Atsuhiro Yamagishi

A new method for known plaintext attack of FEAL cipher

We propose a new known plaintext attack of FEAL cipher. Our method differs from previous statistical ones in point of deriving the extended key in definite way. As a result, it is possible to break FEAL-4 with 5 known plaintexts and FEAL-6 with 100 known plaintexts respectively. Moreover, we show a method to break FEAL-8 with 215 known plaintexts faster than an exhaustive search.

An improved identity-based one-way conference key sharing system

For communication among multiple entities, Chikazawa, and Inoue (1990) published an identity-based one-way key sharing system. However, Simbo and Kawamura (1991) developed an attack which can derive the secret information of entities through a conspiracy of other entities in the system. The present authors propose an improved identity-based one-way conference key sharing system to counter their attack by giving entities unique random numbers.<<ETX>>