Alternative variants of zero-knowledge proofs
Zero-knowledge proofs are one of the most important cryptographic notions.
Since their introduction in the early 80's by Goldwasser, Micali and
Racko , they have proven very useful in the design of cryptographic protocols.
Nevertheless, many limitations (in terms of e ciency and robustness
under concurrent executability of protocols) have also been noticed. In order
to overcome these limitations two lines of research have been investigated in
1. Models with some limited intervention of a trusted party (for example
during a set-up phase).
2. Weakenings of the notion of zero-knowledge.
In this thesis we attempt to further the understanding of the notion of
zero-knowledge proofs by addressing both the above lines of research. More
1. Concerning the rst line of research, we show that the de nition of zeroknowledge
in certain popular models (namely the Common Reference
String and Random Oracle Models) captures a somewhat di erent semantics
than the standard zero-knowledge de nition. In particular, we
show that there exists a certain natural security property that is captured
by the standard de nition, but not by these new de nitions. This
between two parties does not leave any trace . We then focus on investigating
the possibility of obtaining deniable zero-knowledge protocols
in these models.
2. Concerning the second line of research, we propose a new and di erent
us to a) overcome known impossibility results concerning the notion
of zero-knowledge, while b) providing an almost as strong security
School:Kungliga Tekniska högskolan
Source Type:Master's Thesis
Keywords:MATHEMATICS; Applied mathematics; Theoretical computer science
Date of Publication:01/01/2004