Cryptology ePrint Archive: Report 2005/041

On the Security of a Group Signature Scheme with Strong Separability

Lihua Liu and Zhengjun Cao

Abstract: A group signature scheme allows a group member of a given group to sign messages on behalf of the group in an anonymous and unlinkable fashion. In case of a dispute, however, a designated group manager can reveal the signer of a valid group signature. Many applications of group signatures require that the group manager can be split into a membership manager and a revocation manager. Such a group signature scheme with strong separability was proposed in paper [1]. Unfortunately, the scheme is insecure which has been shown in [2][3][4]. In this paper we show that the scheme is untraceable by a simple and direct attack. Besides, we show its universal forgeability by a general attack which only needs to choose five random numbers. We minutely explain the technique to shun the challenge in the scheme.

Category / Keywords: cryptographic protocols / Group signature, Untraceability,Universal forgeability.

Date: received 15 Feb 2005

Contact author: zjcamss at hotmail com

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Version: 20050216:155505 (All versions of this report)

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