What mode is known for creating a synchronous stream cipher using a block cipher?

The mode known for creating a synchronous stream cipher using a block cipher is the output feedback (OFB) mode. In OFB mode, the block cipher is used to generate keystream bits that are then XORed with the plaintext to produce ciphertext. This process effectively turns the block cipher into a synchronous stream cipher since the keystream can be generated independently of the plaintext and does not depend on the ciphertext.

OFB continuously feeds back the output of the block cipher into the encryption algorithm, which allows it to produce an arbitrary length of keystream, matching the length of the input data. This decoupling of the encryption of the plaintext from the initialization vector and ciphertext means that OFB can operate similarly to a stream cipher, making it suitable for applications requiring real-time encryption.

In contrast, the other modes mentioned, such as cipher feedback (CFB), cipher-block chaining (CBC), and electronic codebook (ECB), do not function in the same manner as OFB for creating a synchronous stream cipher. CFB, while it also can produce a stream of output, is inherently more reactive to changes in the ciphertext; CBC relies on feedback from the preceding ciphertext block and requires the entire block to be processed sequentially, which does not