ENCRYPTION APPARATUS, COMMUNICATION SYSTEM USING THE SAME AND METHOD THEREFOR

In order to attain high speed and secure encryption, a communication apparatus comprises a random number generation circuit for sequentially generating random number sequences which assure difficulty in terms of amount of calculation in cryptoanalyzing the sequences based on output sequences while using a cryptographic key shared by partner stations as an initial value, and an encryption circuit for sequentially encrypting communication texts and outputting cryptograms in a transmitting station and sequentially cryptoanalyzing the cryptograms and outputting the same in a receiving station, faster than the sequential generation of the random numbers by the random number generation circuit.