With each plaintext block encryption, the adjacent ciphertext block must be used - like a chain. This means that the encryption of the plaintext block after the first one is dependent on the encryption of the first plaintext block. The only difference, however, is that the ciphertext block replaces the IV as one of the XOR inputs. This XOR output is then encrypted using a cipher key to produce a ciphertext block, an encrypted text format that can be decrypted with the correct key.įor example, after the first plaintext block has been transformed into a ciphertext block, the subsequent plaintext block must be encrypted using a similar process. The first step to initiating a cipher block chain is to XOR the first of many plaintext blocks with an IV - a unique, fixed-length conversion function - to create a random, or pseudorandom, output. Cipher block chaining is a cryptographic method used for turning plaintext into ciphertext and back again.Ĭipher block chaining is a process used to encrypt and decrypt large plaintext inputs by creating a cryptographic chain wherein each ciphertext block is dependent on the last.

The process repeats itself until all plaintext blocks have been successfully turned into ciphertext blocks. It is used in this case to facilitate the combination of plaintext blocks and encryption keys. An XOR is a coding mechanism used to combine different inputs. Rearrangement of the order of the ciphertext blocks, for example, can cause the decryption process to become corrupted.Įssentially, in cipher block chaining, each plaintext block is XORed (numerically combined) with the previous ciphertext block and then encrypted. A single bit error in a ciphertext block affects the decryption of all subsequent blocks. As a result, the entire validity of all preceding blocks is contained in the previous, adjacent ciphertext block. One of CBC's key characteristics is that it uses a chaining process that causes the decryption of a block of ciphertext to depend on all the preceding ciphertext blocks. By using this along with a single encryption key, organizations and individuals can safely encrypt and decrypt large amounts of plaintext. Cipher block chaining uses what is known as an initialization vector ( IV) of a certain length. Cipher block chaining (CBC) is a mode of operation for a block cipher - one in which a sequence of bits are encrypted as a single unit, or block, with a cipher key applied to the entire block.

Block cipher