Group-oriented (t, n) threshold digital signature scheme and digital multisignature

A new group signature with one time secret key is proposed. The main merits are that it only needs the trusted center issuing the partial secret key one time for each group member; and that the group member can generate his different secret key each time when he wants to sign a message. The group public key is constant and the size of the signature is independent of the number of group members. The total computation cost of signature and verification requires only 8 modular exponentiations.

A group signature scheme allows a group member to sign a message anonymously on behalf of the group. In case of a dispute, the group manager can reveal the actual identity of signer. In this paper, we propose an efficient group signature scheme, which divide the document M into m blocks and add some redundant bits to each message block, to avoid the conspiracy attack. The security of the proposed scheme is based on the difficulty of computing the discrete logarithm modulo for a composite number. The size of the group signature and the verification time of the group signature are equivalent to that of an individual signature.

Group signatures are generalised credential/member authentication schemes with wide applications. Membership revocation problem is a major issue of group signatures, and is often resolved through an additional protocol which would encumber the whole group signature both in computation and storage, as Camenisch et al. did to ACJT's group signature scheme (the first ever practical group signature based on RSA problem put forward by Ateniese et al. at Crypto'00) by dynamic accumulator. Boneh et al. applied Camenisch et al.'s dynamic accumulator based revocation reversely, resulted in short group signature. We formally define the method used by Boneh et al., named reversed dynamic accumulator in this paper, and apply it on some previous group signatures to obtain improved ones with revocation capability, reduced bandwidth (signature size) and less signature generation computations. We also address the problems unsolved in Boneh et al.'s work, e.g. how to open a group signature since the current certificate may no longer be the one stored when it is firstly generated.

A lattice-based group signature scheme (LGSS) is an active cryptographic primitive, where each group member can sign messages anonymously in the name of the entire group and each valid signature should be traced to some group member on the lattice. In each LGSS, the size of the group signature usually depends on the number of group members and the security parameter. Thus, designing a constant-size LGSS is an interesting problem. At PKC 2018, Ling, Nguyen, Wang and Xu presented the first constant-size group signature scheme under lattice assumptions. Its design is based on a zero-knowledge argument of the knowledge of a valid message-signature pair for the Ducas-Micciancio signature scheme, which follows the sign-then-encrypt-then-prove protocol. In contrast to this work, we construct a new constant-size LGSS. The scheme adopts the sign-hybrid-encrypt approach and makes use of the Lyubashevsky signature scheme. Our work is efficient in the signing algorithm, more precise on the open algorithm and shorter in public key, secret key and signature size than previous studies. Furthermore, we prove that the scheme has full anonymity and full traceability under the Ring Learning With Errors and Ring Short Integer Solution assumptions in the random oracle model.

A group signature scheme allows a group member to sign a message anonymously on behalf of the group. In case of a dispute, the group manager can reveal the actual identity of signer. To enhance the efficiency of group signature schemes, in this paper, we propose an efficient group signature scheme which adds some redundant bits to each divided message block, to avoid the conspiracy attack. In our scheme, the size of a signature is the same as that of an individual signature and the signature verification process is simplified by a group public key. The security of the proposed scheme is based on the difficulty of computing the discrete logarithm modulo for a composite number.

An identity-based dynamic group signature scheme for reputation evaluation systems

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 non-interactive 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.

Ring Confidential Transaction (RingCT) protocols are widely used in cryptocurrencies to protect user privacy. Consequently, a corresponding digital signature scheme, such as a ring signature scheme that hides the signers’ identities, is required. Accordingly, the security of a RingCT protocol depends on the confidentiality of the secret signing keys of the underlying ring signature scheme. However, existing solutions like hardware wallets, Trusted Execution Environments (TEEs), and threshold signature schemes have limitations such as specified expensive hardware, targeting attacks at CPUs on insufficiently secure hardware, and overheads caused by multiple parties. On the contrary, program obfuscation for signature schemes offers advantages over these existing approaches. Concretely, we propose a novel obfuscator that secures the secret keys of the concise linkable spontaneous anonymous group (CLSAG) signature scheme, which is the latest ring signature scheme used in Monero’s RingCT protocol. To achieve enhanced security, the proposed obfuscator leverages Paillier homomorphic encryption to transform secret keys into an obfuscated form resistant to attacks. The security of the proposed obfuscator has been formally proved. Computational efficiency has been both theoretically analyzed and experimentally evaluated with positive results on various testing platforms.

This paper presents a strong designated verifier group signature scheme, in which signature is generated by any member of the group and it is verified by only a specific receiver, called a designated verifier using the public parameters of the group and his own secret key. The verifier assumes that the signature indeed is from the group itself, not from any individual group member. In this scheme, anonymity of the signer is completely preserved. The verifier cannot link a signature to the signer. The scheme is secure as an adversary cannot verify the signature even if the secret key of the signer is compromised or leaked. Also, neither the group manager nor any member of the group can produce a valid signature on behalf of another member. Only in case of legal disputes, the group manager can disclose the identity of a group member who has signed a document. The major benefit of this scheme is that the length of the group signature is independent of number of group members and it remains unaffected if some members left the group or new members join the group. Security of the proposed scheme lies in the complexity of solving three computationally hard problems, namely, Computational Diffiee-Helmann (CDH) problem, Discrete Logarithm Problem (DLP) and Integer Factorization Problem (IFP). This scheme can be useful in organizations where there is a need to send confidential documents to a specific recipient. This scheme can also be applicable to real life scenarios, such as, e-commerce applications, e-banking and e-voting.

Ring signatures and group signatures are prominent cryptographic primitives offering a combination of privacy and authentication. They enable individual users to anonymously sign messages on behalf of a group of users. In ring signatures, the group, i.e. the ring, is chosen in an ad hoc manner by the signer. In group signatures, group membership is controlled by a group manager. Group signatures additionally enforce accountability by providing the group manager with a secret tracing key that can be used to identify the otherwise anonymous signer when needed. Accountable ring signatures, introduced by Xu and Yung (CARDIS 2004), bridge the gap between the two notions. They provide maximal flexibility in choosing the ring, and at the same time maintain accountability by supporting a designated opener that can identify signers when needed. We revisit accountable ring signatures and offer a formal security model for the primitive. Our model offers strong security definitions incorporating protection against maliciously chosen keys and at the same time flexibility both in the choice of the ring and the opener. We give a generic construction using standard tools. We give a highly efficient instantiation of our generic construction in the random oracle model by meticulously combining Camenisch’s group signature scheme (CRYPTO 1997) with a generalization of the one-out-of-many proofs of knowledge by Groth and Kohlweiss (EUROCRYPT 2015). Our instantiation yields signatures of logarithmic size (in the size of the ring) while relying solely on the well-studied decisional Diffie-Hellman assumption. In the process, we offer a number of optimizations for the recent Groth and Kohlweiss one-out-of-many proofs, which may be useful for other applications. Accountable ring signatures imply traditional ring and group signatures. We therefore also obtain highly efficient instantiations of those primitives with signatures shorter than all existing ring signatures as well as existing group signatures relying on standard assumptions.

The work presents an efficient identification threshold signature scheme based on the elliptic curve cryptosystem, with a view to optimizing these techniques for implementation within a network. (Any t out of n users in a group can represent this group to sign the group signature) as compared with the existing threshold signature scheme based on the public key system of RSA and ELGmal, our scheme need less parameters but can provide more efficient and super security. Moreover it is constructed on the two base points but other threshold signature scheme constructed on the only one point. The distinguishing feature of the proposed scheme is that the threshold value denotes the minimum number of members required to produce a valid group signature. All message recipients then can verify the signature.

ABSTRACTIndividual recognition mechanisms have played a key role in odontocete ecology, maintaining social cohesion and therefore ensuring the maintenance of long‐term social ties. The current study was the first to identify and describe stereotyped whistle contour types by both a visual similarity value judgment task and acoustic and temporal parameters in free‐ranging Risso's dolphins (Grampus griseus) in Mexican Pacific waters of the Gulf of the California. In total, 64.1% (118) of all analyzed whistles (184) were classified as stereotyped whistles (STW); 82.2% of them (97) met the SIGnature IDentification bout criteria and were, subsequently, ascribed into one of the five possible signature whistle (PSW) types. These signature call types accounted for 52.7% (97/184) of the acoustic repertoire. All PSW types were classified as sine (wavering sinusoidal whistles) and showed mean acoustic and temporal variable values similar to other studies of Risso's dolphins that did not differentiate signature whistles (SWs). External naive independent observers who lacked expertise in bioacoustics have confirmed the adopted classification created at high agreement level and near perfect match. Accordingly, the present study provided additional acoustic evidence of individually distinct vocalization in this species, reinforcing the need for further studies to help deepen and broaden the knowledge about the function, production and incidence of individual and “group signatures” and cognitive and recognition processes in the herein investigated species, among others.

Group signatures are a central cryptographic primitive where users can anonymously and accountably sign messages in the name of a group they belong to. Several efficient constructions with security proofs in the standard model (i.e., without the random oracle idealization) appeared in the recent years. However, like standard PKIs, group signatures need an efficient revocation system to be practical. Despite years of research, membership revocation remains a non-trivial problem: many existing solutions do not scale well due to either high overhead or constraining operational requirements (like the need for all users to update their keys after each revocation). Only recently, Libert, Peters and Yung (Eurocrypt’12) suggested a new scalable revocation method, based on the Naor-Naor-Lotspiech (NNL) broadcast encryption framework, that interacts nicely with techniques for building group signatures in the standard model. While promising, their mechanism introduces important storage requirements at group members. Namely, membership certificates, which used to have constant size in existing standard model constructions, now have polylog size in the maximal cardinality of the group (NNL, after all, is a tree-based technique and such dependency is naturally expected). In this paper we show how to obtain private keys of constant size. To this end, we introduce a new technique to leverage the NNL subset cover framework in the context of group signatures but, perhaps surprisingly, without logarithmic relationship between the size of private keys and the group cardinality. Namely, we provide a way for users to efficiently prove their membership of one of the generic subsets in the NNL subset cover framework. This technique makes our revocable group signatures competitive with ordinary group signatures (i.e., without revocation) in the standard model. Moreover, unrevoked members (as in PKIs) still do not need to update their keys at each revocation.KeywordsGroup SignatureGroup ElementRandom OracleBroadcast EncryptionCryptology ePrint ArchiveThese keywords were added by machine and not by the authors. This process is experimental and the keywords may be updated as the learning algorithm improves.

Group signature is an important anonymous technique. Two primitive properties of group signature is anonymity and unforgeability. It allows a group member to sign messages anonymously on behalf of the group such that any one can verify the signature but no one (except group manager) can find out which group member produce it. However, group manager can reveal the identity of the originator of a signature in case of a dispute. Recently Elaalim et.al proposed a short ID-based group signature, and claimed that the scheme is secure against forgeability attack and linkability attack. Unfortunately, in the paper, we show that the scheme is insecure, it exists universal forgeability, namely, anyone can forge a group signature on arbitrary message; and the scheme is linkable, namely, given two different group signatures, anyone can distinguish whether they are produced by the signer. Finally, the corresponding attacks are mounted, and the reason to such attacks are analyzed.

Certificateless threshold signature scheme from bilinear maps