A Short Verifier-Local Revocation Group Signature Scheme with Backward Unlinkability

Toru NAKANISHI  Nobuo FUNABIKI  

Publication
IEICE TRANSACTIONS on Fundamentals of Electronics, Communications and Computer Sciences   Vol.E90-A   No.9   pp.1793-1802
Publication Date: 2007/09/01
Online ISSN: 1745-1337
DOI: 10.1093/ietfec/e90-a.9.1793
Print ISSN: 0916-8508
Type of Manuscript: Special Section PAPER (Special Section on Information Theory and Its Applications)
Category: 
Keyword: 
group signature,  revocation,  backward unlinkability,  bilinear maps,  DLDH assumption,  

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Summary: 
Previously Verifier-Local Revocation (VLR) group signature schemes from bilinear maps were proposed. In VLR schemes, only verifiers are involved in the revocation of a member, while signers are not. Thus, the VLR schemes are suitable for mobile environments. Furthermore, the previously proposed schemes satisfy the important backward unlinkability. This means that even after a member is revoked, signatures produced by the member before the revocation remain anonymous. This property is needed in case of a voluntary leave of a member or in case of a key loss. However, in the previous schemes, signatures become long, due to the adopted assumption, which should be improved in order to apply the schemes to the mobile environments. In this paper an improved VLR scheme is proposed with the shorter group signatures. This is achieved by using a different assumption, DLDH assumption, and improving zero-knowledge proofs in the group signatures. The length of the proposed group signatures is reduced to about 53% of that of the previous ones.