Encryption apparatus

Abstract

In an encryption apparatus, prior to encryption process, information indicating whether plain text blocks are to be encrypted or not is stored in a mask register, and the number of blocks of the plain text block sequence is stored in a count register. In the encryption process, the count register is sequentially decremented, and only the plain text blocks to be encrypted are read from an input buffer in an ascending order of addresses based on the information stored in the mask register. They are encrypted by an encryption circuit and the encrypted text blocks are stored in an output buffer at the corresponding addresses to the input buffer addresses at which the plain text blocks have been stored. After the encryption process for the plain text blocks to be encrypted, only the plain text blocks not to be encrypted are sequentially read from the input buffer in the ascending order of the addresses and they are stored, without being encrypted, in the output buffer at the corresponding addresses to the input buffer addresses at which the plain text blocks have been stored.

Dependencies are inferred from the claim text.