Patent ID: 8908859

Claim:
A cryptographic apparatus, comprising: a plurality of cryptographic processing circuits, each of which includes a flag storage unit that stores therein a CipherText Stealing (CTS) flag indicating whether an encryption that utilizes CTS is to be performed, and each of which operates in a same predetermined block cipher mode of operation and performs, when the CTS flag thereof is turned on, a complete encryption using a symmetric key cipher algorithm that utilizes CTS, while using a symmetric key; an assigning unit configured to receive an input of a CTS signal indicating that second input data, that is input immediately after first input data having a block length, is shorter than the block length, to assign the first input data to one of the plurality of cryptographic processing circuits and to turn on the CTS flag of the one of the cryptographic processing circuits to which the first input data is assigned; a concatenating unit that generates concatenated data by concatenating operation data generated during encrypting the first input data at the one of the cryptographic processing circuits and the second input data; an output controlling unit that controls outputting the concatenated data to the one of the cryptographic processing circuits at which the first input data was encrypted, controls outputting first encrypted data obtained by encrypting the concatenated data at the one of the cryptographic processing circuits, and controls outputting second encrypted data obtained by encrypting the first input data at the one of the cryptographic processing circuits, and turns off the CTS flag of the one of the cryptographic processing circuits; and a single register that stores the second input data while the one of the cryptographic processing circuits, operating in the predetermined block cipher mode, completely encrypts the first input data, wherein the single register stores the second encrypted data while the one of the cryptographic processing circuits, operating in the predetermined block cipher mode, completely encrypts the concatenated data.