CIPHER COMMUNICATION SYSTEM

摘要

PROBLEM TO BE SOLVED: To provide a cipher communication system which makes it difficult for the third person to estimate a secret key by an attack and can reduce an influence upon the system in the case that the secret key is decoded. SOLUTION: In the cipher communication system consisting of 28 one transmission equipment 10 and reception equipments A1 to G4 in total which are classified into seven groups A to G, two secret keys which are selected from 14 kinds of secret keys without duplication are preliminarily delivered t each group. The transmission equipment 10 uses either of two secret keys delivered to each group to cipher the same message M and transmits it to reception equipments in the corresponding group. Each reception equipment uses two secret keys delivered to the group, to which the reception equipment belongs, to decipher a received cipher text and discriminates whether two obtained deciphered texts meet certain regularity respectively or not, thereby specifying a correct deciphered text.