Traceability Schemes against Illegal Distribution of Signed Documents

Shoko YONEZAWA  Goichiro HANAOKA  Junji SHIKATA  Hideki IMAI  

IEICE TRANSACTIONS on Fundamentals of Electronics, Communications and Computer Sciences   Vol.E87-A    No.5    pp.1172-1182
Publication Date: 2004/05/01
Online ISSN: 
Print ISSN: 0916-8508
Type of Manuscript: Special Section LETTER (Special Section on Discrete Mathematics and Its Applications)
signed document,  illegal distribution,  traceability,  group signature,  partially blind signature,  

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Illegal distribution of signed documents can be considered as one of serious problems of digital signatures. In this paper, to solve the problem, we propose three protocols concerning signature schemes. These schemes achieve not only traceability of an illegal user but also universal verifiability. The first scheme is a basic scheme which can trace an illegal receiver, and the generation and tracing of a signed document are simple and efficient. However, in this scheme, it is assumed that a signer is honest. The second scheme gives another tracing method which does not always assume that a signer is honest. Furthermore, in the method, an illegal user can be traced by an authority itself, hence, it is efficient in terms of communication costs. However, in this scheme it is assumed that there exists only a legal verification algorithm. Thus, in general, this scheme cannot trace a modified signed document which is accepted by a modified verification algorithm. The third one is a scheme which requires no trusted signer and allows a modified verification algorithm. It can trace an illegal receiver or even a signer in such a situation. All of our schemes are constructed by simple combinations of standard signature schemes, consequently, one can flexibly choose suitable building blocks for satisfying requirements for a system.