A software developer is setting up a symmetric encryption block cipher with an initial chaining vector. Which will they use?

In symmetric encryption, especially when using block ciphers, the term "initial chaining vector" refers to the method of incorporating an initialization vector (IV) into the encryption process to ensure that the same plaintext encrypted multiple times produces different ciphertexts. This is crucial in maintaining the confidentiality of the encrypted data.

The correct choice involves a mode of operation that effectively utilizes an IV. In this case, Cipher Block Chaining (CBC) mode is specifically designed to work with an initialization vector. CBC mode ensures that each block of plaintext is XORed with the previous block of ciphertext before being encrypted, which makes it highly secure against patterns over multiple encryptions as it relies on the IV to kick-start the encryption process.

Other modes like CTR (Counter) and OFB (Output Feedback) also use IVs but operate differently than CBC. CTR turns the block cipher into a stream cipher by generating a key stream based on the counter and the IV, while OFB generates a stream of key material before processing the plaintext but does not provide the same level of chaining between blocks as CBC does. Triple DES (3DES) is a specific encryption algorithm but is not a mode of operation; it can use CBC but does not inherently include a method for using an IV.