59.4 Functional Description

The Advanced Encryption Standard Bridge (AESB) specifies a FIPS-approved cryptographic algorithm that can be used to protect electronic data. The AESB algorithm is a symmetric block cipher that can encrypt (encipher) and decrypt (decipher) information.

Encryption converts data to an unintelligible form called ciphertext. Decrypting the ciphertext converts the data back into its original form, called plaintext. CIPHER in the AESB Mode register (AESB_MR) allows selection between the encryption and the decryption processes.

The AESB is capable of using cryptographic keys of 128 bits to encrypt and decrypt data in blocks of 128 bits. This 128-bit key is defined in the Key registers (AESB_KEYWRx).

The input to the encryption processes of the CBC mode includes, in addition to the plaintext, a 128-bit data block called the initialization vector (IV), which must be set in the Initialization Vector Registers (AESB_IVRx). The initialization vector is used in an initial step in the encryption of a message and in the corresponding decryption of the message. The Initialization Vector registers are also used by the CTR mode to set the counter value.