The coding machine added together the "plaintext" (the un-coded version of the message) and a stream of characters (letters, numbers, punctuation) called the "keystream" (a stream of seemingly random characters) that it generated to make the "ciphertext" (the coded version of the message). The ciphertext, which made no sense, was transmitted by radio. At the receiving end an identical machine removed the keystream to produce the plaintext of the message.