Disavowal Protocols Research Articles

A Novel Undeniable (t, n)-Threshold Signature with Cheater Identification

A digital signature is one of the most widely used cryptographic primitives in asymmetry cryptography. According to the security requirements in different symmetry or asymmetry network models, various digital signatures have been developed in the literature. To protect the right of the signer, Chaum and Antrepen first introduced the concept of an undeniable signature, where interactive protocols are needed for the verification process. Besides, a signer can, also, perform a disavowal protocol to prove that they did not sign the message. On the other hand, threshold cryptography is, usually, used to protect the system from a single point of failure. In a (t,n)-threshold signature scheme, as long as t people in the group of n people participate, the signature can be smoothly signed. By combining these two features, an undeniable threshold signature enjoys the advantages from both sides. After our survey, we found that the existing undeniable threshold signature schemes are either insecure or apply impractical assumptions. Thus, in this manuscript, we aim at designing a novel and provably secure undeniable threshold signature scheme. The proposed scheme is formally proven to be unforgeable and invisible. Besides, our scheme supports cheater identification, which allows one to find the cheater, when a signing protocol fails. Moreover, the proposed scheme can be performed without the help of trusted third parties or secure cryptographic modules, which would be more practical when our scheme is deployed in real-world applications.

Рандомизированный аналог неоспоримой подписи Чаума - ван-Антверпена

We suggest an elliptic curve modification of the undeniable signature introduced by D. Chaum and H. van-Antwerpen. The signature generation algorithm is supplemented with a preliminary stage of randomization. For signature verification and disavowal protocols, two options are offered. Theorems showing that these protocols meet their purpose have been proven. A method for converting an undeniable signature into a regular digital signature is described, illustrated by the Schnorr electronic signature scheme as an example.

An efficient certificateless undeniable signature scheme

Certificateless cryptography addresses the private key escrow problem in identity-based systems, while overcoming the costly issues in traditional public key cryptography. Undeniable signature schemes were proposed with the aim of limiting the public verifiability of ordinary digital signatures. The first certificateless undeniable signature scheme was put forth by Duan. The proposed scheme can be considered as the certificateless version of the identity-based undeniable signature scheme which was introduced by Libert and Quisquater. In this paper, we propose a new scheme which is much more efficient comparing to Duan's scheme. Our scheme requires only one pairing evaluation for signature generation and provides more efficient confirmation and disavowal protocols for both the signer and the verifier. We also prove the security of our scheme in the strong security model based on the intractability of some well-known pairing-based assumptions in the random oracle model.

Relation between Verifiable Random Functions and Convertible Undeniable Signatures, and New Constructions

Verifiable random functions (VRF) and selectively convertible undeniable signature (SCUS) schemes were proposed independently in the literature. In this paper, we observe that they are tightly related. This directly yields several deterministic SCUS schemes based on existing VRF constructions. In addition, we create a new probabilistic SCUS scheme, which is very compact. The confirmation and disavowal protocols of these SCUS are efficient, and can be run either sequentially, concurrently, or arbitrarily. These protocols are based on what we call zero-knowledge protocols for generalized DDH and non-DDH, which are of independent interest.

Adapting a Novel Dual Authentication Method based on Smart Cards

In this paper, adapting a novel dual authentication method based on smart cards in public networks is proposed. This method uses the ElGamal public key cryptosystem and extend Chaum–van Antwerpen’s scheme to authenticate a signature between the signer and verifier using a dual protocol with a smart card that has tamper-resistant features. We propose the method to change the verification and disavowal protocol in Chaum–van Antwerpen’s scheme to authenticate both the signer and verifier. With these modifications, attempts to reject or deny a valid signature between the signer and verifier can be prevented or detected with high efficiency

Non‐interactive deniable ring signature without random oracles

AbstractRing signature scheme protects the privacy while signer is signing. In the ring signature scheme, the signer can randomly choose verification keys of entities and generate a signature on behalf of these entities. The generated signature can be verified by anyone by inputting all these verification keys. Consequently, a ring signature convinces a verifier that one member from these entities produces this signature without revealing which one. This property is good for the signer as his identity is not leaked. However, the signer also can make use of this capacity to generate a malicious signature on behalf of a ring. Because of the unconditional anonymity of ring signature, this signer cannot be traced to be responsible for his malicious signing. Group signature can avoid this problem because the group manager in the group signature can trace the actual signer by using the trapdoor. However, the group is fixed from the beginning and it needs a complicated setup algorithm. Deniable ring signature was introduced by Komano et al., which allows to revoke the anonymity of actual signer without the manager's help if necessary. The actual signer can confirm his signing for anyone through the confirmation protocol. On the other hand, non‐signers in the ring can disavow this signing by the disavowal protocol. Therefore, the actual signer can be traced. However, Komano's scheme was proven in random oracles, and the traceability protocols (confirmation and disavowal protocols) are interactive. To improve Komano's construction, this work proposes a new efficient non‐interactive deniable ring signature scheme in the standard model. It is a kind of ring signature and therefore, it does not require a setup algorithm, and the ring in the scheme is flexible. Copyright © 2013 John Wiley & Sons, Ltd.

An efficient conditionally anonymous ring signature in the random oracle model

A conditionally anonymous ring signature is an exception since the anonymity is conditional. Specifically, it allows an entity to confirm/refute the signature that he generated before. A group signature also shares the same property since a group manager can revoke a signer’s anonymity using the trapdoor information. However, the special node (i.e., group manager) does not exist in the group in order to satisfy the ad hoc fashion. In this paper, we construct a new conditionally anonymous ring signature, in which the actual signer can be traced without the help of the group manager. The big advantage of the confirmation and disavowal protocols designed by us are non-interactive with constant costs while the known schemes suffer from the linear cost in terms of the ring size n or security parameter s.

The security of the FDH variant of Chaum's undeniable signature scheme

In this paper, a new kind of adversarial goal called forge-and-impersonate in undeniable signature schemes is introduced. Note that forgeability does not necessarily imply impersonation ability. The security of the full-domain hash (FDH) variant of Chaum's undeniable signature scheme is then classified according to three dimensions, the goal of adversaries, the attacks, and the zero-knowledge (ZK) level of confirmation and disavowal protocols. Each security is then related to some well-known computational problem. In particular, the security of the FDH variant of Chaum's scheme with noninteractive zero-knowledge (NIZK) protocol confirmation and disavowal protocols is proven to be equivalent to the computational Diffie-Hellman (CDH) problem, as opposed to the gap Diffie-Hellman (GDH) problem as claimed by Okamoto and Pointcheval.