Patent Number: 6,307,940

Title: Communication network for encrypting/deciphering communication text while updating encryption key, a communication terminal thereof, and a communication method thereof

Abstract: In a cryptosystem which performs encryption/deciphering of communication text using k bits of cryptographically secure pseudo-random numbers as the block cipher key thereof, the block cipher key is updated each time j=k/m bits of new pseudo-random numbers are generated, with the j.multidot.m=k bits of pseudo-random numbers created by combining the j.multidot.(m-1) bits within the k bits of the present key and the newly generated j bits, serving as a new key, thereby shortening the updating cycle and improving the safety. Also, by sending the number of times of generation of pseudo-random numbers along with the encrypted communication text from the sending side, and by the receiving side using from the sequentially generated pseudo-random numbers, pseudo-random numbers generated after the received number of times of generation as the new key, deciphering can be performed regardless of the order to reception, in the event that a plurality of cipher texts are sequentially sent while updating the encryption key.

Inventors: Yamamoto; Takahisa (Kawasaki, JP), Iwamura; Keiichi (Yokohama, JP)

Assignee: Canon Kabushiki Kaisha

International Classification: H04L 9/18 (20060101); H04L 9/22 (20060101); H04L 009/00 ()

Expiration Date: 10/23/2018