## CryptoDB

### Yodai Watanabe

#### Publications

Year
Venue
Title
2004
EPRINT
This paper considers a weak variant on the notion of zero-knowledge. The weak notion is compatible with the chosen ciphertext security. In fact, arguments of knowledge based on IND-CCA encryption schemes are shown to be statistical zero-knowledge in that sense.
2003
PKC
2003
EPRINT
This paper studies the relation among simulator-based and comparison-based definitions of semantic security. The definitions are considered in a more general framework than the ordinal one; namely, an adversary is assumed to have access to prior information of a plaintext. If the framework is restricted to the ordinal one, then all the security notions considered in this paper, including indistinguishability, are shown to be equivalent. On the other hand, the equivalence is not necessarily valid in the general framework. In fact, it is shown that no encryption scheme is secure in the sense of comparison-based semantic security in the strongest forms. Furthermore, a sufficient condition for the equivalence between semantic security and indistinguishability is derived.
2002
EPRINT
The aim of this work is to examine the relation between the notions of semantic security and indistinguishability against chosen ciphertext attacks. For this purpose, a new security notion called non-dividability is introduced independent of attack models, and is shown to be equivalent to both of the two notions. This result is expected to provide a clearer understanding of the equivalence between semantic security and indistinguishability under any form of attack.

#### Coauthors

Hideki Imai (2)
Junji Shikata (3)