Nonrepudiable Threshold Proxy Signature Scheme Research Articles

Cryptanalysis and improvement of a threshold proxy signature scheme

A ( t, n) threshold proxy signature scheme allows any t or more proxy signers to cooperatively sign messages on behalf of an original signer, but t − 1 or fewer proxy signers cannot. In a recent work [C.H. Yang, S.F. Tzeng, M.S. Hwang, On the efficiency of nonrepudiable threshold proxy signature scheme with known signers, Systems and Software 73(3) (2004) 507–514], C.H. Yang, S.F. Tzeng and M.S. Hwang proposed a new threshold proxy signature scheme (called as YTH scheme), which is more efficient in algorithm and communication than Hsu et al.'s scheme proposed in 2001. However, YTH scheme still has some security weaknesses. In this paper, we show that YTH scheme cannot resist frame attack and public-key substitute attack. A new improvement with high safety and efficiency is proposed. The new scheme remedies the weaknesses of YTH scheme, especially, it can resist public-key substitute attack successfully by Zero-Knowledge Proof. Furthermore, the system doesn't need a security channel and computational complexity can be lowered.

Cryptanalysis of Two Nonrepudiable Threshold Proxy Signature Schemes

This paper will show that Hsu and Wu’s efficient nonrepudiable threshold proxy signature scheme with known signers and Yang, Tzeng and Hwang’s efficient nonrepudiable threshold proxy signature scheme with known signers are insecure. The malicious original signer can forge a valid threshold proxy signature for any message and any warrant after getting a valid proxy signature. In addition, since Yang et al.’s scheme is more efficient than Hsu and Wu’s scheme in terms of computational complexities and communication costs, this paper only presents a simple countermeasure to improve Yang et al.’s scheme.

Improvement of Yang et al.’s threshold proxy signature scheme

Since the first ( t, n) threshold proxy signature scheme was proposed, the threshold proxy signature has enjoyed a considerable amount of interest from the cryptographic research community. In 2001, Hsu et al. proposed a non-repudiable threshold proxy signature scheme with known signer, but the efficiency is rather low and a system authority (SA) is also required in this scheme. Recently, to overcome these shortcomings, Yang et al. proposed an improvement of Hsu et al.’s scheme that is very efficient and without employing a SA. However, in this paper, we shows that Yang et al.’s scheme is not secure against the warrant attack. That is, the adversary can replace the warrant of the proxy signature. To resist this attack, based on Yang et al.’s scheme, we propose a new and more efficient scheme without a secure channel.

Improvement of Tzeng et al.’s nonrepudiable threshold proxy signature scheme with known signers

In 2000, Hwang et al. proposed a nonrepudiable threshold proxy signature scheme with known signers. However, Tzeng Hwang, Yang [An improvement of nonrepudiable threshold proxy signature scheme with known signers, Comput. Security 23 (2004) 174–178] showed that Hwang et al.’s scheme was vulnerable to the forgery attack, and a new secure threshold proxy signature scheme was proposed to remedy the weakness of their scheme. Unfortunately, we will show that Tzeng et al.’s scheme is also vulnerable to the forgery attack, the malicious original signer can forge a valid threshold proxy signature for any message with knowing a previously valid threshold proxy signature. Furthermore, we improve the security of the threshold proxy signature scheme that remedies the weakness of Tzeng et al.’s scheme.

Efficient nonrepudiable threshold proxy signature scheme with known signers against the collusion attack

In 1999, Sun proposed a nonrepudiable (t,n) threshold proxy signature scheme with known signers. Latter, Hwang et al. pointed out Sun’s scheme is vulnerable to the so-called collusion attack that (n−1) malicious proxy signers in the proxy group could conspire to impersonate the remainder one. Hwang et al. further proposed an improvement to withstand such an attack. In this paper, however, we will show that Hwang et al.’s improvement is still vulnerable to their proposed collusion attack and unable to achieve the nonrepudiation requirement as they claimed. Finally, we proposed a new efficient nonrepudiable threshold proxy signature scheme not only to eliminate the security leaks but also to be more efficient than Hwang et al.’s scheme in terms of computational complexities and communication costs.

An improvement of nonrepudiable threshold proxy signature scheme with known signers

In a ( t, n) threshold proxy signature scheme, which is a variant of the proxy signature scheme, the proxy signature key is shared among a group of n proxy signers delegated by the original signer. Any t or more proxy signers can cooperatively sign messages on behalf of the original signer. In 2000, Hwang et al. (Int J Inf 11 (2000) 1) proposed a secure nonrepudiable threshold proxy signature scheme with known signers. In this paper, we point out a cryptanalysis of their scheme. Furthermore, we improve the security of the threshold proxy signature scheme which remedies the weakness of Hwang et al.'s scheme.

On the efficiency of nonrepudiable threshold proxy signature scheme with known signers

In the ( t, n) proxy signature scheme, the signature signed by the original signer can be signed by t or more proxy signers out of a proxy group of n proxy signers. Recently, Hsu et al. proposed a nonrepudiable threshold proxy signature scheme with known signers. In this article, we shall propose an improvement of Hsu et al.'s scheme that is more efficient in terms of computational complexity and communication cost.

New nonrepudiable threshold proxy signature scheme with known signers

Based on Kim et al.'s threshold proxy signature scheme, Sun proposed an nonrepudiable threshold proxy signature scheme with known signers. In Sun's scheme, actual proxy signers cannot deny the signatures they have signed. However, his scheme is vulnerable against the conspiracy attack. Any t malicious proxy signers can collusively derive the secret keys of other proxy signers and impersonate some other proxy signers to generate proxy signatures. In this paper, we proposed a new nonrepudiable threshold proxy signature scheme that overcomes the above weakness. Furthermore, the proposed scheme is more efficient than Sun's in terms of computational complexities and communication costs.

A SECURE NONREPUDIABLE THRESHOLD PROXY SIGNATURE SCHEME WITH KNOWN SIGNERS

In the (t;n) proxy signature scheme, the signature, originally signed by a signer, can be signed by t or more proxy signers out of a proxy group of n members. Recently, an efficient nonrepudiable threshold proxy signature scheme with known signers was proposed by H.-M. Sun. Sun's scheme has two advantages. One is nonrepudiation. The proxy group cannot deny that having signed the proxy signature. Any verifier can identify the proxy group as a real signer. The other is identifiable signers. The verifier is able to identify the actual signers in the proxy group. Also, the signers cannot deny that having generated the proxy signature. In this article, we present a cryptanalysis of the Sun's scheme. Further, we propose a secure, nonrepudiable and known signers threshold proxy signature scheme which remedies the weakness of the Sun's scheme.

An efficient nonrepudiable threshold proxy signature scheme with known signers

A ( t, n) threshold proxy signature scheme allows t or more proxy signers from a designated group of n proxy signers to sign messages on behalf of an original signer. A threshold proxy signature scheme with the nonrepudiation property is a scheme with the capability that any verifier can identify the proxy group which is responsible for a proxy signature, while the proxy group cannot deny. So far, there have been two threshold proxy signature schemes proposed. Of these, Kim’s scheme is nonrepudiable, but Zhang’s scheme is not. In these two schemes, the t proxy signers from the group who actually sign the message are unknown and unidentified. This is very inconvenient for auditing purposes. For the responsibility of the actual signers and the traceability of adversarial signers, it is sometimes necessary to identify who the actual signers are. In this article, we propose the nonrepudiable threshold proxy signature scheme with known signers which is a nonrepudiable threshold proxy signature scheme with the property that the actual signers from the proxy group are known and identified.