CBC

Cipher block chaining or CBC, is a mode in which a sequence of bits are encrypted as a single unit or a block. When encrypted as a block, a cipher key is applied to the entire sequence. Cipher block chaining uses an IV (initialization vector) of a specific length. One of it’s characteristics is a chaining mechanism that forces the decryption of ciphertext to rely on preceding ciphertext blocks. This means that the validity of all preceding blocks are contained in the previous block. An error pertaining to a single bit then has the ability to effect the decryption of all subsequent ciphertext blocks. CBC only allows the creation of identical ciphertext blocks if the same plaintext block has been encrypted using the same key and IV. This may also be permitted if the order of the ciphertext block has not been modified. Any modifications applied to a ciphertext block should be done with caution as rearrangement corrupts the decryption process.