub>
<mml:mo>&#x3d;</mml:mo>
<mml:msub>
<mml:mi mathvariant="normal">T</mml:mi>
<mml:msub>
<mml:mi>e</mml:mi>
<mml:mi>j</mml:mi>
</mml:msub>
</mml:msub>
<mml:mrow>
<mml:mfenced open="(" close=")" separators="|">
<mml:mrow>
<mml:msub>
<mml:mi>V</mml:mi>
<mml:mn>1</mml:mn>
</mml:msub>
</mml:mrow>
</mml:mfenced>
</mml:mrow>
<mml:mtext>&#x2009;</mml:mtext>
<mml:mi mathvariant="italic">mod</mml:mi>
<mml:mtext>&#x2009;</mml:mtext>
<mml:mi>p</mml:mi>
</mml:mrow>
</mml:math>
</disp-formula>
<disp-formula id="equ18">
<mml:math id="m105">
<mml:mrow>
<mml:mi>S</mml:mi>
<mml:msub>
<mml:mi>K</mml:mi>
<mml:mi>j</mml:mi>
</mml:msub>
<mml:mo>&#x3d;</mml:mo>
<mml:mi>H</mml:mi>
<mml:mrow>
<mml:mfenced open="(" close=")" separators="|">
<mml:mrow>
<mml:msubsup>
<mml:mrow>
<mml:mi>P</mml:mi>
<mml:mi>I</mml:mi>
<mml:mi>D</mml:mi>
</mml:mrow>
<mml:mi>i</mml:mi>
<mml:mo>&#x2032;</mml:mo>
</mml:msubsup>
<mml:mo>,</mml:mo>
<mml:msub>
<mml:mrow>
<mml:mi>S</mml:mi>
<mml:mi>I</mml:mi>
<mml:msub>
<mml:mi>D</mml:mi>
<mml:mi>j</mml:mi>
</mml:msub>
<mml:mo>,</mml:mo>
<mml:mi>V</mml:mi>
</mml:mrow>
<mml:mn>11</mml:mn>
</mml:msub>
<mml:mo>,</mml:mo>
<mml:msub>
<mml:mi>T</mml:mi>
<mml:mn>3</mml:mn>
</mml:msub>
</mml:mrow>
</mml:mfenced>
</mml:mrow>
</mml:mrow>
</mml:math>
</disp-formula>
<disp-formula id="equ19">
<mml:math id="m106">
<mml:mrow>
<mml:msub>
<mml:mi>V</mml:mi>
<mml:mn>12</mml:mn>
</mml:msub>
<mml:mo>&#x3d;</mml:mo>
<mml:mi>H</mml:mi>
<mml:mrow>
<mml:mfenced open="(" close=")" separators="|">
<mml:mrow>
<mml:msubsup>
<mml:mrow>
<mml:mi>P</mml:mi>
<mml:mi>I</mml:mi>
<mml:mi>D</mml:mi>
</mml:mrow>
<mml:mi>i</mml:mi>
<mml:mo>&#x2032;</mml:mo>
</mml:msubsup>
<mml:mo>,</mml:mo>
<mml:msub>
<mml:mi>V</mml:mi>
<mml:mn>10</mml:mn>
</mml:msub>
<mml:mo>,</mml:mo>
<mml:mi>S</mml:mi>
<mml:mi>I</mml:mi>
<mml:msub>
<mml:mi>D</mml:mi>
<mml:mi>j</mml:mi>
</mml:msub>
<mml:mo>,</mml:mo>
<mml:msub>
<mml:mi>V</mml:mi>
<mml:mn>11</mml:mn>
</mml:msub>
<mml:mo>,</mml:mo>
<mml:mi>S</mml:mi>
<mml:msub>
<mml:mi>K</mml:mi>
<mml:mi>j</mml:mi>
</mml:msub>
<mml:mo>,</mml:mo>
<mml:msub>
<mml:mi>T</mml:mi>
<mml:mn>3</mml:mn>
</mml:msub>
</mml:mrow>
</mml:mfenced>
</mml:mrow>
</mml:mrow>
</mml:math>
</disp-formula>
<list list-type="simple">
<list-item>
<p>5. Upon receiving <inline-formula id="inf86">
<mml:math id="m107">
<mml:mrow>
<mml:mfenced open="{" close="}" separators="|">
<mml:mrow>
<mml:msub>
<mml:mi>V</mml:mi>
<mml:mn>10</mml:mn>
</mml:msub>
<mml:mo>,</mml:mo>
<mml:msub>
<mml:mi>V</mml:mi>
<mml:mn>12</mml:mn>
</mml:msub>
<mml:mo>,</mml:mo>
<mml:msub>
<mml:mi>T</mml:mi>
<mml:mn>3</mml:mn>
</mml:msub>
</mml:mrow>
</mml:mfenced>
</mml:mrow>
</mml:math>
</inline-formula>, <inline-formula id="inf87">
<mml:math id="m108">
<mml:mrow>
<mml:msub>
<mml:mi>U</mml:mi>
<mml:mi>i</mml:mi>
</mml:msub>
</mml:mrow>
</mml:math>
</inline-formula> first verifies <inline-formula id="inf88">
<mml:math id="m109">
<mml:mrow>
<mml:msub>
<mml:mi>T</mml:mi>
<mml:mn>3</mml:mn>
</mml:msub>
</mml:mrow>
</mml:math>
</inline-formula>. If the received authentication request message is valid, <inline-formula id="inf89">
<mml:math id="m110">
<mml:mrow>
<mml:msub>
<mml:mi>U</mml:mi>
<mml:mi>i</mml:mi>
</mml:msub>
</mml:mrow>
</mml:math>
</inline-formula> proceeds to the next step; otherwise, <inline-formula id="inf90">
<mml:math id="m111">
<mml:mrow>
<mml:msub>
<mml:mi>U</mml:mi>
<mml:mi>i</mml:mi>
</mml:msub>
</mml:mrow>
</mml:math>
</inline-formula> rejects the authentication request. <inline-formula id="inf91">
<mml:math id="m112">
<mml:mrow>
<mml:msub>
<mml:mi>U</mml:mi>
<mml:mi>i</mml:mi>
</mml:msub>
</mml:mrow>
</mml:math>
</inline-formula> calculates the session key using the received message <inline-formula id="inf92">
<mml:math id="m113">
<mml:mrow>
<mml:msub>
<mml:mi>V</mml:mi>
<mml:mn>10</mml:mn>
</mml:msub>
</mml:mrow>
</mml:math>
</inline-formula>.</p>
</list-item>
</list>
<disp-formula id="equ20">
<mml:math id="m114">
<mml:mrow>
<mml:msubsup>
<mml:mi mathvariant="normal">V</mml:mi>
<mml:mn>11</mml:mn>
<mml:mo>&#x2a;</mml:mo>
</mml:msubsup>
<mml:mo>&#x3d;</mml:mo>
<mml:msub>
<mml:mi mathvariant="normal">T</mml:mi>
<mml:msub>
<mml:mi>c</mml:mi>
<mml:mi>i</mml:mi>
</mml:msub>
</mml:msub>
<mml:mrow>
<mml:mfenced open="(" close=")" separators="|">
<mml:mrow>
<mml:msub>
<mml:mi>V</mml:mi>
<mml:mn>10</mml:mn>
</mml:msub>
</mml:mrow>
</mml:mfenced>
</mml:mrow>
<mml:mtext>&#x2009;</mml:mtext>
<mml:mi mathvariant="italic">mod</mml:mi>
<mml:mtext>&#x2009;</mml:mtext>
<mml:mi>p</mml:mi>
</mml:mrow>
</mml:math>
</disp-formula>
<disp-formula id="equ21">
<mml:math id="m115">
<mml:mrow>
<mml:mi>S</mml:mi>
<mml:msub>
<mml:mi>K</mml:mi>
<mml:mi>i</mml:mi>
</mml:msub>
<mml:mo>&#x3d;</mml:mo>
<mml:mi>H</mml:mi>
<mml:mrow>
<mml:mfenced open="(" close=")" separators="|">
<mml:mrow>
<mml:mi>P</mml:mi>
<mml:mi>I</mml:mi>
<mml:msub>
<mml:mi>D</mml:mi>
<mml:mi>i</mml:mi>
</mml:msub>
<mml:mo>,</mml:mo>
<mml:mi>S</mml:mi>
<mml:mi>I</mml:mi>
<mml:msub>
<mml:mi>D</mml:mi>
<mml:mi>j</mml:mi>
</mml:msub>
<mml:mo>,</mml:mo>
<mml:msubsup>
<mml:mi mathvariant="normal">V</mml:mi>
<mml:mn>11</mml:mn>
<mml:mo>&#x2a;</mml:mo>
</mml:msubsup>
<mml:mo>,</mml:mo>
<mml:msub>
<mml:mi>T</mml:mi>
<mml:mn>3</mml:mn>
</mml:msub>
</mml:mrow>
</mml:mfenced>
</mml:mrow>
</mml:mrow>
</mml:math>
</disp-formula>
</p>
<fig id="F3" position="float">
<label>FIGURE 3</label>
<caption>
<p>Authentication key agreement phase.</p>
</caption>
<graphic xlink:href="fphy-13-1522170-g003.tif"/>
</fig>
<p>Then, <inline-formula id="inf93">
<mml:math id="m116">
<mml:mrow>
<mml:msub>
<mml:mi>U</mml:mi>
<mml:mi>i</mml:mi>
</mml:msub>
</mml:mrow>
</mml:math>
</inline-formula> computes the verification message <inline-formula id="inf94">
<mml:math id="m117">
<mml:mrow>
<mml:msubsup>
<mml:mi>V</mml:mi>
<mml:mn>12</mml:mn>
<mml:mo>&#x2a;</mml:mo>
</mml:msubsup>
</mml:mrow>
</mml:math>
</inline-formula> and verifies the correctness of <inline-formula id="inf95">
<mml:math id="m118">
<mml:mrow>
<mml:msubsup>
<mml:mi>V</mml:mi>
<mml:mn>12</mml:mn>
<mml:mo>&#x2a;</mml:mo>
</mml:msubsup>
<mml:mo>&#x3d;</mml:mo>
<mml:msub>
<mml:mi>V</mml:mi>
<mml:mn>12</mml:mn>
</mml:msub>
</mml:mrow>
</mml:math>
</inline-formula>.<disp-formula id="equ22">
<mml:math id="m119">
<mml:mrow>
<mml:msubsup>
<mml:mi>V</mml:mi>
<mml:mn>12</mml:mn>
<mml:mo>&#x2a;</mml:mo>
</mml:msubsup>
<mml:mo>&#x3d;</mml:mo>
<mml:mi>H</mml:mi>
<mml:mrow>
<mml:mfenced open="(" close=")" separators="|">
<mml:mrow>
<mml:mi>P</mml:mi>
<mml:mi>I</mml:mi>
<mml:msub>
<mml:mi>D</mml:mi>
<mml:mi>i</mml:mi>
</mml:msub>
<mml:mo>,</mml:mo>
<mml:msub>
<mml:mi>V</mml:mi>
<mml:mn>10</mml:mn>
</mml:msub>
<mml:mo>,</mml:mo>
<mml:mi>S</mml:mi>
<mml:mi>I</mml:mi>
<mml:msub>
<mml:mi>D</mml:mi>
<mml:mi>j</mml:mi>
</mml:msub>
<mml:mo>,</mml:mo>
<mml:msubsup>
<mml:mi mathvariant="normal">V</mml:mi>
<mml:mn>11</mml:mn>
<mml:mo>&#x2a;</mml:mo>
</mml:msubsup>
<mml:mo>,</mml:mo>
<mml:mi>S</mml:mi>
<mml:msub>
<mml:mi>K</mml:mi>
<mml:mi>i</mml:mi>
</mml:msub>
<mml:mo>,</mml:mo>
<mml:msub>
<mml:mi>T</mml:mi>
<mml:mn>3</mml:mn>
</mml:msub>
</mml:mrow>
</mml:mfenced>
</mml:mrow>
</mml:mrow>
</mml:math>
</disp-formula>
</p>
<p>If the message passes verification, <inline-formula id="inf96">
<mml:math id="m120">
<mml:mrow>
<mml:msub>
<mml:mi>U</mml:mi>
<mml:mi>i</mml:mi>
</mml:msub>
</mml:mrow>
</mml:math>
</inline-formula> can authenticate that the communication requester is <inline-formula id="inf97">
<mml:math id="m121">
<mml:mrow>
<mml:msub>
<mml:mrow>
<mml:mi>S</mml:mi>
<mml:mi>C</mml:mi>
</mml:mrow>
<mml:mi>j</mml:mi>
</mml:msub>
</mml:mrow>
</mml:math>
</inline-formula>, and the session key is also verified. Otherwise, <inline-formula id="inf98">
<mml:math id="m122">
<mml:mrow>
<mml:msub>
<mml:mi>U</mml:mi>
<mml:mi>i</mml:mi>
</mml:msub>
</mml:mrow>
</mml:math>
</inline-formula> rejects the communication request.</p>
</sec>
</sec>
<sec id="s6">
<title>5 Security evaluation</title>
<sec id="s6-1">
<title>5.1 Formal security analysis</title>
<p>Before conducting a formal safety analysis of the proposed protocol, we propose an appropriate safety model [<xref ref-type="bibr" rid="B38">38</xref>, <xref ref-type="bibr" rid="B39">39</xref>]. First, we define three participants in the proposed protocol: U, TRC and SC. In addition, <inline-formula id="inf99">
<mml:math id="m123">
<mml:mrow>
<mml:msubsup>
<mml:mi mathvariant="normal">&#x3a0;</mml:mi>
<mml:mi>U</mml:mi>
<mml:mi>i</mml:mi>
</mml:msubsup>
</mml:mrow>
</mml:math>
</inline-formula>, <inline-formula id="inf100">
<mml:math id="m124">
<mml:mrow>
<mml:msubsup>
<mml:mi mathvariant="normal">&#x3a0;</mml:mi>
<mml:mrow>
<mml:mi>T</mml:mi>
<mml:mi>R</mml:mi>
<mml:mi>C</mml:mi>
</mml:mrow>
<mml:mi>j</mml:mi>
</mml:msubsup>
</mml:mrow>
</mml:math>
</inline-formula> and <inline-formula id="inf101">
<mml:math id="m125">
<mml:mrow>
<mml:msubsup>
<mml:mi mathvariant="normal">&#x3a0;</mml:mi>
<mml:mrow>
<mml:mi>S</mml:mi>
<mml:mi>C</mml:mi>
</mml:mrow>
<mml:mi>k</mml:mi>
</mml:msubsup>
</mml:mrow>
</mml:math>
</inline-formula> respectively represent the instance i, j, and k of U, TRC and SC, which are also called the prophecy machine. Let <inline-formula id="inf102">
<mml:math id="m126">
<mml:mrow>
<mml:mi mathvariant="normal">&#x3a0;</mml:mi>
</mml:mrow>
</mml:math>
</inline-formula> be the set of instances, and <inline-formula id="inf103">
<mml:math id="m127">
<mml:mrow>
<mml:msup>
<mml:mi mathvariant="normal">&#x3a0;</mml:mi>
<mml:mi>s</mml:mi>
</mml:msup>
</mml:mrow>
</mml:math>
</inline-formula> be the s-th instance of &#x3a0;. Define an attacker <inline-formula id="inf104">
<mml:math id="m128">
<mml:mrow>
<mml:mi mathvariant="script">A</mml:mi>
</mml:mrow>
</mml:math>
</inline-formula> can make the following queries:<list list-type="simple">
<list-item>
<p>
<inline-formula id="inf105">
<mml:math id="m129">
<mml:mrow>
<mml:mi>E</mml:mi>
<mml:mi>x</mml:mi>
<mml:mi>e</mml:mi>
<mml:mi>c</mml:mi>
<mml:mi>u</mml:mi>
<mml:mi>t</mml:mi>
<mml:mi>e</mml:mi>
<mml:mrow>
<mml:mfenced open="(" close=")" separators="|">
<mml:mrow>
<mml:msubsup>
<mml:mi mathvariant="normal">&#x3a0;</mml:mi>
<mml:mi>U</mml:mi>
<mml:mi>j</mml:mi>
</mml:msubsup>
<mml:mo>,</mml:mo>
<mml:msubsup>
<mml:mi mathvariant="normal">&#x3a0;</mml:mi>
<mml:mrow>
<mml:mi>T</mml:mi>
<mml:mi>R</mml:mi>
<mml:mi>C</mml:mi>
</mml:mrow>
<mml:mi>i</mml:mi>
</mml:msubsup>
<mml:mo>,</mml:mo>
<mml:msubsup>
<mml:mi mathvariant="normal">&#x3a0;</mml:mi>
<mml:mrow>
<mml:mi>S</mml:mi>
<mml:mi>C</mml:mi>
</mml:mrow>
<mml:mi>k</mml:mi>
</mml:msubsup>
</mml:mrow>
</mml:mfenced>
</mml:mrow>
</mml:mrow>
</mml:math>
</inline-formula>: By executing this query, <inline-formula id="inf106">
<mml:math id="m130">
<mml:mrow>
<mml:mi mathvariant="script">A</mml:mi>
</mml:mrow>
</mml:math>
</inline-formula> can intercept all messages during the communication between U, TRC and SC.</p>
</list-item>
</list>
</p>
<p>
<list list-type="simple">
<list-item>
<p>
<inline-formula id="inf107">
<mml:math id="m131">
<mml:mrow>
<mml:mi>H</mml:mi>
<mml:mi>a</mml:mi>
<mml:mi>s</mml:mi>
<mml:mi>h</mml:mi>
<mml:mrow>
<mml:mfenced open="(" close=")" separators="|">
<mml:mrow>
<mml:mi>m</mml:mi>
</mml:mrow>
</mml:mfenced>
</mml:mrow>
</mml:mrow>
</mml:math>
</inline-formula>: This query simulates the opponent <inline-formula id="inf108">
<mml:math id="m132">
<mml:mrow>
<mml:mi mathvariant="script">A</mml:mi>
</mml:mrow>
</mml:math>
</inline-formula> to receive the hash results by <inline-formula id="inf109">
<mml:math id="m133">
<mml:mrow>
<mml:mi>H</mml:mi>
<mml:mi>a</mml:mi>
<mml:mi>s</mml:mi>
<mml:mi>h</mml:mi>
</mml:mrow>
</mml:math>
</inline-formula> query. After getting this query, if there are <italic>Has</italic>&#x210e; records in the query, the result will be returned, otherwise a random number needs to be selected and returned.</p>
</list-item>
</list>
</p>
<p>
<list list-type="simple">
<list-item>
<p>
<inline-formula id="inf110">
<mml:math id="m134">
<mml:mrow>
<mml:mi>R</mml:mi>
<mml:mi>e</mml:mi>
<mml:mi>v</mml:mi>
<mml:mi>e</mml:mi>
<mml:mi>a</mml:mi>
<mml:mi>l</mml:mi>
<mml:mrow>
<mml:mfenced open="(" close=")" separators="|">
<mml:mrow>
<mml:msup>
<mml:mi mathvariant="normal">&#x3a0;</mml:mi>
<mml:mi>s</mml:mi>
</mml:msup>
</mml:mrow>
</mml:mfenced>
</mml:mrow>
</mml:mrow>
</mml:math>
</inline-formula>: The current session key established between <inline-formula id="inf111">
<mml:math id="m135">
<mml:mrow>
<mml:msup>
<mml:mi mathvariant="normal">&#x3a0;</mml:mi>
<mml:mi>s</mml:mi>
</mml:msup>
</mml:mrow>
</mml:math>
</inline-formula> and its partner is disclosed to <inline-formula id="inf112">
<mml:math id="m136">
<mml:mrow>
<mml:mi mathvariant="script">A</mml:mi>
</mml:mrow>
</mml:math>
</inline-formula> by executing this query.</p>
</list-item>
</list>
</p>
<p>
<list list-type="simple">
<list-item>
<p>
<inline-formula id="inf113">
<mml:math id="m137">
<mml:mrow>
<mml:mi>S</mml:mi>
<mml:mi>e</mml:mi>
<mml:mi>n</mml:mi>
<mml:mi>d</mml:mi>
<mml:mrow>
<mml:mfenced open="(" close=")" separators="|">
<mml:mrow>
<mml:msup>
<mml:mi mathvariant="normal">&#x3a0;</mml:mi>
<mml:mi>s</mml:mi>
</mml:msup>
<mml:mo>,</mml:mo>
<mml:mi>m</mml:mi>
</mml:mrow>
</mml:mfenced>
</mml:mrow>
</mml:mrow>
</mml:math>
</inline-formula> : This query is designed to simulate an active attack initiated by <inline-formula id="inf114">
<mml:math id="m138">
<mml:mrow>
<mml:mi mathvariant="script">A</mml:mi>
</mml:mrow>
</mml:math>
</inline-formula>, where <inline-formula id="inf115">
<mml:math id="m139">
<mml:mrow>
<mml:mi mathvariant="script">A</mml:mi>
</mml:mrow>
</mml:math>
</inline-formula> pretends a legitimate instance and sends a message <italic>m</italic>. If <italic>m</italic> is the correct message, then <inline-formula id="inf116">
<mml:math id="m140">
<mml:mrow>
<mml:mi mathvariant="script">A</mml:mi>
</mml:mrow>
</mml:math>
</inline-formula> can retrieve the corresponding feedback message per protocol <italic>P</italic>. Otherwise, the query will be terminated.</p>
</list-item>
</list>
</p>
<p>
<list list-type="simple">
<list-item>
<p>
<inline-formula id="inf117">
<mml:math id="m141">
<mml:mrow>
<mml:mi>T</mml:mi>
<mml:mi>e</mml:mi>
<mml:mi>s</mml:mi>
<mml:mi>t</mml:mi>
<mml:mrow>
<mml:mfenced open="(" close=")" separators="|">
<mml:mrow>
<mml:msup>
<mml:mi mathvariant="normal">&#x3a0;</mml:mi>
<mml:mi>s</mml:mi>
</mml:msup>
</mml:mrow>
</mml:mfenced>
</mml:mrow>
</mml:mrow>
</mml:math>
</inline-formula>: The query assesses the semantic security of the authenticated key. During the execution of protocol, <inline-formula id="inf118">
<mml:math id="m142">
<mml:mrow>
<mml:mi mathvariant="script">A</mml:mi>
</mml:mrow>
</mml:math>
</inline-formula> may initiate a test query to challenge the security of the key. Upon receiving this query, <inline-formula id="inf119">
<mml:math id="m143">
<mml:mrow>
<mml:msup>
<mml:mi mathvariant="normal">&#x3a0;</mml:mi>
<mml:mi>j</mml:mi>
</mml:msup>
</mml:mrow>
</mml:math>
</inline-formula> returns a genuine authentication key or a randomly generated string based on an unbiased coin flip.</p>
</list-item>
</list>
</p>
<sec id="s6-1-1">
<title>5.1.1 Session key security</title>
<p>It defines allowing an attacker <inline-formula id="inf120">
<mml:math id="m144">
<mml:mrow>
<mml:mi mathvariant="script">A</mml:mi>
</mml:mrow>
</mml:math>
</inline-formula> to interrogate many <italic>Test</italic> queries. If <italic>Test</italic> query targets an instance of a dishonest participant paired with an honest participant or an instance of a dishonest participant whose intended partner is also dishonest, the system will return the genuine authenticated key. Otherwise, it utilizes an unbiased coin flip to decide whether to return the actual key K or a randomly generated key. <inline-formula id="inf121">
<mml:math id="m145">
<mml:mrow>
<mml:mi mathvariant="script">A</mml:mi>
</mml:mrow>
</mml:math>
</inline-formula> tries to use the <italic>Test</italic> query to correctly guess <inline-formula id="inf122">
<mml:math id="m146">
<mml:mrow>
<mml:mi>c</mml:mi>
<mml:mo>&#x2208;</mml:mo>
<mml:mrow>
<mml:mfenced open="{" close="}" separators="|">
<mml:mrow>
<mml:mn>0</mml:mn>
<mml:mo>,</mml:mo>
<mml:mn>1</mml:mn>
</mml:mrow>
</mml:mfenced>
</mml:mrow>
</mml:mrow>
</mml:math>
</inline-formula>. If <inline-formula id="inf123">
<mml:math id="m147">
<mml:mrow>
<mml:mi mathvariant="script">A</mml:mi>
</mml:mrow>
</mml:math>
</inline-formula> successfully guessed the bit <inline-formula id="inf124">
<mml:math id="m148">
<mml:mrow>
<mml:mi>c</mml:mi>
</mml:mrow>
</mml:math>
</inline-formula>, where <inline-formula id="inf125">
<mml:math id="m149">
<mml:mrow>
<mml:mi mathvariant="script">A</mml:mi>
</mml:mrow>
</mml:math>
</inline-formula> is able to successfully distinguish the true K from a randomly generated string, <inline-formula id="inf126">
<mml:math id="m150">
<mml:mrow>
<mml:mi mathvariant="script">A</mml:mi>
</mml:mrow>
</mml:math>
</inline-formula> wins. <inline-formula id="inf127">
<mml:math id="m151">
<mml:mrow>
<mml:msubsup>
<mml:mrow>
<mml:mi>A</mml:mi>
<mml:mi>d</mml:mi>
<mml:mi>v</mml:mi>
</mml:mrow>
<mml:mi>P</mml:mi>
<mml:mrow>
<mml:mi>S</mml:mi>
<mml:mi>K</mml:mi>
</mml:mrow>
</mml:msubsup>
<mml:mrow>
<mml:mfenced open="(" close=")" separators="|">
<mml:mrow>
<mml:mi mathvariant="script">A</mml:mi>
</mml:mrow>
</mml:mfenced>
</mml:mrow>
</mml:mrow>
</mml:math>
</inline-formula> is defined as the advantage of the event where the opponent <inline-formula id="inf128">
<mml:math id="m152">
<mml:mrow>
<mml:mi mathvariant="script">A</mml:mi>
</mml:mrow>
</mml:math>
</inline-formula> wins the game for protocol <italic>P</italic>, and if the <inline-formula id="inf129">
<mml:math id="m153">
<mml:mrow>
<mml:msubsup>
<mml:mrow>
<mml:mi>A</mml:mi>
<mml:mi>d</mml:mi>
<mml:mi>v</mml:mi>
</mml:mrow>
<mml:mi>P</mml:mi>
<mml:mrow>
<mml:mi>S</mml:mi>
<mml:mi>K</mml:mi>
</mml:mrow>
</mml:msubsup>
<mml:mrow>
<mml:mfenced open="(" close=")" separators="|">
<mml:mrow>
<mml:mi mathvariant="script">A</mml:mi>
</mml:mrow>
</mml:mfenced>
</mml:mrow>
</mml:mrow>
</mml:math>
</inline-formula> is negligible, protocol <italic>P</italic> is safe.</p>
<p>
<statement content-type="theorem" id="Theorem_1">
<label>Theorem 1</label>
<p>Suppose <inline-formula id="inf130">
<mml:math id="m154">
<mml:mrow>
<mml:mi mathvariant="script">A</mml:mi>
</mml:mrow>
</mml:math>
</inline-formula> represents the attackers, <italic>P</italic>, <inline-formula id="inf131">
<mml:math id="m155">
<mml:mrow>
<mml:msub>
<mml:mi>q</mml:mi>
<mml:mi>s</mml:mi>
</mml:msub>
</mml:mrow>
</mml:math>
</inline-formula>, <inline-formula id="inf132">
<mml:math id="m156">
<mml:mrow>
<mml:msub>
<mml:mi>q</mml:mi>
<mml:mi>h</mml:mi>
</mml:msub>
</mml:mrow>
</mml:math>
</inline-formula>, <inline-formula id="inf133">
<mml:math id="m157">
<mml:mrow>
<mml:mfenced open="|" close="|" separators="|">
<mml:mrow>
<mml:mi>H</mml:mi>
<mml:mi>A</mml:mi>
<mml:mi>S</mml:mi>
<mml:mi>H</mml:mi>
</mml:mrow>
</mml:mfenced>
</mml:mrow>
</mml:math>
</inline-formula> and <inline-formula id="inf134">
<mml:math id="m158">
<mml:mrow>
<mml:msubsup>
<mml:mrow>
<mml:mi>A</mml:mi>
<mml:mi>d</mml:mi>
<mml:mi>v</mml:mi>
</mml:mrow>
<mml:mi mathvariant="script">A</mml:mi>
<mml:mtext>CMBDHP</mml:mtext>
</mml:msubsup>
<mml:mrow>
<mml:mfenced open="(" close=")" separators="|">
<mml:mrow>
<mml:mi>t</mml:mi>
</mml:mrow>
</mml:mfenced>
</mml:mrow>
</mml:mrow>
</mml:math>
</inline-formula> represent the proposed protocol, the number of <inline-formula id="inf135">
<mml:math id="m159">
<mml:mrow>
<mml:mi>S</mml:mi>
<mml:mi>e</mml:mi>
<mml:mi>n</mml:mi>
<mml:mi>d</mml:mi>
</mml:mrow>
</mml:math>
</inline-formula> queries, the number of <inline-formula id="inf136">
<mml:math id="m160">
<mml:mrow>
<mml:mi>H</mml:mi>
<mml:mi>a</mml:mi>
<mml:mi>s</mml:mi>
<mml:mi>h</mml:mi>
</mml:mrow>
</mml:math>
</inline-formula> queries, the range space of <inline-formula id="inf137">
<mml:math id="m161">
<mml:mrow>
<mml:mi>H</mml:mi>
<mml:mrow>
<mml:mfenced open="(" close=")" separators="|">
<mml:mrow/>
</mml:mfenced>
</mml:mrow>
</mml:mrow>
</mml:math>
</inline-formula> and the advantage of <inline-formula id="inf138">
<mml:math id="m162">
<mml:mrow>
<mml:mi mathvariant="script">A</mml:mi>
</mml:mrow>
</mml:math>
</inline-formula> cracking CMBDHP in time <inline-formula id="inf139">
<mml:math id="m163">
<mml:mrow>
<mml:mi>t</mml:mi>
</mml:mrow>
</mml:math>
</inline-formula>. The advantage of <inline-formula id="inf140">
<mml:math id="m164">
<mml:mrow>
<mml:mi mathvariant="script">A</mml:mi>
</mml:mrow>
</mml:math>
</inline-formula> in breaking the group session key security of the protocol can be estimated as <xref ref-type="disp-formula" rid="e3">Formula 3</xref>:<disp-formula id="e3">
<mml:math id="m165">
<mml:mrow>
<mml:msubsup>
<mml:mrow>
<mml:mi>A</mml:mi>
<mml:mi>d</mml:mi>
<mml:mi>v</mml:mi>
</mml:mrow>
<mml:mi>P</mml:mi>
<mml:mrow>
<mml:mi>S</mml:mi>
<mml:mi>K</mml:mi>
</mml:mrow>
</mml:msubsup>
<mml:mrow>
<mml:mfenced open="(" close=")" separators="|">
<mml:mrow>
<mml:mi mathvariant="script">A</mml:mi>
</mml:mrow>
</mml:mfenced>
</mml:mrow>
<mml:mo>&#x2264;</mml:mo>
<mml:mfrac>
<mml:msubsup>
<mml:mi>q</mml:mi>
<mml:mi>h</mml:mi>
<mml:mn>2</mml:mn>
</mml:msubsup>
<mml:mrow>
<mml:mfenced open="|" close="|" separators="|">
<mml:mrow>
<mml:mi>H</mml:mi>
<mml:mi>A</mml:mi>
<mml:mi>S</mml:mi>
<mml:mi>H</mml:mi>
</mml:mrow>
</mml:mfenced>
</mml:mrow>
</mml:mfrac>
<mml:mo>&#x2b;</mml:mo>
<mml:msubsup>
<mml:mrow>
<mml:mn>2</mml:mn>
<mml:mi>A</mml:mi>
<mml:mi>d</mml:mi>
<mml:mi>v</mml:mi>
</mml:mrow>
<mml:mi mathvariant="script">A</mml:mi>
<mml:mtext>CMBDHP</mml:mtext>
</mml:msubsup>
<mml:mrow>
<mml:mfenced open="(" close=")" separators="|">
<mml:mrow>
<mml:mi>t</mml:mi>
</mml:mrow>
</mml:mfenced>
</mml:mrow>
</mml:mrow>
</mml:math>
<label>(3)</label>
</disp-formula>
</p>
<p>Prove: we proved it by playing four games, <inline-formula id="inf141">
<mml:math id="m166">
<mml:mrow>
<mml:msub>
<mml:mrow>
<mml:mi>G</mml:mi>
<mml:mi>m</mml:mi>
</mml:mrow>
<mml:mi>i</mml:mi>
</mml:msub>
</mml:mrow>
</mml:math>
</inline-formula> (i &#x3d; 0,1,2,3). Let <inline-formula id="inf142">
<mml:math id="m167">
<mml:mrow>
<mml:msub>
<mml:mrow>
<mml:mi>S</mml:mi>
<mml:mi>u</mml:mi>
<mml:mi>c</mml:mi>
<mml:mi>c</mml:mi>
</mml:mrow>
<mml:msub>
<mml:mrow>
<mml:mi>G</mml:mi>
<mml:mi>m</mml:mi>
</mml:mrow>
<mml:mi>i</mml:mi>
</mml:msub>
</mml:msub>
</mml:mrow>
</mml:math>
</inline-formula> denote the success probability of <inline-formula id="inf143"> <mml:math id="m168"> <mml:mrow> <mml:mi mathvariant="script">A</mml:mi> </mml:mrow> </mml:math> </inline-formula> winning the <inline-formula id="inf144">
<mml:math id="m169">
<mml:mrow>
<mml:msub>
<mml:mrow>
<mml:mi>G</mml:mi>
<mml:mi>m</mml:mi>
</mml:mrow>
<mml:mi>i</mml:mi>
</mml:msub>
</mml:mrow>
</mml:math>
</inline-formula> while guessing the correct bit <italic>c</italic>, and the response advantage probability of <inline-formula id="inf145">
<mml:math id="m170">
<mml:mrow>
<mml:mi mathvariant="script">A</mml:mi>
</mml:mrow>
</mml:math>
</inline-formula> is defined as <inline-formula id="inf146">
<mml:math id="m171">
<mml:mrow>
<mml:msub>
<mml:mrow>
<mml:mi>A</mml:mi>
<mml:mi>d</mml:mi>
<mml:mi>v</mml:mi>
</mml:mrow>
<mml:msub>
<mml:mrow>
<mml:mi>G</mml:mi>
<mml:mi>m</mml:mi>
</mml:mrow>
<mml:mi>i</mml:mi>
</mml:msub>
</mml:msub>
<mml:mo>&#x3d;</mml:mo>
<mml:mi>Pr</mml:mi>
<mml:mtext>&#x2009;</mml:mtext>
<mml:mrow>
<mml:mfenced open="[" close="]" separators="|">
<mml:mrow>
<mml:msub>
<mml:mrow>
<mml:mi>S</mml:mi>
<mml:mi>u</mml:mi>
<mml:mi>c</mml:mi>
<mml:mi>c</mml:mi>
</mml:mrow>
<mml:msub>
<mml:mrow>
<mml:mi>G</mml:mi>
<mml:mi>m</mml:mi>
</mml:mrow>
<mml:mi>i</mml:mi>
</mml:msub>
</mml:msub>
</mml:mrow>
</mml:mfenced>
</mml:mrow>
</mml:mrow>
</mml:math>
</inline-formula>. Below is a detailed analysis for each <inline-formula id="inf147">
<mml:math id="m172">
<mml:mrow>
<mml:msub>
<mml:mrow>
<mml:mi>G</mml:mi>
<mml:mi>m</mml:mi>
</mml:mrow>
<mml:mi>i</mml:mi>
</mml:msub>
</mml:mrow>
</mml:math>
</inline-formula>.</p>
<p>
<inline-formula id="inf148">
<mml:math id="m173">
<mml:mrow>
<mml:msub>
<mml:mrow>
<mml:mi>G</mml:mi>
<mml:mi>m</mml:mi>
</mml:mrow>
<mml:mn>0</mml:mn>
</mml:msub>
</mml:mrow>
</mml:math>
</inline-formula>: <inline-formula id="inf149">
<mml:math id="m174">
<mml:mrow>
<mml:msub>
<mml:mrow>
<mml:mi>G</mml:mi>
<mml:mi>m</mml:mi>
</mml:mrow>
<mml:mn>0</mml:mn>
</mml:msub>
</mml:mrow>
</mml:math>
</inline-formula> is a real attack of <inline-formula id="inf150">
<mml:math id="m175">
<mml:mrow>
<mml:mi mathvariant="script">A</mml:mi>
</mml:mrow>
</mml:math>
</inline-formula>. And from the semantic security definition of the proposed protocol, <xref ref-type="disp-formula" rid="e4">Formula 4</xref> can be obtained that:<disp-formula id="e4">
<mml:math id="m176">
<mml:mrow>
<mml:msubsup>
<mml:mrow>
<mml:mi>A</mml:mi>
<mml:mi>d</mml:mi>
<mml:mi>v</mml:mi>
</mml:mrow>
<mml:mi>P</mml:mi>
<mml:mrow>
<mml:mi>S</mml:mi>
<mml:mi>K</mml:mi>
</mml:mrow>
</mml:msubsup>
<mml:mrow>
<mml:mfenced open="(" close=")" separators="|">
<mml:mrow>
<mml:mi mathvariant="script">A</mml:mi>
</mml:mrow>
</mml:mfenced>
</mml:mrow>
<mml:mo>&#x3d;</mml:mo>
<mml:mo>&#x7c;</mml:mo>
<mml:mn>2</mml:mn>
<mml:mo>&#x2061;</mml:mo>
<mml:mi>Pr</mml:mi>
<mml:mrow>
<mml:mfenced open="[" close="]" separators="|">
<mml:mrow>
<mml:msub>
<mml:mrow>
<mml:mi>A</mml:mi>
<mml:mi>d</mml:mi>
<mml:mi>v</mml:mi>
</mml:mrow>
<mml:msub>
<mml:mrow>
<mml:mi>G</mml:mi>
<mml:mi>m</mml:mi>
</mml:mrow>
<mml:mn>0</mml:mn>
</mml:msub>
</mml:msub>
</mml:mrow>
</mml:mfenced>
</mml:mrow>
<mml:mrow>
<mml:mfenced open="" close="|" separators="|">
<mml:mrow>
<mml:mrow>
<mml:mo>&#x2212;</mml:mo>
<mml:mn>1</mml:mn>
</mml:mrow>
</mml:mrow>
</mml:mfenced>
</mml:mrow>
</mml:mrow>
</mml:math>
<label>(4)</label>
</disp-formula>
</p>
<p>
<inline-formula id="inf151">
<mml:math id="m177">
<mml:mrow>
<mml:msub>
<mml:mrow>
<mml:mi>G</mml:mi>
<mml:mi>m</mml:mi>
</mml:mrow>
<mml:mn>1</mml:mn>
</mml:msub>
</mml:mrow>
</mml:math>
</inline-formula>: <inline-formula id="inf152">
<mml:math id="m178">
<mml:mrow>
<mml:msub>
<mml:mrow>
<mml:mi>G</mml:mi>
<mml:mi>m</mml:mi>
</mml:mrow>
<mml:mn>1</mml:mn>
</mml:msub>
</mml:mrow>
</mml:math>
</inline-formula> is a simulated eavesdropping attack. Under this game, <inline-formula id="inf153">
<mml:math id="m179">
<mml:mrow>
<mml:mi mathvariant="script">A</mml:mi>
</mml:mrow>
</mml:math>
</inline-formula> intercepts all the authentication information <inline-formula id="inf154">
<mml:math id="m180">
<mml:mrow>
<mml:mrow>
<mml:mfenced open="{" close="}" separators="|">
<mml:mrow>
<mml:msub>
<mml:mi>V</mml:mi>
<mml:mn>1</mml:mn>
</mml:msub>
<mml:mo>,</mml:mo>
<mml:msub>
<mml:mi>V</mml:mi>
<mml:mn>3</mml:mn>
</mml:msub>
<mml:mo>,</mml:mo>
<mml:msub>
<mml:mi>V</mml:mi>
<mml:mn>4</mml:mn>
</mml:msub>
<mml:mo>,</mml:mo>
<mml:msub>
<mml:mi>V</mml:mi>
<mml:mn>5</mml:mn>
</mml:msub>
<mml:mo>,</mml:mo>
<mml:msub>
<mml:mi>V</mml:mi>
<mml:mn>6</mml:mn>
</mml:msub>
<mml:mo>,</mml:mo>
<mml:msub>
<mml:mi>T</mml:mi>
<mml:mn>1</mml:mn>
</mml:msub>
</mml:mrow>
</mml:mfenced>
</mml:mrow>
<mml:mo>,</mml:mo>
<mml:mrow>
<mml:mfenced open="{" close="}" separators="|">
<mml:mrow>
<mml:msub>
<mml:mrow>
<mml:msubsup>
<mml:mrow>
<mml:mi>S</mml:mi>
<mml:mi>I</mml:mi>
<mml:mi>D</mml:mi>
</mml:mrow>
<mml:mi>j</mml:mi>
<mml:mo>&#x2a;</mml:mo>
</mml:msubsup>
<mml:mo>,</mml:mo>
<mml:mi>V</mml:mi>
</mml:mrow>
<mml:mn>1</mml:mn>
</mml:msub>
<mml:mo>,</mml:mo>
<mml:msub>
<mml:mi>V</mml:mi>
<mml:mn>7</mml:mn>
</mml:msub>
<mml:mo>,</mml:mo>
<mml:msub>
<mml:mi>V</mml:mi>
<mml:mn>8</mml:mn>
</mml:msub>
<mml:mo>,</mml:mo>
<mml:msub>
<mml:mi>V</mml:mi>
<mml:mn>9</mml:mn>
</mml:msub>
<mml:mo>,</mml:mo>
<mml:msub>
<mml:mi>T</mml:mi>
<mml:mn>1</mml:mn>
</mml:msub>
</mml:mrow>
</mml:mfenced>
</mml:mrow>
<mml:mo>,</mml:mo>
<mml:mrow>
<mml:mfenced open="{" close="}" separators="|">
<mml:mrow>
<mml:msub>
<mml:mi>V</mml:mi>
<mml:mn>10</mml:mn>
</mml:msub>
<mml:mo>,</mml:mo>
<mml:msub>
<mml:mi>V</mml:mi>
<mml:mn>12</mml:mn>
</mml:msub>
<mml:mo>,</mml:mo>
<mml:msub>
<mml:mi>T</mml:mi>
<mml:mn>3</mml:mn>
</mml:msub>
</mml:mrow>
</mml:mfenced>
</mml:mrow>
</mml:mrow>
</mml:math>
</inline-formula> and simulates through the <inline-formula id="inf155">
<mml:math id="m181">
<mml:mrow>
<mml:mi>E</mml:mi>
<mml:mi>x</mml:mi>
<mml:mi>e</mml:mi>
<mml:mi>c</mml:mi>
<mml:mi>u</mml:mi>
<mml:mi>t</mml:mi>
<mml:mi>e</mml:mi>
</mml:mrow>
</mml:math>
</inline-formula> query. Then <inline-formula id="inf156">
<mml:math id="m182">
<mml:mrow>
<mml:mi mathvariant="script">A</mml:mi>
</mml:mrow>
</mml:math>
</inline-formula> performs the <inline-formula id="inf157">
<mml:math id="m183">
<mml:mrow>
<mml:mi>T</mml:mi>
<mml:mi>e</mml:mi>
<mml:mi>s</mml:mi>
<mml:mi>t</mml:mi>
</mml:mrow>
</mml:math>
</inline-formula> query to check whether its output gives the true group session key or a random value. Since the intercepted messages do not endanger the temporary/long-term secrets of any of the communication entities, the <inline-formula id="inf158">
<mml:math id="m184">
<mml:mrow>
<mml:msub>
<mml:mrow>
<mml:mi>G</mml:mi>
<mml:mi>m</mml:mi>
</mml:mrow>
<mml:mn>1</mml:mn>
</mml:msub>
</mml:mrow>
</mml:math>
</inline-formula> winning chances do not increase. Therefore, <xref ref-type="disp-formula" rid="e5">Formula 5</xref> can be obtained that:<disp-formula id="e5">
<mml:math id="m185">
<mml:mrow>
<mml:mi>Pr</mml:mi>
<mml:mrow>
<mml:mfenced open="[" close="]" separators="|">
<mml:mrow>
<mml:msub>
<mml:mrow>
<mml:mi>A</mml:mi>
<mml:mi>d</mml:mi>
<mml:mi>v</mml:mi>
</mml:mrow>
<mml:msub>
<mml:mrow>
<mml:mi>G</mml:mi>
<mml:mi>m</mml:mi>
</mml:mrow>
<mml:mn>1</mml:mn>
</mml:msub>
</mml:msub>
</mml:mrow>
</mml:mfenced>
</mml:mrow>
<mml:mo>&#x3d;</mml:mo>
<mml:mi>Pr</mml:mi>
<mml:mrow>
<mml:mfenced open="[" close="]" separators="|">
<mml:mrow>
<mml:msub>
<mml:mrow>
<mml:mi>A</mml:mi>
<mml:mi>d</mml:mi>
<mml:mi>v</mml:mi>
</mml:mrow>
<mml:msub>
<mml:mrow>
<mml:mi>G</mml:mi>
<mml:mi>m</mml:mi>
</mml:mrow>
<mml:mn>0</mml:mn>
</mml:msub>
</mml:msub>
</mml:mrow>
</mml:mfenced>
</mml:mrow>
</mml:mrow>
</mml:math>
<label>(5)</label>
</disp-formula>
</p>
<p>
<inline-formula id="inf159">
<mml:math id="m186">
<mml:mrow>
<mml:msub>
<mml:mrow>
<mml:mi>G</mml:mi>
<mml:mi>m</mml:mi>
</mml:mrow>
<mml:mn>2</mml:mn>
</mml:msub>
</mml:mrow>
</mml:math>
</inline-formula>: The difference from the previous game <inline-formula id="inf160">
<mml:math id="m187">
<mml:mrow>
<mml:msub>
<mml:mrow>
<mml:mi>G</mml:mi>
<mml:mi>m</mml:mi>
</mml:mrow>
<mml:mn>1</mml:mn>
</mml:msub>
</mml:mrow>
</mml:math>
</inline-formula> is that <inline-formula id="inf161">
<mml:math id="m188">
<mml:mrow>
<mml:msub>
<mml:mrow>
<mml:mi>G</mml:mi>
<mml:mi>m</mml:mi>
</mml:mrow>
<mml:mn>2</mml:mn>
</mml:msub>
</mml:mrow>
</mml:math>
</inline-formula> contains <italic>Send</italic> and <italic>Has</italic>&#x210e; queries. <inline-formula id="inf162">
<mml:math id="m189">
<mml:mrow>
<mml:msub>
<mml:mrow>
<mml:mi>G</mml:mi>
<mml:mi>m</mml:mi>
</mml:mrow>
<mml:mn>2</mml:mn>
</mml:msub>
</mml:mrow>
</mml:math>
</inline-formula> simulates an active attack, in which <inline-formula id="inf163">
<mml:math id="m190">
<mml:mrow>
<mml:mi mathvariant="script">A</mml:mi>
</mml:mrow>
</mml:math>
</inline-formula> tries to persuade the communication entity to accept the forged message. While <inline-formula id="inf164">
<mml:math id="m191">
<mml:mrow>
<mml:mi mathvariant="script">A</mml:mi>
</mml:mrow>
</mml:math>
</inline-formula> can repeat <inline-formula id="inf165">
<mml:math id="m192">
<mml:mrow>
<mml:mi>H</mml:mi>
<mml:mi>a</mml:mi>
<mml:mi>s</mml:mi>
<mml:mi>h</mml:mi>
</mml:mrow>
</mml:math>
</inline-formula> queries to check conflicts in authentication messages, each message set is associated with a random number, current timestamp, identity, and secret value. Therefore, <inline-formula id="inf166">
<mml:math id="m193">
<mml:mrow>
<mml:mi mathvariant="script">A</mml:mi>
</mml:mrow>
</mml:math>
</inline-formula> has little chance of collision when making <inline-formula id="inf167">
<mml:math id="m194">
<mml:mrow>
<mml:mi>S</mml:mi>
<mml:mi>e</mml:mi>
<mml:mi>n</mml:mi>
<mml:mi>d</mml:mi>
</mml:mrow>
</mml:math>
</inline-formula> queries. Therefore, according to the birthday paradox, we have <xref ref-type="disp-formula" rid="e6">Formula 6</xref>:<disp-formula id="e6">
<mml:math id="m195">
<mml:mrow>
<mml:mfenced open="|" close="" separators="|">
<mml:mrow>
<mml:mrow>
<mml:mi>Pr</mml:mi>
<mml:mrow>
<mml:mfenced open="[" close="]" separators="|">
<mml:mrow>
<mml:msub>
<mml:mrow>
<mml:mi>A</mml:mi>
<mml:mi>d</mml:mi>
<mml:mi>v</mml:mi>
</mml:mrow>
<mml:msub>
<mml:mrow>
<mml:mi>G</mml:mi>
<mml:mi>m</mml:mi>
</mml:mrow>
<mml:mn>2</mml:mn>
</mml:msub>
</mml:msub>
</mml:mrow>
</mml:mfenced>
</mml:mrow>
<mml:mo>&#x2212;</mml:mo>
<mml:mi>Pr</mml:mi>
<mml:mrow>
<mml:mfenced open="[" close="]" separators="|">
<mml:mrow>
<mml:msub>
<mml:mrow>
<mml:mi>A</mml:mi>
<mml:mi>d</mml:mi>
<mml:mi>v</mml:mi>
</mml:mrow>
<mml:msub>
<mml:mrow>
<mml:mi>G</mml:mi>
<mml:mi>m</mml:mi>
</mml:mrow>
<mml:mn>1</mml:mn>
</mml:msub>
</mml:msub>
</mml:mrow>
</mml:mfenced>
</mml:mrow>
<mml:mrow>
<mml:mfenced open="|" close="" separators="|">
<mml:mrow>
<mml:mo>&#x2264;</mml:mo>
</mml:mrow>
</mml:mfenced>
</mml:mrow>
<mml:mfrac>
<mml:msubsup>
<mml:mi>q</mml:mi>
<mml:mi>h</mml:mi>
<mml:mn>2</mml:mn>
</mml:msubsup>
<mml:mrow>
<mml:mfenced open="" close="|" separators="|">
<mml:mrow>
<mml:mrow>
<mml:mrow>
<mml:mfenced open="" close="|" separators="|">
<mml:mrow>
<mml:mn>2</mml:mn>
</mml:mrow>
</mml:mfenced>
</mml:mrow>
<mml:mi>H</mml:mi>
<mml:mi>A</mml:mi>
<mml:mi>S</mml:mi>
<mml:mi>H</mml:mi>
</mml:mrow>
</mml:mrow>
</mml:mfenced>
</mml:mrow>
</mml:mfrac>
</mml:mrow>
</mml:mrow>
</mml:mfenced>
</mml:mrow>
</mml:math>
<label>(6)</label>
</disp-formula>
</p>
<p>
<inline-formula id="inf168">
<mml:math id="m196">
<mml:mrow>
<mml:msub>
<mml:mrow>
<mml:mi>G</mml:mi>
<mml:mi>m</mml:mi>
</mml:mrow>
<mml:mn>3</mml:mn>
</mml:msub>
</mml:mrow>
</mml:math>
</inline-formula>: In this final game, <inline-formula id="inf169">
<mml:math id="m197">
<mml:mrow>
<mml:mi mathvariant="script">A</mml:mi>
</mml:mrow>
</mml:math>
</inline-formula> tries to use the intercepted messages to calculate the session keys and to solve the <inline-formula id="inf170">
<mml:math id="m198">
<mml:mtext>CMBDHP</mml:mtext>
</mml:math>
</inline-formula> problem. If <inline-formula id="inf171">
<mml:math id="m199">
<mml:mrow>
<mml:mi mathvariant="script">A</mml:mi>
</mml:mrow>
</mml:math>
</inline-formula> tries to calculate the key <inline-formula id="inf172">
<mml:math id="m200">
<mml:mrow>
<mml:mi>S</mml:mi>
<mml:msub>
<mml:mi>K</mml:mi>
<mml:mi>i</mml:mi>
</mml:msub>
<mml:mo>&#x3d;</mml:mo>
<mml:mi>H</mml:mi>
<mml:mrow>
<mml:mfenced open="(" close=")" separators="|">
<mml:mrow>
<mml:mi>P</mml:mi>
<mml:mi>I</mml:mi>
<mml:msub>
<mml:mi>D</mml:mi>
<mml:mi>i</mml:mi>
</mml:msub>
<mml:mo>,</mml:mo>
<mml:mi>S</mml:mi>
<mml:mi>I</mml:mi>
<mml:msub>
<mml:mi>D</mml:mi>
<mml:mi>j</mml:mi>
</mml:msub>
<mml:mo>,</mml:mo>
<mml:msubsup>
<mml:mi mathvariant="normal">V</mml:mi>
<mml:mn>11</mml:mn>
<mml:mo>&#x2a;</mml:mo>
</mml:msubsup>
<mml:mo>,</mml:mo>
<mml:msub>
<mml:mi>T</mml:mi>
<mml:mn>3</mml:mn>
</mml:msub>
</mml:mrow>
</mml:mfenced>
</mml:mrow>
</mml:mrow>
</mml:math>
</inline-formula>, the secret value <inline-formula id="inf173">
<mml:math id="m201">
<mml:mrow>
<mml:msubsup>
<mml:mi mathvariant="normal">V</mml:mi>
<mml:mn>11</mml:mn>
<mml:mo>&#x2a;</mml:mo>
</mml:msubsup>
</mml:mrow>
</mml:math>
</inline-formula> need to be known. This means that <inline-formula id="inf174">
<mml:math id="m202">
<mml:mrow>
<mml:mi mathvariant="script">A</mml:mi>
</mml:mrow>
</mml:math>
</inline-formula> needs to solve the <inline-formula id="inf175">
<mml:math id="m203">
<mml:mtext>CMBDHP</mml:mtext>
</mml:math>
</inline-formula> in the shortest time to obtain the session key. Therefore, <xref ref-type="disp-formula" rid="e7">Formula 7</xref> can be obtained that:<disp-formula id="e7">
<mml:math id="m204">
<mml:mrow>
<mml:mfenced open="|" close="" separators="|">
<mml:mrow>
<mml:mrow>
<mml:mi>Pr</mml:mi>
<mml:mrow>
<mml:mfenced open="[" close="]" separators="|">
<mml:mrow>
<mml:msub>
<mml:mrow>
<mml:mi>A</mml:mi>
<mml:mi>d</mml:mi>
<mml:mi>v</mml:mi>
</mml:mrow>
<mml:msub>
<mml:mrow>
<mml:mi>G</mml:mi>
<mml:mi>m</mml:mi>
</mml:mrow>
<mml:mn>3</mml:mn>
</mml:msub>
</mml:msub>
</mml:mrow>
</mml:mfenced>
</mml:mrow>
<mml:mo>&#x2212;</mml:mo>
<mml:mi>Pr</mml:mi>
<mml:mrow>
<mml:mfenced open="[" close="]" separators="|">
<mml:mrow>
<mml:msub>
<mml:mrow>
<mml:mi>A</mml:mi>
<mml:mi>d</mml:mi>
<mml:mi>v</mml:mi>
</mml:mrow>
<mml:msub>
<mml:mrow>
<mml:mi>G</mml:mi>
<mml:mi>m</mml:mi>
</mml:mrow>
<mml:mn>2</mml:mn>
</mml:msub>
</mml:msub>
</mml:mrow>
</mml:mfenced>
</mml:mrow>
<mml:mrow>
<mml:mfenced open="|" close="" separators="|">
<mml:mrow>
<mml:mo>&#x2264;</mml:mo>
</mml:mrow>
</mml:mfenced>
</mml:mrow>
<mml:msubsup>
<mml:mrow>
<mml:mi>A</mml:mi>
<mml:mi>d</mml:mi>
<mml:mi>v</mml:mi>
</mml:mrow>
<mml:mi mathvariant="script">A</mml:mi>
<mml:mrow>
<mml:mi>E</mml:mi>
<mml:mi>C</mml:mi>
<mml:mi>D</mml:mi>
<mml:mi>H</mml:mi>
<mml:mi>P</mml:mi>
</mml:mrow>
</mml:msubsup>
<mml:mrow>
<mml:mfenced open="(" close=")" separators="|">
<mml:mrow>
<mml:mi>t</mml:mi>
</mml:mrow>
</mml:mfenced>
</mml:mrow>
</mml:mrow>
</mml:mrow>
</mml:mfenced>
</mml:mrow>
</mml:math>
<label>(7)</label>
</disp-formula>
</p>
<p>Once all the queries are made by <inline-formula id="inf176">
<mml:math id="m205">
<mml:mrow>
<mml:mi mathvariant="script">A</mml:mi>
</mml:mrow>
</mml:math>
</inline-formula>, the only guess bit <inline-formula id="inf177">
<mml:math id="m206">
<mml:mrow>
<mml:mi>c</mml:mi>
</mml:mrow>
</mml:math>
</inline-formula> is left to win the game and we have <xref ref-type="disp-formula" rid="e8">Formula 8</xref>.<disp-formula id="e8">
<mml:math id="m207">
<mml:mrow>
<mml:mi>Pr</mml:mi>
<mml:mrow>
<mml:mfenced open="[" close="]" separators="|">
<mml:mrow>
<mml:msub>
<mml:mrow>
<mml:mi>A</mml:mi>
<mml:mi>d</mml:mi>
<mml:mi>v</mml:mi>
</mml:mrow>
<mml:msub>
<mml:mrow>
<mml:mi>G</mml:mi>
<mml:mi>m</mml:mi>
</mml:mrow>
<mml:mn>3</mml:mn>
</mml:msub>
</mml:msub>
</mml:mrow>
</mml:mfenced>
</mml:mrow>
<mml:mo>&#x3d;</mml:mo>
<mml:mfrac>
<mml:mrow>
<mml:mn>1</mml:mn>
</mml:mrow>
<mml:mrow>
<mml:mn>2</mml:mn>
</mml:mrow>
</mml:mfrac>
</mml:mrow>
</mml:math>
<label>(8)</label>
</disp-formula>
</p>
<p>According to the formulas, we can get <xref ref-type="disp-formula" rid="e9">Formula 9</xref>:<disp-formula id="e9">
<mml:math id="m208">
<mml:mrow>
<mml:msubsup>
<mml:mrow>
<mml:mi>A</mml:mi>
<mml:mi>d</mml:mi>
<mml:mi>v</mml:mi>
</mml:mrow>
<mml:mi>P</mml:mi>
<mml:mrow>
<mml:mi>S</mml:mi>
<mml:mi>K</mml:mi>
</mml:mrow>
</mml:msubsup>
<mml:mrow>
<mml:mfenced open="(" close=")" separators="|">
<mml:mrow>
<mml:mi mathvariant="script">A</mml:mi>
</mml:mrow>
</mml:mfenced>
</mml:mrow>
<mml:mo>&#x2264;</mml:mo>
<mml:mfrac>
<mml:msubsup>
<mml:mi>q</mml:mi>
<mml:mi>h</mml:mi>
<mml:mn>2</mml:mn>
</mml:msubsup>
<mml:mrow>
<mml:mfenced open="|" close="|" separators="|">
<mml:mrow>
<mml:mi>H</mml:mi>
<mml:mi>A</mml:mi>
<mml:mi>S</mml:mi>
<mml:mi>H</mml:mi>
</mml:mrow>
</mml:mfenced>
</mml:mrow>
</mml:mfrac>
<mml:mo>&#x2b;</mml:mo>
<mml:msubsup>
<mml:mrow>
<mml:mn>2</mml:mn>
<mml:mi>A</mml:mi>
<mml:mi>d</mml:mi>
<mml:mi>v</mml:mi>
</mml:mrow>
<mml:mi mathvariant="script">A</mml:mi>
<mml:mtext>CMBDHP</mml:mtext>
</mml:msubsup>
<mml:mrow>
<mml:mfenced open="(" close=")" separators="|">
<mml:mrow>
<mml:mi>t</mml:mi>
</mml:mrow>
</mml:mfenced>
</mml:mrow>
</mml:mrow>
</mml:math>
<label>(9)</label>
</disp-formula>
</p>
<p>Based on the above proof, <inline-formula id="inf178">
<mml:math id="m209">
<mml:mrow>
<mml:mi mathvariant="script">A</mml:mi>
</mml:mrow>
</mml:math>
</inline-formula> is unable to win the game in probability polynomial time. Therefore, the proposed protocol has been formally analyzed and proven to be secure and effective.</p>
</statement>
</p>
</sec>
</sec>
<sec id="s6-2">
<title>5.2 Scyther tool analysis</title>
<p>Scyther is a protocol security analysis and verification tool [<xref ref-type="bibr" rid="B16">16</xref>]. This tool can use the Dolev-Yao attacker model and a strong security model to detect attack paths, which are illustrated graphically when found. To standardize the description of protocols and their security properties, Scyther provides a specialized description language called SPDL [<xref ref-type="bibr" rid="B40">40</xref>]. The following verification will utilize the Scyther tool and the Dolev-Yao attacker model.</p>
<p>In the protocol modeling of this paper, three roles are defined: U, TRC and SC, representing the tag, reader, and server, respectively. Secret, Alive, Weakagree, Niagree, and Nisynch are used to detect secret leakage, replay attacks and desynchronization attacks, respectively. The analysis results show that the Scyther tool could not identify any malicious attacks against the protocol presented in this paper, indicating that the protocol ensures the security of the secret information among the user, the trusted registration center, and the storage center. The Scyther tool analysis results are shown in <xref ref-type="fig" rid="F4">Figure 4</xref>.</p>
<fig id="F4" position="float">
<label>FIGURE 4</label>
<caption>
<p>Analysis results.</p>
</caption>
<graphic xlink:href="fphy-13-1522170-g004.tif"/>
</fig>
</sec>
<sec id="s6-3">
<title>5.3 Informal analysis</title>
<sec id="s6-3-1">
<title>5.3.1 User anonymity and untraceability</title>
<p>In the proposed scheme, on the one hand, no identity information is transmitted over the public channel. On the other hand, even if an attacker captures all the transmission information on the public channel, we use temporary identities for transmission, encrypted by <inline-formula id="inf179">
<mml:math id="m210">
<mml:mrow>
<mml:mi>P</mml:mi>
<mml:mi>I</mml:mi>
<mml:msub>
<mml:mi>D</mml:mi>
<mml:mi>i</mml:mi>
</mml:msub>
<mml:mo>&#x3d;</mml:mo>
<mml:mi>h</mml:mi>
<mml:mrow>
<mml:mfenced open="(" close=")" separators="|">
<mml:mrow>
<mml:mi>I</mml:mi>
<mml:msub>
<mml:mi>D</mml:mi>
<mml:mi>i</mml:mi>
</mml:msub>
<mml:mo>,</mml:mo>
<mml:mi>P</mml:mi>
<mml:msub>
<mml:mi>W</mml:mi>
<mml:mi>i</mml:mi>
</mml:msub>
<mml:mo>,</mml:mo>
<mml:msub>
<mml:mi>A</mml:mi>
<mml:mi>i</mml:mi>
</mml:msub>
</mml:mrow>
</mml:mfenced>
</mml:mrow>
<mml:mo>&#x2295;</mml:mo>
<mml:mi>P</mml:mi>
<mml:mi>I</mml:mi>
<mml:msubsup>
<mml:mi>D</mml:mi>
<mml:mi>i</mml:mi>
<mml:mo>&#x2a;</mml:mo>
</mml:msubsup>
</mml:mrow>
</mml:math>
</inline-formula>. To obtain the user&#x2019;s identity <inline-formula id="inf180">
<mml:math id="m211">
<mml:mrow>
<mml:mi>P</mml:mi>
<mml:mi>I</mml:mi>
<mml:msubsup>
<mml:mi>D</mml:mi>
<mml:mi>i</mml:mi>
<mml:mo>&#x2a;</mml:mo>
</mml:msubsup>
</mml:mrow>
</mml:math>
</inline-formula>, the attacker would need to know these values, but since they are secret, the attacker cannot obtain <inline-formula id="inf181">
<mml:math id="m212">
<mml:mrow>
<mml:mi>P</mml:mi>
<mml:mi>I</mml:mi>
<mml:msub>
<mml:mi>D</mml:mi>
<mml:mi>i</mml:mi>
</mml:msub>
</mml:mrow>
</mml:math>
</inline-formula>. Even if the attacker obtains <inline-formula id="inf182">
<mml:math id="m213">
<mml:mrow>
<mml:mi>P</mml:mi>
<mml:mi>I</mml:mi>
<mml:msub>
<mml:mi>D</mml:mi>
<mml:mi>i</mml:mi>
</mml:msub>
</mml:mrow>
</mml:math>
</inline-formula>, it is only a temporary identity, not the user&#x2019;s real identity. Since the random numbers <inline-formula id="inf183">
<mml:math id="m214">
<mml:mrow>
<mml:msub>
<mml:mi>c</mml:mi>
<mml:mi>i</mml:mi>
</mml:msub>
</mml:mrow>
</mml:math>
</inline-formula> and <inline-formula id="inf184">
<mml:math id="m215">
<mml:mrow>
<mml:msub>
<mml:mi>y</mml:mi>
<mml:mi>i</mml:mi>
</mml:msub>
</mml:mrow>
</mml:math>
</inline-formula> change with each session, and the computed authentication information is generated using these random numbers and timestamps, the information transmitted over the public channel is variable, making the user&#x2019;s information untraceable.</p>
</sec>
<sec id="s6-3-2">
<title>5.3.2 Privileged insider attack</title>
<p>Suppose a privileged insider becomes an attacker after obtaining the registration information of a legitimate user. Since the user&#x2019;s password is protected by secret values and hash functions, the privileged insider cannot obtain the plaintext of the user&#x2019;s password and cannot impersonate any party in the protocol.</p>
</sec>
<sec id="s6-3-3">
<title>5.3.3 User impersonation attack</title>
<p>To impersonate a legitimate <inline-formula id="inf185">
<mml:math id="m216">
<mml:mrow>
<mml:msub>
<mml:mi>U</mml:mi>
<mml:mi>i</mml:mi>
</mml:msub>
</mml:mrow>
</mml:math>
</inline-formula>, the attacker would have to obtain the user&#x2019;s identity identifier and password plaintext or forge the request information <inline-formula id="inf186">
<mml:math id="m217">
<mml:mrow>
<mml:mfenced open="{" close="}" separators="|">
<mml:mrow>
<mml:msub>
<mml:mi>V</mml:mi>
<mml:mn>1</mml:mn>
</mml:msub>
<mml:mo>,</mml:mo>
<mml:msub>
<mml:mi>V</mml:mi>
<mml:mn>3</mml:mn>
</mml:msub>
<mml:mo>,</mml:mo>
<mml:msub>
<mml:mi>V</mml:mi>
<mml:mn>4</mml:mn>
</mml:msub>
<mml:mo>,</mml:mo>
<mml:msub>
<mml:mi>V</mml:mi>
<mml:mn>5</mml:mn>
</mml:msub>
<mml:mo>,</mml:mo>
<mml:msub>
<mml:mi>V</mml:mi>
<mml:mn>6</mml:mn>
</mml:msub>
<mml:mo>,</mml:mo>
<mml:msub>
<mml:mi>T</mml:mi>
<mml:mn>1</mml:mn>
</mml:msub>
</mml:mrow>
</mml:mfenced>
</mml:mrow>
</mml:math>
</inline-formula>.First, based on the analysis of the offline password guessing attack, the attacker cannot obtain <inline-formula id="inf187">
<mml:math id="m218">
<mml:mrow>
<mml:mi>I</mml:mi>
<mml:msub>
<mml:mi>D</mml:mi>
<mml:mi>i</mml:mi>
</mml:msub>
</mml:mrow>
</mml:math>
</inline-formula> and <inline-formula id="inf188">
<mml:math id="m219">
<mml:mrow>
<mml:mi>P</mml:mi>
<mml:msub>
<mml:mi>W</mml:mi>
<mml:mi>i</mml:mi>
</mml:msub>
</mml:mrow>
</mml:math>
</inline-formula>. Second, since <inline-formula id="inf189">
<mml:math id="m220">
<mml:mrow>
<mml:msub>
<mml:mi>V</mml:mi>
<mml:mn>6</mml:mn>
</mml:msub>
</mml:mrow>
</mml:math>
</inline-formula> is derived from the concatenated hash of <inline-formula id="inf190">
<mml:math id="m221">
<mml:mrow>
<mml:mi>S</mml:mi>
<mml:mi>I</mml:mi>
<mml:msub>
<mml:mi>D</mml:mi>
<mml:mi>j</mml:mi>
</mml:msub>
<mml:mo>,</mml:mo>
<mml:mi>I</mml:mi>
<mml:msub>
<mml:mi>D</mml:mi>
<mml:mi>i</mml:mi>
</mml:msub>
<mml:mo>,</mml:mo>
<mml:msub>
<mml:mi>V</mml:mi>
<mml:mn>2</mml:mn>
</mml:msub>
<mml:mo>,</mml:mo>
<mml:msub>
<mml:mi>y</mml:mi>
<mml:mi>i</mml:mi>
</mml:msub>
<mml:mo>,</mml:mo>
<mml:msub>
<mml:mi>A</mml:mi>
<mml:mi>i</mml:mi>
</mml:msub>
</mml:mrow>
</mml:math>
</inline-formula> and <inline-formula id="inf191">
<mml:math id="m222">
<mml:mrow>
<mml:msub>
<mml:mi>T</mml:mi>
<mml:mn>1</mml:mn>
</mml:msub>
</mml:mrow>
</mml:math>
</inline-formula>, the attacker cannot forge <inline-formula id="inf192">
<mml:math id="m223">
<mml:mrow>
<mml:msub>
<mml:mi>V</mml:mi>
<mml:mn>2</mml:mn>
</mml:msub>
</mml:mrow>
</mml:math>
</inline-formula> and <inline-formula id="inf193">
<mml:math id="m224">
<mml:mrow>
<mml:msub>
<mml:mi>A</mml:mi>
<mml:mi>i</mml:mi>
</mml:msub>
</mml:mrow>
</mml:math>
</inline-formula>.Therefore, the proposed protocol is immune to user impersonation attacks.</p>
</sec>
<sec id="s6-3-4">
<title>5.3.4 Storage center impersonation attack</title>
<p>Since <inline-formula id="inf194">
<mml:math id="m225">
<mml:mrow>
<mml:msub>
<mml:mi>B</mml:mi>
<mml:mi>j</mml:mi>
</mml:msub>
</mml:mrow>
</mml:math>
</inline-formula> is the long-term private key of the storage center <inline-formula id="inf195">
<mml:math id="m226">
<mml:mrow>
<mml:msub>
<mml:mrow>
<mml:mi>S</mml:mi>
<mml:mi>C</mml:mi>
</mml:mrow>
<mml:mi>j</mml:mi>
</mml:msub>
</mml:mrow>
</mml:math>
</inline-formula> and is unknown to adversaries, the attacker cannot compute the correct <inline-formula id="inf196">
<mml:math id="m227">
<mml:mrow>
<mml:msub>
<mml:mi>V</mml:mi>
<mml:mn>11</mml:mn>
</mml:msub>
</mml:mrow>
</mml:math>
</inline-formula>, and thus cannot forge <inline-formula id="inf197">
<mml:math id="m228">
<mml:mrow>
<mml:msub>
<mml:mi>V</mml:mi>
<mml:mn>12</mml:mn>
</mml:msub>
</mml:mrow>
</mml:math>
</inline-formula> to generate a legitimate response message corresponding to the user&#x2019;s request. Therefore, the proposed scheme is immune to storage center impersonation attacks.</p>
</sec>
<sec id="s6-3-5">
<title>5.3.5 Replay attack</title>
<p>The scheme uses random numbers and timestamps to defend against replay attacks. Suppose an attacker attempts to replay request messages <inline-formula id="inf198">
<mml:math id="m229">
<mml:mrow>
<mml:mfenced open="{" close="}" separators="|">
<mml:mrow>
<mml:msub>
<mml:mi>V</mml:mi>
<mml:mn>1</mml:mn>
</mml:msub>
<mml:mo>,</mml:mo>
<mml:msub>
<mml:mi>V</mml:mi>
<mml:mn>3</mml:mn>
</mml:msub>
<mml:mo>,</mml:mo>
<mml:msub>
<mml:mi>V</mml:mi>
<mml:mn>4</mml:mn>
</mml:msub>
<mml:mo>,</mml:mo>
<mml:msub>
<mml:mi>V</mml:mi>
<mml:mn>5</mml:mn>
</mml:msub>
<mml:mo>,</mml:mo>
<mml:msub>
<mml:mi>V</mml:mi>
<mml:mn>6</mml:mn>
</mml:msub>
<mml:mo>,</mml:mo>
<mml:msub>
<mml:mi>T</mml:mi>
<mml:mn>1</mml:mn>
</mml:msub>
</mml:mrow>
</mml:mfenced>
</mml:mrow>
</mml:math>
</inline-formula>, <inline-formula id="inf199">
<mml:math id="m230">
<mml:mrow>
<mml:mfenced open="" close="}" separators="|">
<mml:mrow>
<mml:msub>
<mml:mrow>
<mml:msub>
<mml:mrow>
<mml:mfenced open="{" close="" separators="|">
<mml:mrow>
<mml:mi>S</mml:mi>
<mml:mi>I</mml:mi>
<mml:mi>D</mml:mi>
<mml:mo>&#x2a;</mml:mo>
</mml:mrow>
</mml:mfenced>
</mml:mrow>
<mml:mi>j</mml:mi>
</mml:msub>
<mml:mo>,</mml:mo>
<mml:mi>V</mml:mi>
</mml:mrow>
<mml:mn>1</mml:mn>
</mml:msub>
<mml:mo>,</mml:mo>
<mml:msub>
<mml:mi>V</mml:mi>
<mml:mn>7</mml:mn>
</mml:msub>
<mml:mo>,</mml:mo>
<mml:msub>
<mml:mi>V</mml:mi>
<mml:mn>8</mml:mn>
</mml:msub>
<mml:mo>,</mml:mo>
<mml:msub>
<mml:mi>V</mml:mi>
<mml:mn>9</mml:mn>
</mml:msub>
<mml:mo>,</mml:mo>
<mml:msub>
<mml:mi>T</mml:mi>
<mml:mn>1</mml:mn>
</mml:msub>
</mml:mrow>
</mml:mfenced>
</mml:mrow>
</mml:math>
</inline-formula>,and <inline-formula id="inf200">
<mml:math id="m231">
<mml:mrow>
<mml:mfenced open="{" close="}" separators="|">
<mml:mrow>
<mml:msub>
<mml:mi>V</mml:mi>
<mml:mn>10</mml:mn>
</mml:msub>
<mml:mo>,</mml:mo>
<mml:msub>
<mml:mi>V</mml:mi>
<mml:mn>12</mml:mn>
</mml:msub>
<mml:mo>,</mml:mo>
<mml:msub>
<mml:mi>T</mml:mi>
<mml:mn>3</mml:mn>
</mml:msub>
</mml:mrow>
</mml:mfenced>
</mml:mrow>
</mml:math>
</inline-formula>. Since the random numbers and timestamps are variable and random in each session, replayed messages cannot pass the verification by the storage center <inline-formula id="inf201">
<mml:math id="m232">
<mml:mrow>
<mml:msub>
<mml:mrow>
<mml:mi>S</mml:mi>
<mml:mi>C</mml:mi>
</mml:mrow>
<mml:mi>j</mml:mi>
</mml:msub>
</mml:mrow>
</mml:math>
</inline-formula> and will result in session termination. Similarly, due to the characteristics of random numbers and timestamps, replayed messages cannot pass the user&#x2019;s detection, leading to session termination. Additionally, even if the attacker replays previous messages, the difficult problem prevents the attacker from calculating a valid session key. Therefore, the proposed protocol is resistant to replay attacks.</p>
</sec>
<sec id="s6-3-6">
<title>5.3.6 Man-in-the-middle attack</title>
<p>Suppose an attacker attempts to intercept and tamper with messages <inline-formula id="inf202">
<mml:math id="m233">
<mml:mrow>
<mml:mfenced open="{" close="}" separators="|">
<mml:mrow>
<mml:msub>
<mml:mi>V</mml:mi>
<mml:mn>1</mml:mn>
</mml:msub>
<mml:mo>,</mml:mo>
<mml:msub>
<mml:mi>V</mml:mi>
<mml:mn>3</mml:mn>
</mml:msub>
<mml:mo>,</mml:mo>
<mml:msub>
<mml:mi>V</mml:mi>
<mml:mn>4</mml:mn>
</mml:msub>
<mml:mo>,</mml:mo>
<mml:msub>
<mml:mi>V</mml:mi>
<mml:mn>5</mml:mn>
</mml:msub>
<mml:mo>,</mml:mo>
<mml:msub>
<mml:mi>V</mml:mi>
<mml:mn>6</mml:mn>
</mml:msub>
<mml:mo>,</mml:mo>
<mml:msub>
<mml:mi>T</mml:mi>
<mml:mn>1</mml:mn>
</mml:msub>
</mml:mrow>
</mml:mfenced>
</mml:mrow>
</mml:math>
</inline-formula>, <inline-formula id="inf203">
<mml:math id="m234">
<mml:mrow>
<mml:mfenced open="" close="}" separators="|">
<mml:mrow>
<mml:msub>
<mml:mrow>
<mml:msubsup>
<mml:mrow>
<mml:mfenced open="{" close="" separators="|">
<mml:mrow>
<mml:mi>S</mml:mi>
<mml:mi>I</mml:mi>
<mml:mi>D</mml:mi>
</mml:mrow>
</mml:mfenced>
</mml:mrow>
<mml:mi>j</mml:mi>
<mml:mo>&#x2a;</mml:mo>
</mml:msubsup>
<mml:mo>,</mml:mo>
<mml:mi>V</mml:mi>
</mml:mrow>
<mml:mn>1</mml:mn>
</mml:msub>
<mml:mo>,</mml:mo>
<mml:msub>
<mml:mi>V</mml:mi>
<mml:mn>7</mml:mn>
</mml:msub>
<mml:mo>,</mml:mo>
<mml:msub>
<mml:mi>V</mml:mi>
<mml:mn>8</mml:mn>
</mml:msub>
<mml:mo>,</mml:mo>
<mml:msub>
<mml:mi>V</mml:mi>
<mml:mn>9</mml:mn>
</mml:msub>
<mml:mo>,</mml:mo>
<mml:msub>
<mml:mi>T</mml:mi>
<mml:mn>1</mml:mn>
</mml:msub>
</mml:mrow>
</mml:mfenced>
</mml:mrow>
</mml:math>
</inline-formula>, and <inline-formula id="inf204">
<mml:math id="m235">
<mml:mrow>
<mml:mfenced open="{" close="}" separators="|">
<mml:mrow>
<mml:msub>
<mml:mi>V</mml:mi>
<mml:mn>10</mml:mn>
</mml:msub>
<mml:mo>,</mml:mo>
<mml:msub>
<mml:mi>V</mml:mi>
<mml:mn>12</mml:mn>
</mml:msub>
<mml:mo>,</mml:mo>
<mml:msub>
<mml:mi>T</mml:mi>
<mml:mn>3</mml:mn>
</mml:msub>
</mml:mrow>
</mml:mfenced>
</mml:mrow>
</mml:math>
</inline-formula>, making participants believe the received information is authentic. The attacker would need to obtain the parameters <inline-formula id="inf205">
<mml:math id="m236">
<mml:mrow>
<mml:msub>
<mml:mi>V</mml:mi>
<mml:mn>2</mml:mn>
</mml:msub>
</mml:mrow>
</mml:math>
</inline-formula> and <inline-formula id="inf206">
<mml:math id="m237">
<mml:mrow>
<mml:msub>
<mml:mi>A</mml:mi>
<mml:mi>i</mml:mi>
</mml:msub>
</mml:mrow>
</mml:math>
</inline-formula> to calculate <inline-formula id="inf207">
<mml:math id="m238">
<mml:mrow>
<mml:msub>
<mml:mi>V</mml:mi>
<mml:mn>3</mml:mn>
</mml:msub>
<mml:mo>,</mml:mo>
<mml:msub>
<mml:mi>V</mml:mi>
<mml:mn>4</mml:mn>
</mml:msub>
<mml:mo>,</mml:mo>
<mml:msub>
<mml:mi>V</mml:mi>
<mml:mn>5</mml:mn>
</mml:msub>
<mml:mo>,</mml:mo>
<mml:msub>
<mml:mi>V</mml:mi>
<mml:mn>6</mml:mn>
</mml:msub>
</mml:mrow>
</mml:math>
</inline-formula> and modify the message <inline-formula id="inf208">
<mml:math id="m239">
<mml:mrow>
<mml:mfenced open="{" close="}" separators="|">
<mml:mrow>
<mml:msub>
<mml:mi>V</mml:mi>
<mml:mn>1</mml:mn>
</mml:msub>
<mml:mo>,</mml:mo>
<mml:msub>
<mml:mi>V</mml:mi>
<mml:mn>3</mml:mn>
</mml:msub>
<mml:mo>,</mml:mo>
<mml:msub>
<mml:mi>V</mml:mi>
<mml:mn>4</mml:mn>
</mml:msub>
<mml:mo>,</mml:mo>
<mml:msub>
<mml:mi>V</mml:mi>
<mml:mn>5</mml:mn>
</mml:msub>
<mml:mo>,</mml:mo>
<mml:msub>
<mml:mi>V</mml:mi>
<mml:mn>6</mml:mn>
</mml:msub>
<mml:mo>,</mml:mo>
<mml:msub>
<mml:mi>T</mml:mi>
<mml:mn>1</mml:mn>
</mml:msub>
</mml:mrow>
</mml:mfenced>
</mml:mrow>
</mml:math>
</inline-formula>. Similarly, the attacker cannot modify other messages <inline-formula id="inf209">
<mml:math id="m240">
<mml:mrow>
<mml:mfenced open="" close="}" separators="|">
<mml:mrow>
<mml:msub>
<mml:mrow>
<mml:msubsup>
<mml:mrow>
<mml:mfenced open="{" close="" separators="|">
<mml:mrow>
<mml:mi>S</mml:mi>
<mml:mi>I</mml:mi>
<mml:mi>D</mml:mi>
</mml:mrow>
</mml:mfenced>
</mml:mrow>
<mml:mi>j</mml:mi>
<mml:mo>&#x2a;</mml:mo>
</mml:msubsup>
<mml:mo>,</mml:mo>
<mml:mi>V</mml:mi>
</mml:mrow>
<mml:mn>1</mml:mn>
</mml:msub>
<mml:mo>,</mml:mo>
<mml:msub>
<mml:mi>V</mml:mi>
<mml:mn>7</mml:mn>
</mml:msub>
<mml:mo>,</mml:mo>
<mml:msub>
<mml:mi>V</mml:mi>
<mml:mn>8</mml:mn>
</mml:msub>
<mml:mo>,</mml:mo>
<mml:msub>
<mml:mi>V</mml:mi>
<mml:mn>9</mml:mn>
</mml:msub>
<mml:mo>,</mml:mo>
<mml:msub>
<mml:mi>T</mml:mi>
<mml:mn>1</mml:mn>
</mml:msub>
</mml:mrow>
</mml:mfenced>
</mml:mrow>
</mml:math>
</inline-formula> and <inline-formula id="inf210">
<mml:math id="m241">
<mml:mrow>
<mml:mfenced open="{" close="}" separators="|">
<mml:mrow>
<mml:msub>
<mml:mi>V</mml:mi>
<mml:mn>10</mml:mn>
</mml:msub>
<mml:mo>,</mml:mo>
<mml:msub>
<mml:mi>V</mml:mi>
<mml:mn>12</mml:mn>
</mml:msub>
<mml:mo>,</mml:mo>
<mml:msub>
<mml:mi>T</mml:mi>
<mml:mn>3</mml:mn>
</mml:msub>
</mml:mrow>
</mml:mfenced>
</mml:mrow>
</mml:math>
</inline-formula>. Therefore, this scheme can resist man-in-the-middle attacks.</p>
</sec>
<sec id="s6-3-7">
<title>5.3.7 Mutual authentication</title>
<p>In the proposed scheme, to authenticate <inline-formula id="inf211">
<mml:math id="m242">
<mml:mrow>
<mml:msub>
<mml:mi>U</mml:mi>
<mml:mi>i</mml:mi>
</mml:msub>
</mml:mrow>
</mml:math>
</inline-formula>, the TRC first verifies the correctness of the message <inline-formula id="inf212">
<mml:math id="m243">
<mml:mrow>
<mml:msubsup>
<mml:mi mathvariant="normal">V</mml:mi>
<mml:mn>6</mml:mn>
<mml:mo>&#x2a;</mml:mo>
</mml:msubsup>
<mml:mo>&#x3d;</mml:mo>
<mml:msub>
<mml:mi>V</mml:mi>
<mml:mn>6</mml:mn>
</mml:msub>
</mml:mrow>
</mml:math>
</inline-formula>. If the message passes verification, the TRC can authenticate that the communication requester is <inline-formula id="inf213">
<mml:math id="m244">
<mml:mrow>
<mml:msub>
<mml:mi>U</mml:mi>
<mml:mi>i</mml:mi>
</mml:msub>
</mml:mrow>
</mml:math>
</inline-formula>. To authenticate the TRC, <inline-formula id="inf214">
<mml:math id="m245">
<mml:mrow>
<mml:msub>
<mml:mrow>
<mml:mi>S</mml:mi>
<mml:mi>C</mml:mi>
</mml:mrow>
<mml:mi>j</mml:mi>
</mml:msub>
</mml:mrow>
</mml:math>
</inline-formula> first verifies the correctness of the message <inline-formula id="inf215">
<mml:math id="m246">
<mml:mrow>
<mml:msubsup>
<mml:mi mathvariant="normal">V</mml:mi>
<mml:mn>9</mml:mn>
<mml:mo>&#x2a;</mml:mo>
</mml:msubsup>
<mml:mo>&#x3d;</mml:mo>
<mml:msub>
<mml:mi>V</mml:mi>
<mml:mn>9</mml:mn>
</mml:msub>
</mml:mrow>
</mml:math>
</inline-formula>. If the message fails verification, <inline-formula id="inf216">
<mml:math id="m247">
<mml:mrow>
<mml:msub>
<mml:mrow>
<mml:mi>S</mml:mi>
<mml:mi>C</mml:mi>
</mml:mrow>
<mml:mi>j</mml:mi>
</mml:msub>
</mml:mrow>
</mml:math>
</inline-formula> rejects the communication request. Otherwise, <inline-formula id="inf217">
<mml:math id="m248">
<mml:mrow>
<mml:msub>
<mml:mrow>
<mml:mi>S</mml:mi>
<mml:mi>C</mml:mi>
</mml:mrow>
<mml:mi>j</mml:mi>
</mml:msub>
</mml:mrow>
</mml:math>
</inline-formula> can authenticate that the communication requester is the TRC. To authenticate <inline-formula id="inf218">
<mml:math id="m249">
<mml:mrow>
<mml:msub>
<mml:mrow>
<mml:mi>S</mml:mi>
<mml:mi>C</mml:mi>
</mml:mrow>
<mml:mi>j</mml:mi>
</mml:msub>
</mml:mrow>
</mml:math>
</inline-formula>, <inline-formula id="inf219">
<mml:math id="m250">
<mml:mrow>
<mml:msub>
<mml:mi>U</mml:mi>
<mml:mi>i</mml:mi>
</mml:msub>
</mml:mrow>
</mml:math>
</inline-formula> computes the verification message <inline-formula id="inf220">
<mml:math id="m251">
<mml:mrow>
<mml:msubsup>
<mml:mi>V</mml:mi>
<mml:mn>12</mml:mn>
<mml:mo>&#x2a;</mml:mo>
</mml:msubsup>
</mml:mrow>
</mml:math>
</inline-formula> and verifies the correctness of <inline-formula id="inf221">
<mml:math id="m252">
<mml:mrow>
<mml:msubsup>
<mml:mi>V</mml:mi>
<mml:mn>12</mml:mn>
<mml:mo>&#x2a;</mml:mo>
</mml:msubsup>
<mml:mo>&#x3d;</mml:mo>
<mml:msub>
<mml:mi>V</mml:mi>
<mml:mn>12</mml:mn>
</mml:msub>
</mml:mrow>
</mml:math>
</inline-formula>. If the message passes verification, <inline-formula id="inf222">
<mml:math id="m253">
<mml:mrow>
<mml:msub>
<mml:mi>U</mml:mi>
<mml:mi>i</mml:mi>
</mml:msub>
</mml:mrow>
</mml:math>
</inline-formula> can authenticate that the communication requester is <inline-formula id="inf223">
<mml:math id="m254">
<mml:mrow>
<mml:msub>
<mml:mrow>
<mml:mi>S</mml:mi>
<mml:mi>C</mml:mi>
</mml:mrow>
<mml:mi>j</mml:mi>
</mml:msub>
</mml:mrow>
</mml:math>
</inline-formula>, and the session key is also verified. Otherwise, <inline-formula id="inf224">
<mml:math id="m255">
<mml:mrow>
<mml:msub>
<mml:mi>U</mml:mi>
<mml:mi>i</mml:mi>
</mml:msub>
</mml:mrow>
</mml:math>
</inline-formula> rejects the communication request. Therefore, the proposed protocol provides mutual authentication functionality.</p>
</sec>
<sec id="s6-3-8">
<title>5.3.8 Forward security</title>
<p>The session key ultimately negotiated in the proposed scheme, <inline-formula id="inf225">
<mml:math id="m256">
<mml:mrow>
<mml:mi>S</mml:mi>
<mml:msub>
<mml:mi>K</mml:mi>
<mml:mi>i</mml:mi>
</mml:msub>
<mml:mo>&#x3d;</mml:mo>
<mml:mi>H</mml:mi>
<mml:mrow>
<mml:mfenced open="(" close=")" separators="|">
<mml:mrow>
<mml:mi>P</mml:mi>
<mml:mi>I</mml:mi>
<mml:msub>
<mml:mi>D</mml:mi>
<mml:mi>i</mml:mi>
</mml:msub>
<mml:mo>,</mml:mo>
<mml:mi>S</mml:mi>
<mml:mi>I</mml:mi>
<mml:msub>
<mml:mi>D</mml:mi>
<mml:mi>j</mml:mi>
</mml:msub>
<mml:mo>,</mml:mo>
<mml:msubsup>
<mml:mi mathvariant="normal">V</mml:mi>
<mml:mn>11</mml:mn>
<mml:mo>&#x2a;</mml:mo>
</mml:msubsup>
<mml:mo>,</mml:mo>
<mml:msub>
<mml:mi>T</mml:mi>
<mml:mn>3</mml:mn>
</mml:msub>
</mml:mrow>
</mml:mfenced>
</mml:mrow>
</mml:mrow>
</mml:math>
</inline-formula>, is independently calculated by both parties in the protocol and is unrelated to the user&#x2019;s password or long-term private key. Even if an attacker intercepts <inline-formula id="inf226">
<mml:math id="m257">
<mml:mrow>
<mml:mfenced open="{" close="}" separators="|">
<mml:mrow>
<mml:msub>
<mml:mi>V</mml:mi>
<mml:mn>1</mml:mn>
</mml:msub>
<mml:mo>,</mml:mo>
<mml:msub>
<mml:mi>V</mml:mi>
<mml:mn>3</mml:mn>
</mml:msub>
<mml:mo>,</mml:mo>
<mml:msub>
<mml:mi>V</mml:mi>
<mml:mn>4</mml:mn>
</mml:msub>
<mml:mo>,</mml:mo>
<mml:msub>
<mml:mi>V</mml:mi>
<mml:mn>5</mml:mn>
</mml:msub>
<mml:mo>,</mml:mo>
<mml:msub>
<mml:mi>V</mml:mi>
<mml:mn>6</mml:mn>
</mml:msub>
<mml:mo>,</mml:mo>
<mml:msub>
<mml:mi>T</mml:mi>
<mml:mn>1</mml:mn>
</mml:msub>
</mml:mrow>
</mml:mfenced>
</mml:mrow>
</mml:math>
</inline-formula>, <inline-formula id="inf227">
<mml:math id="m258">
<mml:mrow>
<mml:mfenced open="{" close="}" separators="|">
<mml:mrow>
<mml:msub>
<mml:mrow>
<mml:msubsup>
<mml:mrow>
<mml:mi>S</mml:mi>
<mml:mi>I</mml:mi>
<mml:mi>D</mml:mi>
</mml:mrow>
<mml:mi>j</mml:mi>
<mml:mo>&#x2a;</mml:mo>
</mml:msubsup>
<mml:mo>,</mml:mo>
<mml:mi>V</mml:mi>
</mml:mrow>
<mml:mn>1</mml:mn>
</mml:msub>
<mml:mo>,</mml:mo>
<mml:msub>
<mml:mi>V</mml:mi>
<mml:mn>7</mml:mn>
</mml:msub>
<mml:mo>,</mml:mo>
<mml:msub>
<mml:mi>V</mml:mi>
<mml:mn>8</mml:mn>
</mml:msub>
<mml:mo>,</mml:mo>
<mml:msub>
<mml:mi>V</mml:mi>
<mml:mn>9</mml:mn>
</mml:msub>
<mml:mo>,</mml:mo>
<mml:msub>
<mml:mi>T</mml:mi>
<mml:mn>1</mml:mn>
</mml:msub>
</mml:mrow>
</mml:mfenced>
</mml:mrow>
</mml:math>
</inline-formula>, and <inline-formula id="inf228">
<mml:math id="m259">
<mml:mrow>
<mml:mfenced open="{" close="}" separators="|">
<mml:mrow>
<mml:msub>
<mml:mi>V</mml:mi>
<mml:mn>10</mml:mn>
</mml:msub>
<mml:mo>,</mml:mo>
<mml:msub>
<mml:mi>V</mml:mi>
<mml:mn>12</mml:mn>
</mml:msub>
<mml:mo>,</mml:mo>
<mml:msub>
<mml:mi>T</mml:mi>
<mml:mn>3</mml:mn>
</mml:msub>
</mml:mrow>
</mml:mfenced>
</mml:mrow>
</mml:math>
</inline-formula>, they still cannot compute the session key. Moreover, due to the difficult problem, the attacker cannot derive <inline-formula id="inf229">
<mml:math id="m260">
<mml:mrow>
<mml:msubsup>
<mml:mi mathvariant="normal">V</mml:mi>
<mml:mn>11</mml:mn>
<mml:mo>&#x2a;</mml:mo>
</mml:msubsup>
<mml:mo>&#x3d;</mml:mo>
<mml:msub>
<mml:mi mathvariant="normal">T</mml:mi>
<mml:msub>
<mml:mi>c</mml:mi>
<mml:mi>i</mml:mi>
</mml:msub>
</mml:msub>
<mml:mrow>
<mml:mfenced open="(" close=")" separators="|">
<mml:mrow>
<mml:msub>
<mml:mi>V</mml:mi>
<mml:mn>10</mml:mn>
</mml:msub>
</mml:mrow>
</mml:mfenced>
</mml:mrow>
<mml:mtext>&#x2009;</mml:mtext>
<mml:mi mathvariant="italic">mod</mml:mi>
<mml:mtext>&#x2009;</mml:mtext>
<mml:mi>p</mml:mi>
</mml:mrow>
</mml:math>
</inline-formula> from <inline-formula id="inf230">
<mml:math id="m261">
<mml:mrow>
<mml:msub>
<mml:mi>V</mml:mi>
<mml:mn>10</mml:mn>
</mml:msub>
<mml:mo>&#x3d;</mml:mo>
<mml:msub>
<mml:mi mathvariant="normal">T</mml:mi>
<mml:msub>
<mml:mi>e</mml:mi>
<mml:mi>j</mml:mi>
</mml:msub>
</mml:msub>
<mml:mrow>
<mml:mfenced open="(" close=")" separators="|">
<mml:mrow>
<mml:mi>x</mml:mi>
</mml:mrow>
</mml:mfenced>
</mml:mrow>
<mml:mtext>&#x2009;</mml:mtext>
<mml:mi mathvariant="italic">mod</mml:mi>
<mml:mtext>&#x2009;</mml:mtext>
<mml:mi>p</mml:mi>
</mml:mrow>
</mml:math>
</inline-formula>. Therefore, the scheme ensures the security of the session key.</p>
</sec>
<sec id="s6-3-9">
<title>5.3.9 Session key security</title>
<p>Only legitimate <inline-formula id="inf231">
<mml:math id="m262">
<mml:mrow>
<mml:msub>
<mml:mi>U</mml:mi>
<mml:mi>i</mml:mi>
</mml:msub>
</mml:mrow>
</mml:math>
</inline-formula> and <inline-formula id="inf232">
<mml:math id="m263">
<mml:mrow>
<mml:msub>
<mml:mrow>
<mml:mi>S</mml:mi>
<mml:mi>C</mml:mi>
</mml:mrow>
<mml:mi>j</mml:mi>
</mml:msub>
</mml:mrow>
</mml:math>
</inline-formula> will negotiate a session key <inline-formula id="inf233">
<mml:math id="m264">
<mml:mrow>
<mml:mi>S</mml:mi>
<mml:msub>
<mml:mi>K</mml:mi>
<mml:mi>i</mml:mi>
</mml:msub>
<mml:mo>&#x3d;</mml:mo>
<mml:mi>H</mml:mi>
<mml:mrow>
<mml:mfenced open="(" close=")" separators="|">
<mml:mrow>
<mml:mi>P</mml:mi>
<mml:mi>I</mml:mi>
<mml:msub>
<mml:mi>D</mml:mi>
<mml:mi>i</mml:mi>
</mml:msub>
<mml:mo>,</mml:mo>
<mml:mi>S</mml:mi>
<mml:mi>I</mml:mi>
<mml:msub>
<mml:mi>D</mml:mi>
<mml:mi>j</mml:mi>
</mml:msub>
<mml:mo>,</mml:mo>
<mml:msubsup>
<mml:mi mathvariant="normal">V</mml:mi>
<mml:mn>11</mml:mn>
<mml:mo>&#x2a;</mml:mo>
</mml:msubsup>
<mml:mo>,</mml:mo>
<mml:msub>
<mml:mi>T</mml:mi>
<mml:mn>3</mml:mn>
</mml:msub>
</mml:mrow>
</mml:mfenced>
</mml:mrow>
</mml:mrow>
</mml:math>
</inline-formula> for communication after the authentication process. Since the session key includes <inline-formula id="inf234">
<mml:math id="m265">
<mml:mrow>
<mml:msub>
<mml:mi>T</mml:mi>
<mml:mn>3</mml:mn>
</mml:msub>
</mml:mrow>
</mml:math>
</inline-formula>, which indicates the freshness of each communication, even if the session key is compromised, an attacker cannot use this key to recover previous or future session keys.</p>
</sec>
</sec>
</sec>
<sec id="s7">
<title>6 Performance analysis</title>
<sec id="s7-1">
<title>6.1 Computation overhead comparison</title>
<p>
<xref ref-type="table" rid="T2">Table 2</xref> summarizes the computation overhead of several protocols, where <inline-formula id="inf235">
<mml:math id="m266">
<mml:mrow>
<mml:msub>
<mml:mi>T</mml:mi>
<mml:mrow>
<mml:mi>e</mml:mi>
<mml:mi>c</mml:mi>
<mml:mi>m</mml:mi>
</mml:mrow>
</mml:msub>
</mml:mrow>
</mml:math>
</inline-formula> represents the time for ECC point multiplication, <inline-formula id="inf236">
<mml:math id="m267">
<mml:mrow>
<mml:msub>
<mml:mi>T</mml:mi>
<mml:mrow>
<mml:mi>f</mml:mi>
<mml:mi>e</mml:mi>
</mml:mrow>
</mml:msub>
</mml:mrow>
</mml:math>
</inline-formula> represents the time for fuzzy extraction operations, <inline-formula id="inf237">
<mml:math id="m268">
<mml:mrow>
<mml:msub>
<mml:mi>T</mml:mi>
<mml:mi>h</mml:mi>
</mml:msub>
</mml:mrow>
</mml:math>
</inline-formula> represents the time for a one-way hash function, <inline-formula id="inf238">
<mml:math id="m269">
<mml:mrow>
<mml:msub>
<mml:mi>T</mml:mi>
<mml:mrow>
<mml:mi>E</mml:mi>
<mml:mo>/</mml:mo>
<mml:mi>D</mml:mi>
</mml:mrow>
</mml:msub>
</mml:mrow>
</mml:math>
</inline-formula> represents the time for encryption/decryption using symmetric encryption techniques and <inline-formula id="inf239">
<mml:math id="m270">
<mml:mrow>
<mml:msub>
<mml:mi>T</mml:mi>
<mml:mrow>
<mml:mi>c</mml:mi>
<mml:mi>m</mml:mi>
</mml:mrow>
</mml:msub>
</mml:mrow>
</mml:math>
</inline-formula> represents the time for chebyshev chaotic map operation. <xref ref-type="table" rid="T2">Table 2</xref> summarizes the computation overhead of the proposed scheme and other schemes by Chang [<xref ref-type="bibr" rid="B41">41</xref>], Wazid [<xref ref-type="bibr" rid="B42">42</xref>] and Li [<xref ref-type="bibr" rid="B43">43</xref>]. For the cryptographic operations involved in the proposed scheme and other related schemes, network simulation experiments were conducted on a hardware platform configured with 8GB memory, an Intel Core i7 processor, and an Ubuntu 16 system. The execution times for the relevant operations were calculated using the widely applied cryptographic PBC library. Through this experiment, the execution times of various cryptographic operations were obtained. The running times for different operations are as follows: <inline-formula id="inf240">
<mml:math id="m271">
<mml:mrow>
<mml:msub>
<mml:mi>T</mml:mi>
<mml:mrow>
<mml:mi>e</mml:mi>
<mml:mi>c</mml:mi>
<mml:mi>m</mml:mi>
</mml:mrow>
</mml:msub>
</mml:mrow>
</mml:math>
</inline-formula> is approximately 71.23 ms, <inline-formula id="inf241">
<mml:math id="m272">
<mml:mrow>
<mml:msub>
<mml:mi>T</mml:mi>
<mml:mi>h</mml:mi>
</mml:msub>
</mml:mrow>
</mml:math>
</inline-formula> is approximately 0.45 ms, <inline-formula id="inf242">
<mml:math id="m273">
<mml:mrow>
<mml:msub>
<mml:mi>T</mml:mi>
<mml:mrow>
<mml:mi>j</mml:mi>
<mml:mi>e</mml:mi>
</mml:mrow>
</mml:msub>
</mml:mrow>
</mml:math>
</inline-formula> is approximately 71.23 ms, <inline-formula id="inf243">
<mml:math id="m274">
<mml:mrow>
<mml:msub>
<mml:mi>T</mml:mi>
<mml:mrow>
<mml:mi>D</mml:mi>
<mml:mo>/</mml:mo>
<mml:mi>E</mml:mi>
</mml:mrow>
</mml:msub>
</mml:mrow>
</mml:math>
</inline-formula> is approximately 6.86 ms, and <inline-formula id="inf244">
<mml:math id="m275">
<mml:mrow>
<mml:msub>
<mml:mi>T</mml:mi>
<mml:mrow>
<mml:mi>c</mml:mi>
<mml:mi>m</mml:mi>
</mml:mrow>
</mml:msub>
</mml:mrow>
</mml:math>
</inline-formula> is approximately 18.61 s.</p>
<table-wrap id="T2" position="float">
<label>TABLE 2</label>
<caption>
<p>Computation overhead.</p>
</caption>
<table>
<thead valign="top">
<tr>
<th align="left">Scheme</th>
<th align="center">User</th>
<th align="center">TRC</th>
<th align="center">SC</th>
<th align="center">Total</th>
</tr>
</thead>
<tbody valign="top">
<tr>
<td align="left">[<xref ref-type="bibr" rid="B41">41</xref>]</td>
<td align="center">
<inline-formula id="inf245">
<mml:math id="m276">
<mml:mrow>
<mml:mn>2</mml:mn>
<mml:msub>
<mml:mi>T</mml:mi>
<mml:mrow>
<mml:mi>e</mml:mi>
<mml:mi>c</mml:mi>
<mml:mi>m</mml:mi>
</mml:mrow>
</mml:msub>
<mml:mo>&#x2b;</mml:mo>
<mml:mn>7</mml:mn>
<mml:msub>
<mml:mi>T</mml:mi>
<mml:mi>h</mml:mi>
</mml:msub>
</mml:mrow>
</mml:math>
</inline-formula>
</td>
<td align="center">
<inline-formula id="inf246">
<mml:math id="m277">
<mml:mrow>
<mml:mn>9</mml:mn>
<mml:msub>
<mml:mi>T</mml:mi>
<mml:mi>h</mml:mi>
</mml:msub>
</mml:mrow>
</mml:math>
</inline-formula>
</td>
<td align="center">
<inline-formula id="inf247">
<mml:math id="m278">
<mml:mrow>
<mml:mn>2</mml:mn>
<mml:msub>
<mml:mi>T</mml:mi>
<mml:mrow>
<mml:mi>e</mml:mi>
<mml:mi>c</mml:mi>
<mml:mi>m</mml:mi>
</mml:mrow>
</mml:msub>
<mml:mo>&#x2b;</mml:mo>
<mml:mn>5</mml:mn>
<mml:msub>
<mml:mi>T</mml:mi>
<mml:mi>h</mml:mi>
</mml:msub>
</mml:mrow>
</mml:math>
</inline-formula>
</td>
<td align="center">
<inline-formula id="inf248">
<mml:math id="m279">
<mml:mrow>
<mml:mn>4</mml:mn>
<mml:msub>
<mml:mi>T</mml:mi>
<mml:mrow>
<mml:mi>e</mml:mi>
<mml:mi>c</mml:mi>
<mml:mi>m</mml:mi>
</mml:mrow>
</mml:msub>
<mml:mo>&#x2b;</mml:mo>
<mml:mn>21</mml:mn>
<mml:msub>
<mml:mi>T</mml:mi>
<mml:mi>h</mml:mi>
</mml:msub>
</mml:mrow>
</mml:math>
</inline-formula>
</td>
</tr>
<tr>
<td align="left">[<xref ref-type="bibr" rid="B42">42</xref>]</td>
<td align="center">
<inline-formula id="inf249">
<mml:math id="m280">
<mml:mrow>
<mml:msub>
<mml:mi>T</mml:mi>
<mml:mrow>
<mml:mi>f</mml:mi>
<mml:mi>e</mml:mi>
</mml:mrow>
</mml:msub>
<mml:mo>&#x2b;</mml:mo>
<mml:mn>7</mml:mn>
<mml:msub>
<mml:mi>T</mml:mi>
<mml:mi>h</mml:mi>
</mml:msub>
<mml:mo>&#x2b;</mml:mo>
<mml:msub>
<mml:mi>T</mml:mi>
<mml:mrow>
<mml:mi>D</mml:mi>
<mml:mo>/</mml:mo>
<mml:mi>E</mml:mi>
</mml:mrow>
</mml:msub>
</mml:mrow>
</mml:math>
</inline-formula>
</td>
<td align="center">
<inline-formula id="inf250">
<mml:math id="m281">
<mml:mrow>
<mml:mn>8</mml:mn>
<mml:msub>
<mml:mi>T</mml:mi>
<mml:mi>h</mml:mi>
</mml:msub>
<mml:mo>&#x2b;</mml:mo>
<mml:msub>
<mml:mrow>
<mml:mn>2</mml:mn>
<mml:mi>T</mml:mi>
</mml:mrow>
<mml:mrow>
<mml:mi>D</mml:mi>
<mml:mo>/</mml:mo>
<mml:mi>E</mml:mi>
</mml:mrow>
</mml:msub>
</mml:mrow>
</mml:math>
</inline-formula>
</td>
<td align="center">
<inline-formula id="inf251">
<mml:math id="m282">
<mml:mrow>
<mml:mn>7</mml:mn>
<mml:msub>
<mml:mi>T</mml:mi>
<mml:mi>h</mml:mi>
</mml:msub>
<mml:mo>&#x2b;</mml:mo>
<mml:msub>
<mml:mi>T</mml:mi>
<mml:mrow>
<mml:mi>D</mml:mi>
<mml:mo>/</mml:mo>
<mml:mi>E</mml:mi>
</mml:mrow>
</mml:msub>
</mml:mrow>
</mml:math>
</inline-formula>
</td>
<td align="center">
<inline-formula id="inf252">
<mml:math id="m283">
<mml:mrow>
<mml:msub>
<mml:mi>T</mml:mi>
<mml:mrow>
<mml:mi>f</mml:mi>
<mml:mi>e</mml:mi>
</mml:mrow>
</mml:msub>
<mml:mo>&#x2b;</mml:mo>
<mml:mn>22</mml:mn>
<mml:msub>
<mml:mi>T</mml:mi>
<mml:mi>h</mml:mi>
</mml:msub>
<mml:mo>&#x2b;</mml:mo>
<mml:mn>5</mml:mn>
<mml:msub>
<mml:mi>T</mml:mi>
<mml:mrow>
<mml:mi>D</mml:mi>
<mml:mo>/</mml:mo>
<mml:mi>E</mml:mi>
</mml:mrow>
</mml:msub>
</mml:mrow>
</mml:math>
</inline-formula>
</td>
</tr>
<tr>
<td align="left">[<xref ref-type="bibr" rid="B43">43</xref>]</td>
<td align="center">
<inline-formula id="inf253">
<mml:math id="m284">
<mml:mrow>
<mml:msub>
<mml:mrow>
<mml:mn>2</mml:mn>
<mml:mi>T</mml:mi>
</mml:mrow>
<mml:mrow>
<mml:mi>e</mml:mi>
<mml:mi>c</mml:mi>
<mml:mi>m</mml:mi>
</mml:mrow>
</mml:msub>
<mml:mo>&#x2b;</mml:mo>
<mml:mn>9</mml:mn>
<mml:msub>
<mml:mi>T</mml:mi>
<mml:mi>h</mml:mi>
</mml:msub>
<mml:mo>&#x2b;</mml:mo>
<mml:msub>
<mml:mi>T</mml:mi>
<mml:mrow>
<mml:mi>f</mml:mi>
<mml:mi>e</mml:mi>
</mml:mrow>
</mml:msub>
</mml:mrow>
</mml:math>
</inline-formula>
</td>
<td align="center">
<inline-formula id="inf254">
<mml:math id="m285">
<mml:mrow>
<mml:mn>9</mml:mn>
<mml:msub>
<mml:mi>T</mml:mi>
<mml:mi>h</mml:mi>
</mml:msub>
<mml:mo>&#x2b;</mml:mo>
<mml:msub>
<mml:mi>T</mml:mi>
<mml:mrow>
<mml:mi>e</mml:mi>
<mml:mi>c</mml:mi>
<mml:mi>m</mml:mi>
</mml:mrow>
</mml:msub>
</mml:mrow>
</mml:math>
</inline-formula>
</td>
<td align="center">
<inline-formula id="inf255">
<mml:math id="m286">
<mml:mrow>
<mml:mn>4</mml:mn>
<mml:msub>
<mml:mi>T</mml:mi>
<mml:mi>h</mml:mi>
</mml:msub>
</mml:mrow>
</mml:math>
</inline-formula>
</td>
<td align="center">
<inline-formula id="inf256">
<mml:math id="m287">
<mml:mrow>
<mml:msub>
<mml:mrow>
<mml:mn>3</mml:mn>
<mml:mi>T</mml:mi>
</mml:mrow>
<mml:mrow>
<mml:mi>e</mml:mi>
<mml:mi>c</mml:mi>
<mml:mi>m</mml:mi>
</mml:mrow>
</mml:msub>
<mml:mo>&#x2b;</mml:mo>
<mml:mn>22</mml:mn>
<mml:msub>
<mml:mi>T</mml:mi>
<mml:mi>h</mml:mi>
</mml:msub>
<mml:mo>&#x2b;</mml:mo>
<mml:msub>
<mml:mi>T</mml:mi>
<mml:mrow>
<mml:mi>f</mml:mi>
<mml:mi>e</mml:mi>
</mml:mrow>
</mml:msub>
</mml:mrow>
</mml:math>
</inline-formula>
</td>
</tr>
<tr>
<td align="left">Proposed</td>
<td align="center">
<inline-formula id="inf257">
<mml:math id="m288">
<mml:mrow>
<mml:mn>3</mml:mn>
<mml:msub>
<mml:mi>T</mml:mi>
<mml:mrow>
<mml:mi>c</mml:mi>
<mml:mi>m</mml:mi>
</mml:mrow>
</mml:msub>
<mml:mo>&#x2b;</mml:mo>
<mml:mn>8</mml:mn>
<mml:msub>
<mml:mi>T</mml:mi>
<mml:mi>h</mml:mi>
</mml:msub>
</mml:mrow>
</mml:math>
</inline-formula>
</td>
<td align="center">
<inline-formula id="inf258">
<mml:math id="m289">
<mml:mrow>
<mml:mn>2</mml:mn>
<mml:msub>
<mml:mi>T</mml:mi>
<mml:mrow>
<mml:mi>c</mml:mi>
<mml:mi>m</mml:mi>
</mml:mrow>
</mml:msub>
<mml:mo>&#x2b;</mml:mo>
<mml:mn>7</mml:mn>
<mml:msub>
<mml:mi>T</mml:mi>
<mml:mi>h</mml:mi>
</mml:msub>
</mml:mrow>
</mml:math>
</inline-formula>
</td>
<td align="center">
<inline-formula id="inf259">
<mml:math id="m290">
<mml:mrow>
<mml:mn>3</mml:mn>
<mml:msub>
<mml:mi>T</mml:mi>
<mml:mrow>
<mml:mi>c</mml:mi>
<mml:mi>m</mml:mi>
</mml:mrow>
</mml:msub>
<mml:mo>&#x2b;</mml:mo>
<mml:mn>4</mml:mn>
<mml:msub>
<mml:mi>T</mml:mi>
<mml:mi>h</mml:mi>
</mml:msub>
</mml:mrow>
</mml:math>
</inline-formula>
</td>
<td align="center">
<inline-formula id="inf260">
<mml:math id="m291">
<mml:mrow>
<mml:mn>8</mml:mn>
<mml:msub>
<mml:mi>T</mml:mi>
<mml:mrow>
<mml:mi>c</mml:mi>
<mml:mi>m</mml:mi>
</mml:mrow>
</mml:msub>
<mml:mo>&#x2b;</mml:mo>
<mml:mn>19</mml:mn>
<mml:msub>
<mml:mi>T</mml:mi>
<mml:mi>h</mml:mi>
</mml:msub>
</mml:mrow>
</mml:math>
</inline-formula>
</td>
</tr>
</tbody>
</table>
</table-wrap>
<p>According to the proposed scheme, the time cost for user authentication is <inline-formula id="inf261">
<mml:math id="m292">
<mml:mrow>
<mml:mn>3</mml:mn>
<mml:msub>
<mml:mi>T</mml:mi>
<mml:mrow>
<mml:mi>c</mml:mi>
<mml:mi>m</mml:mi>
</mml:mrow>
</mml:msub>
<mml:mo>&#x2b;</mml:mo>
<mml:mn>8</mml:mn>
<mml:msub>
<mml:mi>T</mml:mi>
<mml:mi>h</mml:mi>
</mml:msub>
</mml:mrow>
</mml:math>
</inline-formula>, the time cost for TRC authentication is <inline-formula id="inf262">
<mml:math id="m293">
<mml:mrow>
<mml:mn>2</mml:mn>
<mml:msub>
<mml:mi>T</mml:mi>
<mml:mrow>
<mml:mi>c</mml:mi>
<mml:mi>m</mml:mi>
</mml:mrow>
</mml:msub>
<mml:mo>&#x2b;</mml:mo>
<mml:mn>7</mml:mn>
<mml:msub>
<mml:mi>T</mml:mi>
<mml:mi>h</mml:mi>
</mml:msub>
</mml:mrow>
</mml:math>
</inline-formula>, and the time cost for SC authentication is <inline-formula id="inf263">
<mml:math id="m294">
<mml:mrow>
<mml:mn>3</mml:mn>
<mml:msub>
<mml:mi>T</mml:mi>
<mml:mrow>
<mml:mi>c</mml:mi>
<mml:mi>m</mml:mi>
</mml:mrow>
</mml:msub>
<mml:mo>&#x2b;</mml:mo>
<mml:mn>4</mml:mn>
<mml:msub>
<mml:mi>T</mml:mi>
<mml:mi>h</mml:mi>
</mml:msub>
</mml:mrow>
</mml:math>
</inline-formula>. Therefore, the total time cost for the proposed scheme is <inline-formula id="inf264">
<mml:math id="m295">
<mml:mrow>
<mml:mn>8</mml:mn>
<mml:msub>
<mml:mi>T</mml:mi>
<mml:mrow>
<mml:mi>c</mml:mi>
<mml:mi>m</mml:mi>
</mml:mrow>
</mml:msub>
<mml:mo>&#x2b;</mml:mo>
<mml:mn>19</mml:mn>
<mml:msub>
<mml:mi>T</mml:mi>
<mml:mi>h</mml:mi>
</mml:msub>
</mml:mrow>
</mml:math>
</inline-formula>. In Chang [<xref ref-type="bibr" rid="B17">17</xref>], the time costs for the communication entities are <inline-formula id="inf265">
<mml:math id="m296">
<mml:mrow>
<mml:mn>2</mml:mn>
<mml:msub>
<mml:mi>T</mml:mi>
<mml:mrow>
<mml:mi>e</mml:mi>
<mml:mi>c</mml:mi>
<mml:mi>m</mml:mi>
</mml:mrow>
</mml:msub>
<mml:mo>&#x2b;</mml:mo>
<mml:mn>7</mml:mn>
<mml:msub>
<mml:mi>T</mml:mi>
<mml:mi>h</mml:mi>
</mml:msub>
</mml:mrow>
</mml:math>
</inline-formula>, <inline-formula id="inf266">
<mml:math id="m297">
<mml:mrow>
<mml:mn>9</mml:mn>
<mml:msub>
<mml:mi>T</mml:mi>
<mml:mi>h</mml:mi>
</mml:msub>
</mml:mrow>
</mml:math>
</inline-formula>, and <inline-formula id="inf267">
<mml:math id="m298">
<mml:mrow>
<mml:mn>2</mml:mn>
<mml:msub>
<mml:mi>T</mml:mi>
<mml:mrow>
<mml:mi>e</mml:mi>
<mml:mi>c</mml:mi>
<mml:mi>m</mml:mi>
</mml:mrow>
</mml:msub>
<mml:mo>&#x2b;</mml:mo>
<mml:mn>5</mml:mn>
<mml:msub>
<mml:mi>T</mml:mi>
<mml:mi>h</mml:mi>
</mml:msub>
</mml:mrow>
</mml:math>
</inline-formula> respectively. Thus, the total time cost is <inline-formula id="inf268">
<mml:math id="m299">
<mml:mrow>
<mml:mn>4</mml:mn>
<mml:msub>
<mml:mi>T</mml:mi>
<mml:mrow>
<mml:mi>e</mml:mi>
<mml:mi>c</mml:mi>
<mml:mi>m</mml:mi>
</mml:mrow>
</mml:msub>
<mml:mo>&#x2b;</mml:mo>
<mml:mn>21</mml:mn>
<mml:msub>
<mml:mi>T</mml:mi>
<mml:mi>h</mml:mi>
</mml:msub>
</mml:mrow>
</mml:math>
</inline-formula>. In Wazid [<xref ref-type="bibr" rid="B19">19</xref>], the time costs for the communication entities are <inline-formula id="inf269">
<mml:math id="m300">
<mml:mrow>
<mml:msub>
<mml:mi>T</mml:mi>
<mml:mrow>
<mml:mi>f</mml:mi>
<mml:mi>e</mml:mi>
</mml:mrow>
</mml:msub>
<mml:mo>&#x2b;</mml:mo>
<mml:mn>7</mml:mn>
<mml:msub>
<mml:mi>T</mml:mi>
<mml:mi>h</mml:mi>
</mml:msub>
<mml:mo>&#x2b;</mml:mo>
<mml:msub>
<mml:mi>T</mml:mi>
<mml:mrow>
<mml:mi>D</mml:mi>
<mml:mo>/</mml:mo>
<mml:mi>E</mml:mi>
</mml:mrow>
</mml:msub>
</mml:mrow>
</mml:math>
</inline-formula>, <inline-formula id="inf270">
<mml:math id="m301">
<mml:mrow>
<mml:mn>8</mml:mn>
<mml:msub>
<mml:mi>T</mml:mi>
<mml:mi>h</mml:mi>
</mml:msub>
<mml:mo>&#x2b;</mml:mo>
<mml:msub>
<mml:mrow>
<mml:mn>2</mml:mn>
<mml:mi>T</mml:mi>
</mml:mrow>
<mml:mrow>
<mml:mi>D</mml:mi>
<mml:mo>/</mml:mo>
<mml:mi>E</mml:mi>
</mml:mrow>
</mml:msub>
</mml:mrow>
</mml:math>
</inline-formula>, and <inline-formula id="inf271">
<mml:math id="m302">
<mml:mrow>
<mml:mn>7</mml:mn>
<mml:msub>
<mml:mi>T</mml:mi>
<mml:mi>h</mml:mi>
</mml:msub>
<mml:mo>&#x2b;</mml:mo>
<mml:msub>
<mml:mi>T</mml:mi>
<mml:mrow>
<mml:mi>D</mml:mi>
<mml:mo>/</mml:mo>
<mml:mi>E</mml:mi>
</mml:mrow>
</mml:msub>
</mml:mrow>
</mml:math>
</inline-formula> respectively. Thus, the total time cost is <inline-formula id="inf272">
<mml:math id="m303">
<mml:mrow>
<mml:msub>
<mml:mi>T</mml:mi>
<mml:mrow>
<mml:mi>f</mml:mi>
<mml:mi>e</mml:mi>
</mml:mrow>
</mml:msub>
<mml:mo>&#x2b;</mml:mo>
<mml:mn>22</mml:mn>
<mml:msub>
<mml:mi>T</mml:mi>
<mml:mi>h</mml:mi>
</mml:msub>
<mml:mo>&#x2b;</mml:mo>
<mml:mn>5</mml:mn>
<mml:msub>
<mml:mi>T</mml:mi>
<mml:mrow>
<mml:mi>D</mml:mi>
<mml:mo>/</mml:mo>
<mml:mi>E</mml:mi>
</mml:mrow>
</mml:msub>
</mml:mrow>
</mml:math>
</inline-formula>. In Li [<xref ref-type="bibr" rid="B18">18</xref>], the time costs for the communication entities are <inline-formula id="inf273">
<mml:math id="m304">
<mml:mrow>
<mml:msub>
<mml:mrow>
<mml:mn>2</mml:mn>
<mml:mi>T</mml:mi>
</mml:mrow>
<mml:mrow>
<mml:mi>e</mml:mi>
<mml:mi>c</mml:mi>
<mml:mi>m</mml:mi>
</mml:mrow>
</mml:msub>
<mml:mo>&#x2b;</mml:mo>
<mml:mn>9</mml:mn>
<mml:msub>
<mml:mi>T</mml:mi>
<mml:mi>h</mml:mi>
</mml:msub>
<mml:mo>&#x2b;</mml:mo>
<mml:msub>
<mml:mi>T</mml:mi>
<mml:mrow>
<mml:mi>f</mml:mi>
<mml:mi>e</mml:mi>
</mml:mrow>
</mml:msub>
</mml:mrow>
</mml:math>
</inline-formula>, <inline-formula id="inf274">
<mml:math id="m305">
<mml:mrow>
<mml:mn>9</mml:mn>
<mml:msub>
<mml:mi>T</mml:mi>
<mml:mi>h</mml:mi>
</mml:msub>
<mml:mo>&#x2b;</mml:mo>
<mml:msub>
<mml:mi>T</mml:mi>
<mml:mrow>
<mml:mi>e</mml:mi>
<mml:mi>c</mml:mi>
<mml:mi>m</mml:mi>
</mml:mrow>
</mml:msub>
</mml:mrow>
</mml:math>
</inline-formula>, and <inline-formula id="inf275">
<mml:math id="m306">
<mml:mrow>
<mml:mn>4</mml:mn>
<mml:msub>
<mml:mi>T</mml:mi>
<mml:mi>h</mml:mi>
</mml:msub>
</mml:mrow>
</mml:math>
</inline-formula> respectively. Thus, the total time cost is <inline-formula id="inf276">
<mml:math id="m307">
<mml:mrow>
<mml:msub>
<mml:mrow>
<mml:mn>3</mml:mn>
<mml:mi>T</mml:mi>
</mml:mrow>
<mml:mrow>
<mml:mi>e</mml:mi>
<mml:mi>c</mml:mi>
<mml:mi>m</mml:mi>
</mml:mrow>
</mml:msub>
<mml:mo>&#x2b;</mml:mo>
<mml:mn>22</mml:mn>
<mml:msub>
<mml:mi>T</mml:mi>
<mml:mi>h</mml:mi>
</mml:msub>
<mml:mo>&#x2b;</mml:mo>
<mml:msub>
<mml:mi>T</mml:mi>
<mml:mrow>
<mml:mi>f</mml:mi>
<mml:mi>e</mml:mi>
</mml:mrow>
</mml:msub>
</mml:mrow>
</mml:math>
</inline-formula>. Compared to the schemes by Chang [<xref ref-type="bibr" rid="B17">17</xref>] and Li [<xref ref-type="bibr" rid="B18">18</xref>], the proposed scheme has lower computational overhead. Although the proposed scheme requires more computational overhead than Wazid [<xref ref-type="bibr" rid="B19">19</xref>], it provides more security features. <xref ref-type="fig" rid="F5">Figures 5</xref>&#x2013;<xref ref-type="fig" rid="F8">8</xref> show the computational overhead for each scheme across different communication entities. As the number of user devices increases, the proposed solution becomes more acceptable.</p>
<fig id="F5" position="float">
<label>FIGURE 5</label>
<caption>
<p>Computation overhead of user.</p>
</caption>
<graphic xlink:href="fphy-13-1522170-g005.tif"/>
</fig>
<fig id="F6" position="float">
<label>FIGURE 6</label>
<caption>
<p>Computation overhead of TRC.</p>
</caption>
<graphic xlink:href="fphy-13-1522170-g006.tif"/>
</fig>
<fig id="F7" position="float">
<label>FIGURE 7</label>
<caption>
<p>Computation overhead of SC.</p>
</caption>
<graphic xlink:href="fphy-13-1522170-g007.tif"/>
</fig>
<fig id="F8" position="float">
<label>FIGURE 8</label>
<caption>
<p>Computation overhead.</p>
</caption>
<graphic xlink:href="fphy-13-1522170-g008.tif"/>
</fig>
</sec>
<sec id="s7-2">
<title>6.2 Communication overhead comparison</title>
<p>The communication overhead is shown in <xref ref-type="table" rid="T3">Table 3</xref>. The proposed scheme uses a 160-bit chebyshev chaotic map, a 160-bit random number, a 160-bit identity identifier, 128-bit symmetric encryption/decryption, 160-bit hash value, and a 32-bit timestamp. The three messages transmitted in this scheme are <inline-formula id="inf277">
<mml:math id="m308">
<mml:mrow>
<mml:mfenced open="{" close="}" separators="|">
<mml:mrow>
<mml:msub>
<mml:mi>V</mml:mi>
<mml:mn>1</mml:mn>
</mml:msub>
<mml:mo>,</mml:mo>
<mml:msub>
<mml:mi>V</mml:mi>
<mml:mn>3</mml:mn>
</mml:msub>
<mml:mo>,</mml:mo>
<mml:msub>
<mml:mi>V</mml:mi>
<mml:mn>4</mml:mn>
</mml:msub>
<mml:mo>,</mml:mo>
<mml:msub>
<mml:mi>V</mml:mi>
<mml:mn>5</mml:mn>
</mml:msub>
<mml:mo>,</mml:mo>
<mml:msub>
<mml:mi>V</mml:mi>
<mml:mn>6</mml:mn>
</mml:msub>
<mml:mo>,</mml:mo>
<mml:msub>
<mml:mi>T</mml:mi>
<mml:mn>1</mml:mn>
</mml:msub>
</mml:mrow>
</mml:mfenced>
</mml:mrow>
</mml:math>
</inline-formula>, <inline-formula id="inf278">
<mml:math id="m309">
<mml:mrow>
<mml:mfenced open="{" close="}" separators="|">
<mml:mrow>
<mml:msub>
<mml:mrow>
<mml:msub>
<mml:mrow>
<mml:mi>S</mml:mi>
<mml:mi>I</mml:mi>
<mml:mi>D</mml:mi>
<mml:mo>&#x2a;</mml:mo>
</mml:mrow>
<mml:mi>j</mml:mi>
</mml:msub>
<mml:mo>,</mml:mo>
<mml:mi>V</mml:mi>
</mml:mrow>
<mml:mn>1</mml:mn>
</mml:msub>
<mml:mo>,</mml:mo>
<mml:msub>
<mml:mi>V</mml:mi>
<mml:mn>7</mml:mn>
</mml:msub>
<mml:mo>,</mml:mo>
<mml:msub>
<mml:mi>V</mml:mi>
<mml:mn>8</mml:mn>
</mml:msub>
<mml:mo>,</mml:mo>
<mml:msub>
<mml:mi>V</mml:mi>
<mml:mn>9</mml:mn>
</mml:msub>
<mml:mo>,</mml:mo>
<mml:msub>
<mml:mi>T</mml:mi>
<mml:mn>1</mml:mn>
</mml:msub>
</mml:mrow>
</mml:mfenced>
</mml:mrow>
</mml:math>
</inline-formula>, and <inline-formula id="inf279">
<mml:math id="m310">
<mml:mrow>
<mml:mfenced open="{" close="}" separators="|">
<mml:mrow>
<mml:msub>
<mml:mi>V</mml:mi>
<mml:mn>10</mml:mn>
</mml:msub>
<mml:mo>,</mml:mo>
<mml:msub>
<mml:mi>V</mml:mi>
<mml:mn>12</mml:mn>
</mml:msub>
<mml:mo>,</mml:mo>
<mml:msub>
<mml:mi>T</mml:mi>
<mml:mn>3</mml:mn>
</mml:msub>
</mml:mrow>
</mml:mfenced>
</mml:mrow>
</mml:math>
</inline-formula>. The bit consumption for these three messages is 832 bits, 832 bits, and 352 bits, respectively, resulting in a total communication overhead of 2016 bits. In Chang [<xref ref-type="bibr" rid="B17">17</xref>], the communication costs for each entity are 672 bits, 512 bits, and 1,088 bits, respectively, with a total communication overhead of 2,272 bits. In Wazid [<xref ref-type="bibr" rid="B42">42</xref>], the communication costs for each entity are 512, 1,088, and 384 bits, respectively, resulting in a total communication overhead of 1984 bits. In Li [<xref ref-type="bibr" rid="B18">18</xref>], the communication costs for each entity are 1,120, 1,120, and 320 bits, respectively, with a total communication overhead of 2,560 bits. Wazid [<xref ref-type="bibr" rid="B42">42</xref>]</p>
<table-wrap id="T3" position="float">
<label>TABLE 3</label>
<caption>
<p>Communication overhead.</p>
</caption>
<table>
<thead valign="top">
<tr>
<th align="center">Scheme</th>
<th align="center">User</th>
<th align="center">TRC</th>
<th align="center">SC</th>
<th align="center">Total</th>
</tr>
</thead>
<tbody valign="top">
<tr>
<td align="center">[<xref ref-type="bibr" rid="B41">41</xref>]</td>
<td align="center">672</td>
<td align="center">512</td>
<td align="center">1,088</td>
<td align="center">2,272</td>
</tr>
<tr>
<td align="center">[<xref ref-type="bibr" rid="B42">42</xref>]</td>
<td align="center">512</td>
<td align="center">1,088</td>
<td align="center">384</td>
<td align="center">1984</td>
</tr>
<tr>
<td align="center">[<xref ref-type="bibr" rid="B43">43</xref>]</td>
<td align="center">1,120</td>
<td align="center">1,120</td>
<td align="center">320</td>
<td align="center">2,560</td>
</tr>
<tr>
<td align="center">Ours</td>
<td align="center">832</td>
<td align="center">832</td>
<td align="center">352</td>
<td align="center">2016</td>
</tr>
</tbody>
</table>
</table-wrap>
<p>While meeting more security performance and resistance to attacks, the communication overhead for some nodes in this scheme is slightly higher than that of other nodes. First, Chang [<xref ref-type="bibr" rid="B41">41</xref>] and Wazid [<xref ref-type="bibr" rid="B42">42</xref>]do not support resistance to password guessing attacks, so the user&#x2019;s communication overhead is slightly lower than that of the proposed scheme. In order to implement this function, this consumes more communication overhead. Additionally, the proposed scheme has slightly higher communication overhead than Wazid [<xref ref-type="bibr" rid="B42">42</xref>]. However, Chang [<xref ref-type="bibr" rid="B41">41</xref>] does not support the safety requirement. <xref ref-type="fig" rid="F9">Figures 9</xref>&#x2013;<xref ref-type="fig" rid="F12">12</xref> visually illustrate the communication consumption of each scheme on different entities. Compared to other schemes, the communication overhead is lower. Therefore, the scheme in this article meets the practical needs of electronic evidence interaction in IoT.</p>
<fig id="F9" position="float">
<label>FIGURE 9</label>
<caption>
<p>Communication overhead of user.</p>
</caption>
<graphic xlink:href="fphy-13-1522170-g009.tif"/>
</fig>
<fig id="F10" position="float">
<label>FIGURE 10</label>
<caption>
<p>Communication overhead of TRC.</p>
</caption>
<graphic xlink:href="fphy-13-1522170-g010.tif"/>
</fig>
<fig id="F11" position="float">
<label>FIGURE 11</label>
<caption>
<p>Communication overhead of SC.</p>
</caption>
<graphic xlink:href="fphy-13-1522170-g011.tif"/>
</fig>
<fig id="F12" position="float">
<label>FIGURE 12</label>
<caption>
<p>Communication overhead.</p>
</caption>
<graphic xlink:href="fphy-13-1522170-g012.tif"/>
</fig>
</sec>
</sec>
<sec sec-type="conclusion" id="s8">
<title>7 Conclusion</title>
<p>This paper provides an in-depth analysis of the security and privacy issues surrounding electronic evidence in IoT. It highlights that the importance of electronic evidence in the judicial field is increasing, but its inherent vulnerabilities also pose significant privacy risks. To address this issue, this paper proposes a secure interaction scheme for electronic evidence in IoT. This scheme innovatively combines chebyshev chaotic map, hash functions and XOR operations to ensure the security of the electronic evidence transmission process. The scheme was then subjected to a security analysis using the random oracle model and the Scyther, proving its resilience against various types of attacks. Furthermore, the security analysis and performance experiment results demonstrate that the scheme optimizes authentication efficiency while ensuring security. This research not only offers new insights and methods for the secure management of electronic evidence in IoT environments but also makes a positive contribution to the healthy development of IoT technology, the maintenance of judicial fairness, and the protection of personal privacy. In the practical application, with numerous IoT devices and frequent data exchange, security risks also increase. The secure interaction scheme proposed in this paper can be applied to IoT security monitoring and management systems, achieving comprehensive monitoring and protection of device identity, data transmission, and storage processes, thereby improving the overall security of IoT systems.</p>
</sec>
</body>
<back>
<sec sec-type="data-availability" id="s9">
<title>Data availability statement</title>
<p>The original contributions presented in the study are included in the article/supplementary material, further inquiries can be directed to the corresponding author.</p>
</sec>
<sec sec-type="author-contributions" id="s10">
<title>Author contributions</title>
<p>YX: Conceptualization, Data curation, Formal Analysis, Investigation, Methodology, Project administration, Software, Supervision, Writing&#x2013;original draft, Writing&#x2013;review and editing. LC: Formal Analysis, Investigation, Methodology, Resources, Validation, Visualization, Writing&#x2013;review and editing.</p>
</sec>
<sec sec-type="funding-information" id="s11">
<title>Funding</title>
<p>The author(s) declare that financial support was received for the research, authorship, and/or publication of this article. The authors acknowledge funding received from the following science foundations: Research on the basic theory and methodology of data investigation (2023JKF01SK08).</p>
</sec>
<sec sec-type="COI-statement" id="s12">
<title>Conflict of interest</title>
<p>The authors declare that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest.</p>
</sec>
<sec sec-type="ai-statement" id="s13">
<title>Generative AI statement</title>
<p>The author(s) declare that no Generative AI was used in the creation of this manuscript.</p>
</sec>
<sec sec-type="disclaimer" id="s14">
<title>Publisher&#x2019;s note</title>
<p>All claims expressed in this article are solely those of the authors and do not necessarily represent those of their affiliated organizations, or those of the publisher, the editors and the reviewers. Any product that may be evaluated in this article, or claim that may be made by its manufacturer, is not guaranteed or endorsed by the publisher.</p>
</sec>
<ref-list>
<title>References</title>
<ref id="B1">
<label>1.</label>
<citation citation-type="journal">
<person-group person-group-type="author">
<name>
<surname>Nassereddine</surname>
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