Final answer:
The process in which a ciphertext block is encrypted and then XOR'd with the plaintext to produce the current ciphertext block is known as Cipher-block chaining (CBC). It ensures that the same plaintext block will produce different ciphertext blocks in different parts of the message.
Step-by-step explanation:
The process described in the question is known as Cipher-block chaining (CBC). In this mode of operation, each plaintext block is XOR'd (exclusive OR) with the previous ciphertext block before being encrypted. This method enhances security by incorporating a chain of dependencies among the ciphertext blocks. Because of this chaining, the same block of plaintext will result in a different ciphertext block every time it is encrypted, provided the previous ciphertext block is different.
In contrast, Output feedback (OFB) and Cipher feedback (CFB) modes also use feedback for encryption, but they work somewhat differently. In OFB, the previous output is encrypted to become the keystream, which is then XOR'd with the plaintext, while in CFB, the previous ciphertext block is encrypted and then XOR'd with the plaintext to produce the next block of ciphertext. Electronic codebook (ECB) mode is the simplest form of encryption that treats each block independently without any chaining.