Final answer:
Stream ciphers use a key stream to encrypt and decrypt a plaintext message. They differ from transposition and substitution ciphers, which work on rearranging blocks of text or replacing elements of plaintext, respectively.
Step-by-step explanation:
The type of ciphers that use a key stream to encrypt and decrypt a plaintext message are stream ciphers. In cryptography, a stream cipher is a symmetric key cipher where plaintext digits are combined with a pseudorandom cipher digit stream (key stream). Each plaintext digit is encrypted one at a time with the corresponding digit of the key stream, to give a digit of the ciphertext stream. Unlike substitution ciphers or transposition ciphers, which encrypt elements of the plaintext in blocks, stream ciphers work on a single element at a time (typically single bits or bytes).
Understanding the context in which different ciphers are used, such as the transposition cipher used in the Zimmerman Telegram, helps to highlight the uniqueness of each encryption method. In a transposition cipher, the letters of the plaintext are shuffled according to a systematic method, but the letters themselves remain unchanged. This is different from the keystream method used by stream ciphers, where a key is used to encrypt each bit or byte of plaintext individually.