Group-Oriented Undeniable Signature Scheme for Unlikely Signers and Verifiers

• Main Authors: Hao-Chih Liao, 廖浩志
• Other Authors: Shin-Jia Hwang
• Format: Others
• Language: en_US
• Published: 2004
• Online Access: http://ndltd.ncl.edu.tw/handle/37835899028218563799

碩士 === 淡江大學 === 資訊工程學系 === 92 === Digital signatures provides the authentication and non-repudiation services. However, digital signatures can be easily transmitted to unauthorized ones. To overcome this problem, the concept of undeniable signatures is proposed by Chaum and van Antwerpen. Moreover, some group-oriented undeniable signatures schemes are proposed for group-oriented applications. However, these schemes are not secure against Langford’s attack. To protect against Langford’s attack, Lee and Hwang proposed their group-oriented undeniable signature schemes with a trusted center. Unfortunately, there are some security weaknesses in Lee-Hwang’s schemes. In their scheme, the signers and verifier must be assumed to honestly perform any steps; otherwise their scheme will fail. To remove this impractical honest member assumption and the corresponding problems, an improved group-oriented undeniable scheme is proposed. In Hsu-Wu’s authenticated encryption scheme with threshold shared verification, there is the same assumption that all verifiers in the verifier group honestly execute the decryption process to recovery the message m. However, in practical application, it is hard to trust that all the members in the verifier group are honest. When some malicious members exist in the receiving group, two possible attacks are proposed to break Hsu-Wu’s scheme. One is an intercepts attack and one is counterfeit commit value attack.