Cipher block chaining (CBC) is a mode of operation for a block cipher. Cipher block chaining uses what is known as an initialization vector (IV) of a certain length.

 One of its key characteristics is that it uses a chaining mechanism that causes the decryption of a block of ciphertext to depend on all the preceding ciphertext blocks. As a result, the entire validity of all preceding blocks is contained in the immediately previous ciphertext block.

• A single bit error in a ciphertext block affects the decryption of all subsequent blocks. 
• Rearrangement of the order of the ciphertext blocks causes decryption to become corrupted. 
• Identical ciphertext blocks can only result if the same plaintext block is encrypted using the same key and the initialization vector, and if the ciphertext block order is not changed.

In this method, each plaintext block is XORed with the previous ciphertext block, and then encrypted.

Ideally, the initialization vector should be different for any two messages encrypted with the same key.

Though the initialization vector need not be secret, some applications may find this desirable.