Improvement of Identity-Based Threshold Proxy Signature Scheme with Known Signers

In 2006, Bao et al proposed an identlty-based threshold proxy signature scheme with known signers. In this paper, we show that Bao et al＇s scheme is vulnerable to the forgery attack. An adversary can forge a valid threshold proxy signature for any message with knowing a previously valid threshold proxy signature. In addition, their scheme also suffers from the weakness that the proxy signers might change the threshold value. That is, the proxy signers can arbitrarily modify the threshold strategy without being detected by the original signer or verifiers, which might violate the original signer＇s intent. Furthermore, we propose an improved scheme that remedies the weaknesses of Bao et al＇s scheme. The improved scheme satisfies all secure requirements for threshold proxy signature.

Secure Chained Threshold Proxy Signature without and with Supervision

Threshold Proxy Signature (TPS) scheme facilitates a manager to delegate his signing capability to a group of n2 sub-ordinates without revealing his own private key, such that a subgroup of at least t2 ≤ n2 subordinates is required to generate a proxy signature. In reality, the situation can be more complicated. First of all, the subgroup may further delegate their proxy signing capabilities to another group of n3 subordinates such that at least another subgroup of at least t3 ≤ n3 subordinates are of the proxy signing capabilities (in the form of a chain). t2 can be unequal to t3 depending on the concrete requirement. This is a group-to-group delegation problem. In addition, a supervising agent (SA) may be introduced in the above chain to supervise the subordinates, such that proxy signing can only be successfully executed with SA’s agreement. This is a delegation with supervision problem in the threshold delegation chain described above. These two extensions of delegation problems are not solved yet. This paper designs two provably secure cryptographic schemes Chained Threshold Proxy Signature (CTPS) scheme and Chained Threshold Proxy Signature with Supervision (CTPSwS) scheme to solve these two delegation problems.

IMPROVEMENT OF NONREPUDIABLE THRESHOLD MULTI-PROXY THRESHOLD MULTI-SIGNATURE SCHEME WITH SHARED VERIFICATION

In 2005, Bao, et al. [Appl. Math. and Comput., vol.169, No.2, 2005] showed that Tzeng, et al.’s nonrepudiable threshold multi-proxy multi-signature scheme with shared verification was insecure, and proposed an improved scheme with no Share Distribution Center (SDC). This paper shows that Bao, et al.’s scheme suffers from the proxy relationship inversion attack and forgery attack, and pro- poses an improvement of Bao, et al.’s scheme.

SECURITY ANALYSIS AND IMPROVEMENT OF A NEW THRESHOLD MULTI-PROXY MULTI-SIGNATURE SCHEME

Kang, et al. [Journal of Electronics(China), 23(2006)4] proposed a threshold multi-proxy multi-signature scheme, and claimed the scheme satisfies the security requirements of threshold multi-proxy multi-signature. However, in this paper, two forgery attacks are proposed to show that their schemes have serious security flaws. To overcome theses flaws, an improvement on Kang, et al.’s scheme is proposed.

Multi-proxy quantum group signature scheme with threshold shared verification

A multi-proxy quantum group signature scheme with threshold shared verification is proposed. An original signer may authorize a proxy group as his proxy agent. Then only the cooperation of all the signers in the proxy group can generate the proxy signature on behalf of the original signer. In the scheme, any t or more of n receivers can verify the message and any t - 1 or fewer receivers cannot verify the validity of the proxy signature.

A new threshold proxy signature scheme from bilinear pairings

Based on the GDH signature (short signature scheme) a probabilistic signature scheme is proposed in this paper with security proof.Then a new threshold proxy signature from bilinear pairings is proposed as well by us ing the new probabilistic signature scheme and the properties of the Gap Diffie-Hellman (GDH)group (where the Computational Diffie-Hellman problem is hard but the Decisional Diffie-Hellman problem is easy to solve).Our constructions are based on the recently proposed GDH signature scheme of Bonel et al.s article.Bilinear pairings could be built from Weil pairing or Tate pairing.So most our constructions would be simpler,but still with high security.The proposed threshold proxy signature is the first one which is built from bilinear pairings.At the end of this paper security and performance of the threshold proxy signature scheme is also analyzed.

Identity-based threshold signature and mediated proxy signature schemes

Proxy signature schemes allow an original signer to delegate his signing rights to a proxy signer. However, many proxy signature schemes have the defect which is the inability to solve the proxy revocation problem. In this article, we firstly propose an identity-based threshold signature scheme and show that it has the properties of unforgeability and robustness. In our threshold signature scheme, we adopt such a method that the private key associated with an identity rather than the master key is shared. Then, based on the threshold signature scheme, an identity-based mediated proxy signature scheme is proposed where a security mediator （SEM） is introduced to help a proxy signer to generate valid proxy signatures, examine whether a proxy signer signs according to the warrant, and check the revocation of a proxy signer. It is shown that the proposed scheme satisfies all the security requirements of a secure proxy signature. Moreover, a proxy signer must cooperate with the SEM to generate a valid proxy signature, which makes the new scheme have an effective and fast proxy revocation.

A secure threshold Paillier proxy signature scheme

As e-commerce applications and the underlying public key infrastructure have become more popular over time,many digital mechanisms emulating traditional business activities have been developed and deployed. To build a full-fledgedsecure digital world,secure implementations of more commercial activity primitives are required. In this paper,we present asecure proxy signature scheme and its threshold version based on the homomorphic Paillier cryptosystem,which can be used inmany e-commerce applications such as e-voting,e-bidding/auction,and privacy-preserving data mining. These two schemes areexistentially unforgeable against chosen-message attacks and chosen-warrant attacks in the random oracle model. Although it isbased on factoring,the threshold Paillier proxy scheme operates without requiring any trusted dealer or combiner. Thus,these twoschemes are practical for integration in modularized secure multi-party protocols.

The security analysis of a threshold proxy quantum signature scheme

In the YW threshold proxy quantum signature scheme proposed by Yang and Wen,it is found that the basic signature key is the same as the basic verification key,which means that the bitwise exclusive OR(XOR) of the t proxy signature keys is exactly the XOR of the t proxy verification keys.Therefore,the proxy signers can deny their signature and the specific verifiers can forge a legal signature.Furthermore,an attacker can obtain a legal threshold proxy signature for an arbitrary new message.These findings show that there are hidden security loopholes that should be carefully constructed in designing more efficent YW-scheme.

A Universal Composability Framework for Analysis of Proxy Threshold Signature

The universal composability framework is a new approach for designing and analyzing the security of cryptographic protocols.In this framework,the security of protocols is maintained under a general protocol composition operation.In the paper,we propose the universal composability framework for the analysis of proxy threshold signature and present a universally composable secure proxy threshold signature scheme which is the first one in this area.The proposed scheme is suitable for the mobile agents,which should migrate across different environment through network.Furthermore,we give the concrete analysis of the reduction to prove the security of the proposed scheme.

Threshold proxy quantum signature scheme with threshold shared verification

A threshold proxy quantum signature scheme with threshold shared verification is proposed. An original signer could authorize a group as its proxy signers. Then only t or more of n persons in the proxy group can generate the proxy signature on behalf of the original signer and any t-1 or fewer ones cannot do that. When the proxy signature needs to be verified,any t or more of n persons belonging to the verification group can verify the message and any t-1 or fewer ones cannot verify the validity of the proxy signature.

代理签名的现状与进展

首先描述了代理签名产生的背景、现状与进展。然后,介绍了代理签名的概念、要求、分类与述评,给出了几种典型的代理签名方案,并进行相应的分析与述评。最后,指出了目前代理签名方案存在的问题, 并且对未来的研究方向进行了展望。

基于RSA密码体制的门限代理签名

在一个(t,n)门限代理签名体制中,原始签名者可以将他的签名权利以门限的方式委托给n个代理签名者,至少t个代理签名者合作,可以产生相应的代理签名,而任何少于t个代理签名者则不能.目前已经有很多基于离散对数问题的门限代理签名方案,但是并没有出现一个真正意义上的基于RSA密码体制的门限代理签名方案.鉴于RSA在理论及应用中的重要性,基于RSA构造门限代理签名体制是必要的.文中借助于RSA秘密共享的思想,构造了一个安全、有效的RSA门限代理签名方案.在文中的方案中,没有使用可信权威,所有的秘密参数都是由参与者分布式产生的.

具有已知代理人的不可否认门限代理签密方案(英文)

1996年,Mambo等人提出了代理签名概念.但是,代理签名仅能提供授权的认证而不能提供保密性.Chan和Wei提出一个门限代理签密方案(记为Chan-Wei方案),扩展了代理签名的概念.指出他们的方案不满足强不可伪造性、强不可否认性和强识别性.基于Chan-Wei方案,提出一个能够克服Chan-Wei方案缺点的不可否认门限代理签密方案.给出方案的完备性证明和安全性分析.此外,与Chan-Wei方案相比,所提出的方案能够确切地发现哪些代理人提供假子密钥或篡改子密钥.

一个门限代理签名方案的改进

1996年 Mambo,Usuda和 Okamoto提出了代理签名的概念 ,即在一个代理签名方案中 ,一个被指定的代理签名人可以代表原始签名人生成有效的代理签名 .Mambo,U suda和 Okam oto指出代理签名方案应满足不可否认性、可验证性、不可伪造性、可区分性等性质并给出 3种类型的代理签名 :完全代理签名 ,部分代理签名和带有授权证书的代理签名 .Sun,L ee和 Hwang提出了一个门限代理签名方案 (记为 S- L- H方案 ) ,分别克服了由Zhang和 Kim等提出的门限代理签名方案的缺点并给出了一个改进方案 .这里指出 S- L- H方案不能抵抗公钥替换攻击 ,并给出了一个改进的门限代理签名方案 .进一步利用零知识的思想给出了抵抗公钥替换攻击的一般方法 .改进后的方案除具有 S- L- H方案的安全性外 ,还具有不可否认性、不使用安全信道、能抵抗公钥替换攻击和合谋攻击等特点 .

基于RSA的门限多重代理多重签名方案

利用陈克菲提出的基于仿射空间的门限RSA密码体制,设计了一个新的多重代理、多重签名方案。该方案中有一个原始签名组G_o={O_1,O_2,…,O_(N1)}和一个代理签名组G_P={P_1,P_2,…,P_(N2))。原始签名组中任何T_1(T_1≤N_1)个成员都可代表原始签名组将签名权委托给代理签名组,而原始签名组中任何少于T_1个成员都不可能进行有效的授权;代理签名组中任何T_2(T_2≤N_2)个成员都可代表代理签名组依据授权进行代理签名,而代理签名组中任何少于T_2个成员都不可能进行有效签名。该方案签名方案能够满足不可否认性、不可伪造性和可识别性的要求。

对一种基于身份的已知签名人的门限代理签名方案的分析

在TAMC’06上,Bao等人以双线性对为工具,首次提出了一种基于身份的已知签名人的门限代理签名方案(以下标记为BCW方案),并得出了满足强不可伪造性以及原始签名人发送签名了的授权证书时并不需要安全信道等安全性结论。本文对BCW方案进行了安全性分析,成功地给出了一种攻击,攻击者通过公开渠道获得一个合法的原始签名人发送给代理签名人的签名了的授权证书以及代理签名人已经生成的一个有效的代理签名后,能够伪造出一个新的对相同消息的代理签名,而原始签名人变为攻击者自己。由于验证者并不能验证代理签名人到底是代表谁生成了代理签名,这样,攻击者就获得了与合法原始签名人相同的权益。为了避免这种攻击,本文提出了改进的措施,分析表明,改进措施能有效地弥补了该方案的安全缺陷。