Which block cipher mode of operation uses a nonce combined with a counter that is encrypted?

Counter Mode (CTR) is a block cipher mode of operation that effectively utilizes a nonce (number used once) combined with a counter to create a unique encryption sequence for each block of plaintext. In CTR mode, the encryption process consists of taking a nonce and a counter value, encrypting this combination, and then XORing the result with the plaintext to produce the ciphertext. This method ensures that even if the same plaintext block is encrypted multiple times, the ciphertext will be different each time due to the changing counter value.

The use of a nonce and a counter in CTR mode also allows for parallel processing of the blocks, improving performance and efficiency in encryption and decryption tasks. This makes CTR particularly suitable for environments where speed is essential and where the same plaintext might need to be encrypted multiple times without risk of generating the same ciphertext.

In contrast, the other modes mentioned—Electronic Code Book (ECB), Cipher Block Chaining (CBC), and Cipher Feedback Mode (CFB)—do not operate using a nonce and counter in the same manner that CTR does. ECB, for example, encrypts each block independently without any chaining or variation, making it less secure for certain use cases. CBC relies on the chaining of blocks to provide security, while CFB