Group Signature

Ring signatures, first introduced by Rivest, Shamir, and Tauman, enable a user to sign a message so that a ring of possible signers (of which the user is a member) is identified, without revealing exactly which member of that ring actually generated the signature. In contrast to group signatures, ring signatures are completely "ad-hoc" and do not require any central authority or coordination among the various users (indeed, users do not even need to be aware of each other); furthermore, ring signature schemes grant users fine-grained control over the level of anonymity associated with any particular signature. This paper has two main areas of focus. First, we examine previous definitions of security for ring signature schemes and suggest that most of these prior definitions are too weak, in the sense that they do not take into account certain realistic attacks. We propose new definitions of anonymity and unforgeability which address these threats, and give separation results proving that our new notions are strictly stronger than previous ones. Second, we show the first constructions of ring signature schemes in the standard model. One scheme is based on generic assumptions and satisfies our strongest definitions of security. Two additional schemes are more efficient, but achieve weaker security guarantees and more limited functionality.

html. 2 equensWorldline depuis 2016. 3 Présentation commerciale . 1. Génération des Clés : KeyGen Clé secrète sk = (G, S, P ) H matrice de parité de C[n, k, d] avec D un algorithme de décodage. S une matrice binaire inversible (n -k) × (n -k). P une matrice binaire de permutation n × n. Clé publique pk pk = (H = SHP, t = d-1 2 ) 2. Chiffrement : Enc(pk, m). m ∈ {0, 1} n tel que ωt(m) = t. c = H m . 3. Déchiffrement : Dec(sk, c). Calculer S -1 c = HP m . Puisque ωt(P m ) t, D permet de retrouver P m . Retourner m = P -1 P m .

Les croissances constantes de l’Internet et des services associés ont conduit à des problématiques naturellement liées au domaine de la cryptographie, parmi lesquelles l’authentification et le respect de la vie privée des utilisateurs. L’utilisation désormais commune d’appareils connectés (smartphone, tablette, montre, …) comme moyen d’authentification amène à considérer la génération et/ou la gestion de clés cryptographiques par de tels appareils pour répondre à ces besoins. Les résonances cryptographiques identifiées de ces deux cas d’étude sont respectivement le domaine des Fuzzy Extractors (« Extracteurs de Flous » en français) et les schémas de signature de groupe. D’une part, cette thèse présente alors le premier Fuzzy Extractror non basé sur la distance de Hamming à être réutilisable (dans le modèle de l’oracle aléatoire non programmable). Ce faisant, nous avons alors pu concevoir un module de génération de clés cryptographiques permettant d'authentifier un utilisateur à ...

In this work we propose the first code-based group signature. As it will be described below, its security is based on a relaxation of the model of Bellare, Shi and Zhang [3] (BSZ model) verifying the properties of anonymity, traceability and non-frameability. Furthermore, it has numerous advantages over all existing post-quantum constructions and even competes (in terms of properties) with pairing based constructions: it allows to dynamically add new members and signature and public key sizes are constant with respect to the number of group members. Last but not least, our scheme can be extended into a traceable signature according to the definition of Kiayias, Tsiounis and Yung [19] (KTY model) and handles membership revocation. The main idea of our scheme consists in building a collision of two syndromes associated to two different matrices: a random one which enables to build a random syndrome from a chosen small weight vector; and a trapdoor matrix for the syndrome decoding problem, which permits to find a small weight preimage of the previous random syndrome. These two small weight vectors will constitute the group member's secret signing key whose knowledge will be proved thanks to a variation of Stern's authentication protocol. For applications, we consider the case of the code-based CFS signature scheme of Courtois, Finiasz and Sendrier. 3 cases: c = 0: P sends π, u c = 1: P sends π, z + u c = 2: P sends π(z), π(u) 5. 3 cases: c = 0: V checks c 1 , c 2 c = 1: V checks c 1 , c 3 c = 2: V checks c 2 , c 3 and ωt(π(z)) = ω 6. V outputs Accept if all checks passed ⊥ otherwise.

We propose a short traceable signature scheme based on bilinear pairings. Traceable signatures, introduced by Kiayias, Tsiounis and Yung (KTY), support an extended set of fairness mechanisms (mechanisms for anonymity management and revocation) when compared with the traditional group signatures. Designing short signatures based on the power of pairing has been a current activity of cryptographic research, and is especially needed for long constructions like that of traceable signatures. The size of a signature in our scheme is less than one third of the size in the KTY scheme and about 40% of the size of the pairing based traceable signature (which has been the shortest till today). The security of our scheme is based on the Strong Diffie-Hellman assumption and the Decision Linear Diffie-Hellman assumption. We prove the security of our system in random oracle model using the security model given by KTY.

Efficient member revocation and strong security against attacks are prominent requirements in group signature schemes. Among the revocation approaches Verifier-local revocation is the most flexible and efficient method since it requires to inform only the verifiers regarding the revoked members. The verifier-local revocation technique uses a token system to manage members’ status. However, the existing group signature schemes with verifier-local revocability rely on weaker security. On the other hand, existing static group signature schemes rely on a stronger security notion called, full-anonymity. Achieving the full-anonymity for group signature schemes with verifier-local revocation is a quite challenging task. This paper aims to obtain stronger security for the lattice-based group signature schemes with verifier-local revocability, which is closer to the full-anonymity. Moreover, this paper delivers a new key-generation method which outputs revocation tokens without derivin...

A group signature scheme allows group members to issue signatures on behalf of the group, while hiding for each signature which group member actually issued it. Such scheme also involves a group manager, who is able to open any group signature by showing which group member issued it. We introduce the concept of list signatures as a variant of group signatures which sets a limit on the number of signatures each group member may issue. These limits must be enforced without having the group manager open signatures of honest group members-which excludes the trivial solution in which the group manager opens every signature to see whether some group members exceed their limits. Furthermore, we consider the problem of publicly identifying group members who exceed their limits, also without involving the group manager.

Now a day’s people are using their smart phones for various purposes like uploading data, sharing data, use of online services, etc. along with their primary functions. But the problem with smart phones is that they are having limited computational and storage resources. Use of cloud computing in a mobile computing environment solves this problem which also increases the capacity of mobile devices. But the major concern about the use of cloud is the security issue which also becomes the problem in the mobile cloud computing environment. We proposed a light-weighted cryptographic mechanism a proxy re-encryption to solve the data integrity, data security issues in which users have to keep only short secret keys for all cryptographic operations in the mobile cloud without the involvement of any trusted third party. Group information sharing in cloud environments has become a boiling topic in modern decades. With the recognition of cloud computing, the way to reach secure associated eco...

Vehicular Ad-Hoc Network, better known as VANET is a promising new technology which combines the capabilities of different wireless networks in vehicles enabling Intelligent Transportation System (ITS). Vehicular Ad-Hoc networks provide communication between on-board unit (OBU) already integrated in the vehicles and road-side units (RSUs) consisting of on-board sensors, processing modules, and wireless communication modules. Immense amount of research is going on both by industry and academia. In vehicular communication because of the high speed of vehicles frequent handovers occur and hence there is always a requirement of secure and fast authentication for a seamless handover to take place. In this paper we propose an authentication scheme that will not only provide security and privacy but also will reduce the storage and communication overhead increasing the efficiency.

Multisignature threshold schemes combine the properties of threshold group-oriented signature schemes and Multisignature schemes to yield a signature scheme that allows more group members to collaboratively sign an arbitrary message. In contrast to threshold group signatures, the individual signers do not remain anonymous, but are publicly identifiable from the information contained in the valid Multisignature. The main objective of our project is to propose such a secure and efficient Multisignature scheme. Our project shows that the proposed scheme eliminates the latest attacks to which other similar schemes are subject. Multisignature is based on distributed-key management infrastructure (DKMI), which consists of distributed-key generation (DKG) protocol and distributed-key redistribution/updating (DKRU) protocol. The round optimal DKRU protocol solves a major problem with existing secret redistribution /updating schemes by giving group members a mechanism to identify malicious o...

Verifiable encryption is a primitive that can be used to build extremely efficient fair exchange protocols where the items exchanged represent digital signatures. Such protocols may be used to digitally sign contracts on the Internet. This paper presents an efficient protocol for verifiable encryption of digital signatures that improves the security and efficiency of the verifiable encryption scheme of Ateniese. Our protocol can be applied to group signatures, key escrow and publicly verifiable secret and signature sharing to prove the fairness.

Verifiable encryption is a primitive that can be used to build extremely efficient fair exchange protocols where the items exchanged represent digital signatures. Such protocols may be used to digitally sign contracts on the Internet. This paper presents an efficient protocol for verifiable encryption of digital signatures that improves the security and efficiency of the verifiable encryption scheme of Ateniese. Our protocol can be applied to group signatures, key escrow and publicly verifiable secret and signature sharing to prove the fairness.

One important requirement of electronic cash systems is the anonymity of customers. Unconditional anonymity is also very well suited to support criminals in blackmailing. Maitland and Boyd proposed at ICICS 2001 an offline electronic cash system based on a group signature scheme. Their scheme cannot be used to solve blackmailing and other anonymity problems such as money laundering and illegal purchases. Chen, Zhang and Wang suggested an offline electronic cash scheme to prevent blackmailing by using the group blind signature. In their payment system, they used a group signature scheme of Camenisch and Stadler for large groups which is not secure. In this paper we improve these electronic cash systems to prevent blackmailing, money laundering and illegal purchases by using a secure coalition-resistant group blind signature scheme.

A group signature scheme allows any group member to sign on behalf of the group in an anonymous and unlinkable fashion. In the event of a dispute, a designated trusted entity can reveal the identity of the signer. In this paper we propose a revocation method for group signatures based on the group signature scheme from . This method requires no time periods and offers constant length signatures.

on which the proxy signer can sign. Also, proxy signature schemes can be classified as proxy-unprotected and proxy-protected schemes. In an proxy-protected scheme, the original signer cannot forge a proxy signature in the name of the proxy signer. The proxyprotected schemes provide more security level than the proxy-unprotected signature schemes. A lot of proxy signature schemes [6], [7] and some ID-based proxy signature schemes with special features were proposed, such as identity-based multi-proxy signature [8], [9], identity-based strong designated verifier proxy signature [10], [11]. Cao and Cao [9] claimed that their scheme is provably secure in the random oracle model. However, Xiong et al. [12] proved that their scheme is not secure under their security model. The first proxy signature scheme based on the factoring integer problem is proposed by Shao [13], in 2003. Recently, Zhou et al. [14] proposed two efficient proxy protected signature schemes. Their first scheme is based on RSA [15] assumption and the second scheme is based on the integer factorization problem. Zhou et al. [14] claim that their schemes are more efficient than other schemes. However, Park et al. [16] point out their schemes are insecure. Moreover, Liu et al. [17] point out that Zhou et al.'s [14] schemes are vulnerable to the undelegated proxy signature attack: any attacker without the delegation of the original signer can generate a valid proxy signature. Xue et al. [18] proposed two proxy signature schemes based on the difficulty of factorings of large integers without formal security proofs. Recently, Shao [19] proposed proxy protected signature scheme based on RSA. Also, most proxy signature schemes are based on the difficulty of discrete logarithm problem [20] or elliptic curve discrete logarithm problem [21]. Chen et al. proposed in [20] a proxy signature scheme based on the Digital Signature Algorithm (DSA). Mambo et al. [1], [22] proposed three proxy signature schemes based on ElGamal's signature scheme [23], Schnorr's signature

A blind signature is a form of digital signature in which the content of a message is blinded before it is signed. The first blind digital signature scheme was proposed by Chaum in 1982. Chaum constructed the blind signatures as a key tool for developing anonymous electronic cash system. In this paper we propose two blind signature schemes and an elliptic curve version of Shao's signature scheme. Our schemes are based on the difficulty of solving the elliptic curve discrete logarithm problem.

One important property of group signatures is forward-security, which prevents an attacker in possession of a group signing key to forge signatures produced in the past. In case of exposure of one group member's signing key, group signatures lacking forward-security need to invalidate all group public and secret keys (by re-initializing the whole system) but also invalidate all previously issued group signatures. Most of the existing forward-secure group signatures (FS-GS) are built from number-theoretic security assumptions which are vulnerable to quantum computers. The only post-quantum secure FS-GS scheme is built from lattices by Ling et al. (PQCrypto 19) in the random oracle model, following the classical framework of encrypt-then-prove, thus using noninteractive zero-knowledge (NIZK) proofs. In this work, we achieve the first FS-GS from lattices in the standard model. Our starting point is the group signature of Katsumada and Yamada (Eurocrypt 19) which replaces NIZK by attribute-based signatures (ABS), thus removing the need for random oracles. We first modify the underlying ABS of Tsabary (TCC 17) to equip it with forward-security property. We then prove that by plugging it back in the group signature framework of Katsumada and Yamada (Eurocrypt 19), we can design a FS-GS scheme secure in the standard model with public key and signature size constant in the number of users. Our constant size is achieved by relying on complexity leveraging, which further implies relying on the subexponential hardness of the Short Integers Solution (SIS) assumption.

In this paper we construct a practical group blind signature scheme. Our scheme combines the already existing notions of blind signatures and group signatures. It is an extension of Camenisch and Stadler's Group Signature Scheme [5] that adds the blindness property. We show how to use our group blind signatures to construct an electronic cash system in which multiple banks can securely distribute anonymous and untraceable e-cash. Moreover, the identity of the e-cash issuing bank is concealed, which is conceptually novel. The space, time, and communication complexities of the relevant parameters and operations are independent of the group size.

In this paper we construct a practical group blind signature scheme. Our scheme combines the already existing notions of blind signatures and group signatures. It is an extension of Camenisch and Stadler's Group Signature Scheme [5] that adds the blindness property. We show how to use our group blind signatures to construct an electronic cash system in which multiple banks can securely distribute anonymous and untraceable e-cash. Moreover, the identity of the e-cash issuing bank is concealed, which is conceptually novel. The space, time, and communication complexities of the relevant parameters and operations are independent of the group size.

Direct Anonymous Attestation (DAA) is an anonymous digital signature that aims to provide both signer authentication and privacy. DAA was designed for the attestation service of the Trusted Platform Module (TPM). In this application, a DAA signer role is divided into two parts: the principal signer which is a TPM, and an assistant signer which is a standard computing platform in which the TPM is embedded, called the Host. A design feature of a DAA solution is to make the TPM workload as low as possible. This paper presents a lattice-based DAA (L-DAA) scheme to meet this requirement. Security of this scheme is proved in the Universally Composable (UC) security model under the hard assumptions of the Ring Inhomogeneous Short Integer Solution (Ring-ISIS) and Ring Learning With Errors (Ring-LWE) problems. Our L-DAA scheme includes two building blocks, one is a modification of the Boyen lattice based signature scheme and another is a modification of the Baum et al. lattice based commitme...

Two provably secure group identification schemes are presented in this report: 1) we extend De Santis, Crescenzo and Persiano's (SCP) anonymous group identification scheme to the discrete logarithm based case; then we provide a 3-move anonymous group identification scheme, which is more efficient than that presented in [SCPM, CDS], with the help of this basic scheme; 2) we also extend the original De Santis, Crescenzo and Persiano anonymous group identification scheme to the general case where each user holds public key which is chosen by herself independently. The communication cost for one round execution of the protocol is 2mk, where k is bit length of public key n and m is the number of users in the group.

This paper proposes a group key distribution scheme using smart contract-based blockchain technology. The smart contract's functions allow for securely distributing the group session key, following the initial legitimacy detection using public key infrastructure-based authentication. For message authentication, we propose a lightweight symmetric key cryptographybased group signature method, supporting the security and privacy requirements of vehicular ad hoc networks (VANETs). Our discussion examined the scheme's robustness against typical adversarial attacks. To evaluate the gas costs associated with smart contract's functions, we implemented it on the Ethereum main network. Finally, comprehensive analyses of computation and communication costs demonstrate the scheme's effectiveness.

A vehicular ad hoc network is a capable method of making possible road well-being, traffic supervision, as well as information distribution for driving users and travelers. One definitive objective in the blueprint of this type of network is to refuse to accept a variety of malevolent mistreatment and security assaults. The paper analyzed the existing procedure, which has covered the ways of offering security duties and conserving user solitude in the context of wireless access in vehicular environments (WAVE) applications. To make the standards more realistic, it considers techniques of certificate revocation and conditional privacy preservation. These techniques are found to be the most promising ones in vehicular ad hoc networks (VANET). Therefore, a group of narrative security methods is proposed for the safe implementation of the techniques of certificate revocation and conditional privacy preservation. For enhancement of security, the paper proposes that the message should be encapsulated with a proper certificate and be duly signed. For faster communication, we propose the use of optical wireless communication (OWC) between an onboard unit (OBU) and a roadside unit (RSU).

A Zero-knowledge protocol provides provably secure entity authentication based on a hard computational problem. Among many schemes proposed since 1984, the most practical rely on factoring and discrete log, but still they are practical schemes based on NP-hard problems. Among them, the problem SD of decoding linear codes is in spite of some 30 years of research effort, still exponential. We study a more general problem called MinRank that generalizes SD and contains also other well known hard problems. MinRank is also used in cryptanalysis of several public key cryptosystems such as birational schemes (Crypto'93), HFE (Crypto'99), GPT cryptosystem (Eurocrypt'91), TTM (Asiacrypt'2000) and Chen's authentication scheme (1996). We propose a new Zero-knowledge scheme based on MinRank. We prove it to be Zero-knowledge by black-box simulation. An adversary able to fraud for a given MinRank instance is either able to solve it, or is able to compute a collision on a given hash function. MinRank is one of the most efficient schemes based on NP-complete problems. It can be used to prove in Zero-knowledge a solution to any problem described by multivariate equations. We also present a version with a public key shared by a few users, that allows anonymous group signatures (a.k.a. ring signatures).

Acoustic territorial displays are common among birds but comparatively rare among mammals. An exceptionally vocal mammal well-known for its elaborate territorial displays is the polygynous greater sac-winged bat, Saccopteryx bilineata. Male S. bilineata are often philopatric and establish small territories in their birth colony in which females can roost during the day. During territorial defense, males produce complex territorial songs that are learned through vocal imitation. Territorial songs are mainly produced at dawn and dusk. We studied social influences on male vocal activity and the occurrence of vocal signatures in territorial songs of 27 male S. bilineata from 12 differentsized colonies in Panama. Males produced significantly more territorial songs when they had more territorial neighbors or when they had females roosting in their territories, indicating that male vocal activity rises with increasing male-male competition. Territorial songs are multisyllabic vocalizations with low-frequency buzz syllables being most prominent. We found statistical evidence for a pronounced individual signature encoded in the buzz syllables of territorial songs that could facilitate individual recognition among rival neighbors. Additionally, we found a vocal group signature in territorial songs, suggesting that young males may learn territorial songs from more than one tutor male. Resident male S. bilineata appear to cooperatively defend their colony against male intruders, making a group signature in territorial songs potentially advantageous.

In this paper, we introduce Attribute-Based Signatures with User-Controlled Linkability (ABS-UCL). Attribute-based signatures allow a signer who has enough credentials/attributes to anonymously sign a message w.r.t. some public policy revealing neither the attributes used nor his identity. User-controlled linkability is a new feature which allows a user to make some of his signatures directed at the same recipient linkable while still retaining anonymity. Such a feature is useful for many reallife applications. We give a general framework for constructing ABS-UCL and present an efficient instantiation of the construction that supports multiple attribute authorities.

For the proper performance of Vehicular Ad-hoc NETworks (VANETs) it is essential to protect the service against malicious nodes aiming at disrupting the proper operation by injecting fake, invalid data into the network. It is common to define a traditional identity-based authentication for vehicles, which are loaded with individual credentials. However, the use of these credentials in VANETs may allow vehicle tracking and thus violate users' privacy, a risk that can be overcome by means of anonymity schemes. This comes at the expenses, however, of on the one hand preventing VANET authorities from identifying malicious users and revoking them from the network, or on the other hand to avoid anonymity of users in front of the CA thus to allow their revocation. In this work, we describe a novel revocation scheme that is able to track and revoke specific users only after a number of complaints have been received while otherwise guaranteeing vehicle's anonymity.

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Vehicular adhoc network is one of the recent area of research to administer safety to human lives, controlling of messages and in disposal of messages to users and passengers. VANETs allows communication of moving vehicular nodes. Movement of nodes leads in changing network size and scenario. Whenever a new node joins the network, there is a threat of malicious node attack. So, we need an environment that is secure and trust worthy. Therefore a new cluster based secure technique is proposed where cluster head is responsible for providing communication between the vehicular nodes. Performance parameters used in this paper are message drop ratio, packet delay ratio and verification time.

Chaum's Visual Voting is a scheme in which a voter obtains a paper receipt from a voting machine. This receipt can be used to verify that his vote was counted in the final tally, but cannot be used for vote selling - i.e., the voter cannot prove that he voted for a certain party. The Chaum's system requires special purpose printers and application of ran- domized partial checking (RPC) method. RPC provides provable anonymity, but requires quite many tallying authorities. In this paper we propose a complete design of a voting system that preserves advantages of the Chaum's scheme, but eliminates the use of special printers and RPC. It seems that in our scheme it is easier to convince an average voter that a voting machine has prepared correctly his ballot and that his vote has been counted. We also show how to achieve scalability of the system.

We propose a version of ring signatures for which the set of potential signers may be reduced: the real signer can prove that he or she has created the signature, while every other member of the ring can prove not to be the signer. Possibility to run these protocols is triggered by publishing certain secret information. The proposed scheme is an intermediate solution between the classical ring and group signatures, and can be used for instance for e-auction schemes.

Vehicular Ad Hoc Networks (VANETs) are a particular subclass of mobile ad hoc networks that raise a number of security challenges, notably from the way users authenticate the network. Authentication technologies based on existing security policies and access control rules in such networks assume full trust on Roadside Unit (RSU) and authentication servers. The disclosure of authentication parameters enables user's traceability over the network. VANETs' trusted entities (e.g. RSU) can utilize such information to track a user traveling behavior, violating user privacy and anonymity. In this paper, we proposed a novel, lightweight, Adaptive Group-based Zero Knowledge Proof-Authentication Protocol (AGZKP-AP) for VANETs. The proposed authentication protocol is capable of offering various levels of users' privacy settings based on the type of services available on such networks. Our scheme is based on the Zero-Knowledge-Proof (ZKP) crypto approach with the support of trade-off options. Users have the option to make critical decisions on the level of privacy and the amount of resources usage they prefer such as short system response time versus the number of private information disclosures. Furthermore, AGZKP-AP is incorporated with a distributed privilege control and revoking mechanism that render user's private information to law enforcement in case of a traffic violation.

Vocal learning is well known among passerine and psittacine birds, but most data on mammals are equivocal. Speci¢c bene¢ts of vocal learning are poorly understood for most species. One case where vocal learning should be favoured by selection is where calls indicate group membership and group mates are unrelated. Female greater spear-nosed bats, Phyllostomus hastatus, live in stable groups of unrelated bats and use loud, broadband calls to coordinate foraging movements of social group mates. Bats bene¢t from group foraging. Calls di¡er between female social groups and cave colonies, and playback experiments demonstrate that bats perceive these acoustic di¡erences. Here I show that the group distinctive structure of calls arises through vocal learning. Females change call structure when group composition changes, resulting in increased similarity among new social group mates. Comparisons of transfers with agematched half-sibs indicate that call changes are not simply due to maturation, the physical environment or heredity. These results suggest that studies testing vocal learning in mammals could pro¢t by focusing on vocalizations that signify group membership.

In the cloud computing, security is one of the biggest obstacles that hamper the widespread adoption of cloud. Several business and research organization are reluctant in completely trusting the cloud computing to shift digital assets to the third-party service providers. Hence, the objective of this is to present the security issues related to data privacy and integrity in cloud computing. 20 selected papers have been reviewed to be analysing the technique used in providing data privacy and integrity. The issues or problems related to the technique are presented.

In the cloud computing, security is one of the biggest obstacles that hamper the widespread adoption of cloud. Several business and research organization are reluctant in completely trusting the cloud computing to shift digital assets to the third-party service providers. Hence, the objective of this is to present the security issues related to data privacy and integrity in cloud computing. 20 selected papers have been reviewed to be analysing the technique used in providing data privacy and integrity. The issues or problems related to the technique are presented. 

The advent of the cloud computing makes storage outsourcing becomes a rising trend, which promotes the secure remote data auditing a hot topic that appeared in the research literature. Recently some researches consider the problem of secure and efficient public data integrity auditing for shared dynamic data. In this paper, signifies that the collusion attack in the exiting scheme and provide an efficient public integrity auditing scheme with secure group user revocation based on vector commitment and verifier-local revocation group signature. Analysis shows a concrete scheme based on the scheme definition. The scheme supports the public checking and efficient user revocation and also some nice properties, such as confidently, efficiency, count ability and traceability of secure group user revocation.

Without trust, buyers may not join a coalition. Despite the tremendous need for trustworthy relationships in buyer coalitions, no current buyer coalition scheme explicitly tackles confidence issues with blockchain technology. This study proposes an algorithmic design, the blockchain-based trusty buyer coalition scheme, to satisfy the trust requirement among different actors while forming the coalition. All activities forming a coalition through a decentralized public ledger can be explicitly examined. Consequently, the proposed algorithm can ensure anonymity within a community, resulting in trusting relationships. Furthermore, the proposed algorithm can ensure correctness and accountability by recognizing misbehavior and enforcing alternative forms of punishment. Additionally, the discovered algorithm can be applied to mobile commerce applications.

In order to improve road traffic safety, reduce congestion, improving driving experience, intelligent transportation systems and vehicular networking concepts arises at the historic moment. In vehicle larger density scene, can't guarantee safe reliable and information transmission timely, sometimes can also cause problems such as the broadcast storm. Represented by LTE-A evolution of new generation of mobile communication network rapid development. It performance optimization in the system capacity, the peak rate, transmission delay and other key. In this paper, we proposed a privacypreserving and cross-domain group authentication scheme. It can effectively solve the security problems. Theoretical analysis and simulation results are shown that compared with other authentication protocol, our scheme has more security properties and better performance.

A Publicly Verifiable Secret Sharing (PVSS) scheme allows anyone to verify the validity of the shares computed and distributed by a dealer. The idea of PVSS was introduced by Stadler in [18] where he presented a PVSS scheme based on Discrete Logarithm. Later, several PVSS schemes were proposed. In [2], Behnad and Eghlidos present an interesting PVSS scheme with explicit membership and disputation processes. In this paper, we present a new PVSS having the advantage of being simpler while offering the same features. 1

Attribute-Based Encryption (ABE) is an advanced cryptographic technique that secures data by leveraging user attributes rather than conventional cryptographic keys. Expanding upon this, Multi-Authority Attribute-Based Encryption (MA-ABE) introduces multiple governing bodies, each managing distinct sets of attributes, to enhance flexibility and control in large-scale systems. The primary objective of this research is to address the challenges of privacy, anonymity, and access control in Identity and Access Management (IAM) through a novel MA-ABE framework. This study fills a critical gap in the current literature by providing a decentralized solution that effectively distributes authority and integrates advanced cryptographic techniques to safeguard sensitive data against unauthorized access and malicious attacks. The methodology employed integrates Elliptic Curve Cryptography (ECC) and the Elliptic Curve Diffie-Hellman (ECDH) key exchange for secure key generation and sharing. A novel approach for signing data with temporal context is introduced, utilizing Digital Signature Standard (DSS) with timestamping to enhance data integrity and authentication. The proposed model also incorporates Advanced Encryption Standard (AES) in EAX mode to ensure data confidentiality and integrity during encryption and decryption processes. The integration of these algorithms within a decentralized MA-ABE framework represents a significant advancement in the field of cryptographic systems for IAM. The findings demonstrate that the proposed MA-ABE system effectively maintains data security, user privacy, and anonymity. The experimental results show robust performance in handling dynamic access scenarios, enforcing strict access control, and preserving user anonymity without compromising system efficiency.

Public Key Infrastructure (PKI) schemes were first proposed in 1978 and standardized in 1988, yet, unlike most cryptographic schemes, PKI schemes were never rigorously defined. Achieving provable security for PKI is necessary and long overdue, as PKI provides the foundation for important applications of public key cryptography, such as TLS/SSL. In response, we present the first precise specifications of a secure PKI scheme, suitable for a variety of PKI designs. PKI schemes have significantly evolved since X.509, with more complex goals, e.g., transparency, to ensure security against corrupt issuers. In addition to the basic PKI properties, our definitions encompass these more recent and advanced aspects. Our results have important implications. First, our specifications allow a better scrutiny and comparison of the multitude of new PKI designs recently proposed, such as Google's Certificate Transparency (CT) and related PKIs, as well as future designs. Second, the specifications facilitate proper analysis of protocols and systems that use PKI, such as TLS/SSL, code signing, IPsec, DNSSEC, RPKI, BGPsec, permissioned blockchains, voting, recommendations, which is of critical importance as most real-world security schemes inherently rely on PKI. Finally, we use our specifications to formalize and prove X.509 version 2 PKI, showing that provable security is achievable for 'real' PKI designs. Index Terms-I. INTRODUCTION Public Key Infrastructure (PKI) provides an essential foundation for applications which rely on public key cryptography, and, specifically, it is crucial to ensure security in open networks and systems. Since the early PKI ideas were proposed in 1978 [1], the deployment of PKI has been dominated by the X.509 standard [2], whose first version was published in 1988. The practical importance of PKI grew after its adoption by Internet standards, most notably, the TLS/SSL protocol [3], which is the most widespread protocol used to secure connections between servers and clients, most commonly web browsers. The resulting 'web-PKI' is necessary to provide confidentiality, integrity and authenticity of web services, and as such, is critical for the secure use of the web. Unfortunately, the web-PKI deployment has inherent weaknesses. In particular, any certificate authority (CA) is trusted to issue certificates for any domain [4], resulting in the weakestlink security model and making individual CAs prime targets ** The work was partially completed during a visiting position at the Dept.

Abstract: Proxy signature schemes allow delegation of signing rights. The paper proposes the notion of Identity Based Strong Bi-Designated Verifier Proxy Signature (IDSBDVPS) schemes. In such schemes, only the two designated verifiers can verify that the proxy ...

It is considered a group signature scheme in frame of which different sets of signers sign electronic documents with hidden signatures and the head of the signing group generates a group signature of fixed size. A new mechanism for imbedding the information about signers into a group signature is proposed. The method provides possibilities for reducing the signature size and to construct collective signature protocols for signing groups. New group signature and collective signature protocols based on the computational difficulty of discrete logarithm are proposed.

Anonymity is an important feature in many twoparty communication systems. Its main meaning is that either the message sender or the receiver (or both) is unidentifiable to other users, even between themselves. Many mechanisms have been proposed to hide the identity of the sender, receiver, or both. Similarly, anonymity is an important feature in multiparty computing environments, but, little research has been conducted on this topic even though many secure group communication schemes have been proposed. In this paper, we highlight the concepts of anonymity for secure group communication and propose to extend a recently invented innovative group key management mechanism, Access Control Polynomial [54], to multi-party group communication. This newly extended scheme can not only enforce anonymous group membership and group size but also implement secure and anonymous group communication. The experimental results and comparison with existing schemes show that the new scheme is elegant, flexible, efficient and practical. The paper also summarizes and classifies typical existing anonymous group communication schemes.

In this research manuscript, a new protocol is proposed for predicting the available space in the cloud and verifying the security of stored data. The protocol is utilized for learning the available data, and based on this learning, the available storage space is identified, after which the cloud service providers allow for data storage. The Integrity verification separates the private and the public data, which avoids privacy issues. The integration of the private data is done with the help of cloud service providers with respect to the third-party auditing (TPA). Earlier, public key cryptography and bilinear map technologies have been combined by the researchers, but the computation time and costs were high. To secure the integrity of the data storage, the client should execute several computations. Therefore, this research suggests a reliable and effective method called position-aware Merkle tree (PMT), which is implemented for ensuring data integrity. The proposed system uses a PMT that enables the TPA to perform multiple auditing tasks with high efficiency, less computational cost and computation time. Simulation results clearly shows that the developed PMT method consumed 0.00459 milliseconds of computation time, which is limited when compared to the existing models.

This thesis studies a particular functionality for privacy-preserving systems, that allows a user to demonstrate a proof showing that the user has been approved by a number of authorities, without revealing their identities. We first consider this functionality for two fundamental cryptosystems: digital signature schemes, and public key encryption schemes, and introduce a new notion “grade” for these systems. Within this scope, we formalize two new primitives, graded signatures and graded encryption. Graded signature schemes enable a user to consolidate a set of signatures on a message m originating from l different signers. The resulting consolidated signature object on m reveals nothing more than the grade of the signature and the validity of the original signatures without leaking the identity of the signers. On the other hand, graded encryption schemes allow a sender to specify a numerical grade i for the ciphertext during the encryption depending on the importance of the messag...

Linkable ring signatures is a useful cryptographic tool for constructing applications such as ones relative to electronic voting (e-voting), digital cashes (e-cashes) as well as cloud computing. Equipped with linkable ring signatures, e-voting, e-cash systems can simultaneously enjoy the privacy and the unreusability properties thanks to the anonymity and the linkability of linkable ring signatures. Likewise, cloud servers can enjoy a privacy-preserving ability, a flexible access control and an efficient security management with linkable ring signatures. Moreover, linkable ring signatures built in the identity-based setting would help to remove the expense of using the conventional public key infrastructure and also could be applied to the user management. This primitive hence would be suitable for huge-scale applications. In this paper, we present the first identity-based linkable ring signatures (IdLRS) in both integer lattice and ideal lattice setting. The proposed IdLRS is proved secure in the random oracle model and based on the hardness of the short integer solution and ring short integer solution assumption. We also implement the proposed idLRS as a proof of concept and then do some experiments to evaluate the running times and the sizes. INDEX TERMS Identity-based linkable ring signatures, e-voting, e-cash, cloud computing, lattices.

Linkable ring signatures is a useful cryptographic tool for constructing applications such as ones relative to electronic voting (e-voting), digital cashes (e-cashes) as well as cloud computing. Equipped with linkable ring signatures, e-voting, e-cash systems can simultaneously enjoy the privacy and the unreusability properties thanks to the anonymity and the linkability of linkable ring signatures. Likewise, cloud servers can enjoy a privacy-preserving ability, a flexible access control and an efficient security management with linkable ring signatures. Moreover, linkable ring signatures built in the identity-based setting would help to remove the expense of using the conventional public key infrastructure and also could be applied to the user management. This primitive hence would be suitable for huge-scale applications. In this paper, we present the first identity-based linkable ring signatures (IdLRS) in both integer lattice and ideal lattice setting. The proposed IdLRS is proved secure in the random oracle model and based on the hardness of the short integer solution and ring short integer solution assumption. We also implement the proposed idLRS as a proof of concept and then do some experiments to evaluate the running times and the sizes. INDEX TERMS Identity-based linkable ring signatures, e-voting, e-cash, cloud computing, lattices.

For increasing safety of driving, intelligent vehicles in vehicular ad hoc networks (VANETs) communicate with each other by sending announcements. The existence of a system that guarantees the trustworthiness of these announcements seems necessary. The proposed approach generating announcements should be preserved from internal and external attackers that attempt to send fake messages. In this paper, we use a group-based endorsement mechanism based on threshold signatures against internal attackers. We choose NTRUSign as a public key cryptosystem for decreasing signature generation and verification times. This approach optimizes the network overhead and consequently its performance. In this scheme, also the privacy of signers and endorsers that generate or endorse trustworthy announcements is preserved.