Patent ID: 8798270

Claim:
A communication system including a first communication apparatus and a second communication apparatus as two communication apparatuses capable of encrypting transmission subject data using a predetermined algorithm in plain text to render it as encrypted data and then transmitting it to the communication apparatus at the other end and also decrypting received encrypted data and rendering it as the transmission subject data, wherein: both the first communication apparatus and the second communication apparatus comprise: cutting means for cutting the transmission subject data by a predetermined number of bits into multiple pieces of transmission subject cut data and also cutting the encrypted data into multiple pieces of encrypted cut data by the same number of bits by which the encrypted data is cut when encrypted; encrypting and decrypting means for encrypting the transmission subject cut data with the algorithm common between the first communication apparatus and the second communication apparatus to render it as the encrypted data and decrypting the encrypted cut data with the algorithm used when encrypting the encrypted cut data to render it as the transmission subject cut data; connecting means for connecting the decrypted transmission subject cut data to render it as the transmission subject data; and transmitting and receiving means for transmitting and receiving the encrypted data, and the cutting means cuts the transmission subject data so that at least one piece of the transmission subject cut data has a different number of bits from the other pieces of the transmission subject cut data, and wherein both the first communication apparatus and the second communication apparatus comprise: mixing means for including dummy data irrelevant to the transmission subject data in the transmission subject cut data except a transmission subject cut data with the largest number of bits thereof and thus matching the number of bits of every piece of the transmission subject cut data with the number of bits of the transmission subject data with the largest number of bits.