Signing Capability Research Articles

Cryptananlysis of a Proxy Blind Signature Scheme Based on DLP

Proxy signature allows an original signer to delegate his/her signing capability to a proxy signer such that the proxy signer can sign messages on behalf of the original signer. Blind signature allows a user to have a given message signed by the signer without revealing any information about the message. By using Schnorr blind signature, Tan et al. recently proposed a digital proxy blind signature scheme. They claimed that it satisfies the security properties of both blind signatures and proxy signatures. However, it is not the fact. This paper shows that the proposed scheme is vulnerable to universal forgery as well as linkability attacks. It also explains why their proofs of the security are incorrect.

Proxy signature schemes with time limitation

In this paper, we propose a key-revolution concept for proxy signature schemes to obtain a property of time limitation on delegation duration of proxy signatures. Proxy signature scheme is a kind of signature schemes in which an original signer delegates its signing capability to a designated signer called a proxy signer. Then, the proxy signer creates a digital signature on behalf of the original signer. The problems of time limitation on delegation duration are essential for proxy signature schemes. We propose a proxy signature scheme with time limitation in which a proxy key is renewed in each period until the end of period. Then, the proxy key is revoked automatically.

Comments on "A practical (t, n) threshold proxy signature scheme based on the RSA cryptosystem"

In a (t, n) threshold proxy signature scheme, the original signer can delegate his/her signing capability to n proxy signers such that any t or more proxy signers can sign messages on behalf of the former, but t-1 or less of them cannot do the same thing. Such schemes have been suggested for use in a number of applications, particularly, in distributed computing where delegation of rights is quite common. Based on the RSA cryptosystem, [M. -S. Hwang et al. (2003) recently proposed an efficient (t, n) threshold proxy signature scheme. We identify several security weaknesses in their scheme and show that their scheme is insecure.

A nonrepudiable threshold multi-proxy multi-signature scheme with shared verification

In this paper, we shall propose a threshold multi-proxy multi-signature scheme with shared verification. In the scheme allows the group of original signers to delegate the signing capability to the designated group of proxy signers. Furthermore, a subset of verifiers in the designated verifier group can authenticate the proxy signature. A threshold multi-proxy multi-signature scheme with the nonrepudiation property is a scheme where the proxy group cannot deny signing for the message and the verifier group can identify the proxy group for a proxy signature.

The security of a strong proxy signature scheme with proxy signer privacy protection

In 1996, Mambo et al. first introduced the concept of a proxy signature scheme, and discussed the delegation of the signing capability to a proxy signer. In 2001, Lee et al. constructed a strong non-designated proxy signature scheme. In 2002, Shum and Wei presented an enhancement to the Lee et al.'s scheme to hide the identity of the proxy signer. No one can determine the identity of the proxy signer only from the proxy signature. Moreover, a trusted authority can reveal the proxy signer's identity if needed. However, this paper will show that the Shum–Wei scheme cannot keep the property of the strong unforgeability. That is, not only the proxy signer but also the original signer can generate valid proxy signatures.

A new proxy signature scheme with revocation

In current proxy signature schemes, an original signer delegates her/his signing capability to a proxy signer, and then the proxy signer can sign messages on behalf of the original signer. Although these schemes have succeeded in proxy delegations, they are in general defective in proxy revocations. In this paper, we propose a proxy signature scheme which allows the original signer to revoke delegations whenever necessary.

위임등록 프로토콜을 이용한 대리서명 기법

실생활에서 권한의 위임을 통한 대리 서명 기법들이 최근 많이 연구되고 있다. 대리서명은 원 서명자가 자신의 서명 권한을 대리 서명자에게 위임하여 대리 서명자가 원 서명자를 대신하여 서명을 생성하는 것을 의미하며 기본적으로 원 서명자가 위임 정보에 대한 서명을 생성하고 이를 대리 서명자에게 전달하여 대리 서명자가 위임키로서 사용하게 하는 방법을 통하여 이루어진다. 이러한 대리서명 기법을 사용하기 위해서는 몇 가지 보안 사항들이 요구된다. 본 논문에서는 기존의 보안 요구 사항들을 모두 만족하고 원 서명자와 대리 서명자가 기존의 인증서를 발급 받은 환경에서 원 서명자가 대리 서명자에 대한 위임정보를 검증자에게 등록하는 프로토콜을 제안한다. 제안하는 방법에서는 위임내용에 대해 원 서명자가 디지털 서명을 하고 검증자는 이에 해당하는 내용을 검증한 후 대리 서명자에 대한 권한, 기간, 제약사항을 설정한다 대리 서명자는 위임내용에 대한 고지를 받고 허가된 범위 내에서 대리 서명이 이루어지게 된다. 또한 기존의 대리 서명 기법들과의 비교 분석을 통하여 제안하는 위임 등록 프로토콜에 대한 효율성을 제시한다. Proxy signature schemes based on delegation of warrant are frequently studied in these days. Proxy signatures are signature schemes that an original signer delegates his signing capability to a proxy signer, and the proxy signer creates a signature on behalf of the original signer. Proxy signatures are fundamentally accomplished by the process that original signer creates the signature about the proxy information and transmits to the proxy signer for using by the proxy key. There are several security requirements for using the proxy signature schemes. In this paper we suggest the proxy-register protocol scheme that original signer registers to the verifier about the proxy related information. In our scheme, verifier verifies the signature that original signer creates about the proxy information and sets the warrant of proxy signer, validity period for proxy signature and some limitation. At the same time, all security requirements that were mentioned in previous schemes are satisfied. We also show the advantages of our suggestion by comparing with the previous proxy signature schemes.

Generalization of proxy signature based on elliptic curves

In the past, proxy signature schemes were usually proposed to deal with one or two separate proxy conditions each. To make a difference, in this paper, the authors shall present a generalized version of proxy signature scheme. Compared to earlier proxy signature schemes, our novel scheme can be applied to every possible proxy situation. The proposed scheme allows the original group of original signers to delegate their signing capability to a designated proxy group. The proxy group of proxy signers can cooperatively generate a proxy signature on behalf of the original group. Any verifier can verify the proxy signature on the message with the knowledge of the identities of the actual original signers and the actual proxy signers. With this article, we also aim to demonstrate how to specify proxy signature schemes on elliptic curve over finite fields. In addition, some possible attacks have also been considered, and our security analysis will show that none of them can successfully break the proposed scheme.

Generalization of proxy signature-based on discrete logarithms

In the past few years, many excellent studies on proxy signature schemes have been published. Yet, traditional proxy signature schemes are mainly aimed at dealing with one or two separate proxy conditions each. In this article, the authors shall present a generalized version of the ( t 1/ n 1– t 2/ n 2) proxy signature scheme based on the discrete logarithms that can be applied to every proxy situation. The ( t 1/ n 1– t 2/ n 2) proxy signature scheme allows the original group of original signers to delegate their signing capability to a designated proxy group. The proxy group of proxy signers can cooperatively generate the proxy signature on behalf of the original group. Any verifier can verify the proxy signature on the message with the knowledge of the identities of the actual original signers and the actual proxy signers. Furthermore, some possible attacks have been considered, and our security analysis shows that none of them can successfully break the proposed scheme.

Design of time-stamped proxy signatures with traceable receivers

A proxy signature scheme is a method which allows an original signer to delegate his signing power to a proxy signer. Most proxy signature schemes use a warrant appearing in the signature verification equation to declare the valid delegation period. However, the declaration in the warrant is useless because no-one can know the exact time when the proxy signer signed a message. To avoid the proxy signer abusing the signing capability, the original signer may hope to know the identity of who received the proxy signature from the proxy signer. Recently Sun and Chen proposed the concept of time-stamped proxy signatures with traceable receivers to solve these two problems. A time-stamped proxy signature scheme with traceable receivers is a proxy signature scheme which can ascertain whether a proxy signature is created during the delegation period, and can trace who actually received the proxy signatures from the proxy signer. The author shows that Sun and Chen's scheme suffers from weaknesses and consequently proposes a new time-stamped proxy signature scheme which doesn't suffer from the same weaknesses.