AES-128 encryption and decryption overview

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2.2

Cipher Block Chaining (CBC)

The Cipher Block Chaining mode allows an higher level of entropy because the output of the

first ciphertext is derived by an initialization vector and a cryptographic key.

The chaining structure permits using the previous ciphertext as cryptographic key for the

next encryption block, as described in Figure 3.

Using this mode, each cipher block depends on the previous processed plaintext block.

Figure 3. CBC block diagram

2.3

CMAC (Cipherbased Message Authentication Code)

A CMAC provides a method for authenticating messages and data. The CMAC algorithm

accepts as input a secret key and an arbitrary-length message to be authenticated, and

outputs a CMAC. The CMAC value protects both a message's data integrity as well as its

authenticity, by allowing verifiers (who also possess the secret key) to detect any change in

the message content.

Figure 4. CMAC Scheme