key

…marks and spaces (a running key) were mingled with the message during encryption to produce what is known as a stream or streaming cipher.

…believed that a short random key could safely be reused many times, thus justifying the effort to deliver such a large key, but reuse of the key turned out to be vulnerable to attack by methods of the type devised by Friedrich W. Kasiski, a 19th-century German army officer and…

A personal encryption key, or name, known only to the transmitter of the message and its intended receiver, is used to control the algorithm’s encryption of the data, thus yielding unique ciphertext that can be decrypted only by using the key.

…the legitimate users is the key, and the transformation of the plaintext under the control of the key into a cipher (also called ciphertext) is referred to as encryption. The inverse operation, by which a legitimate receiver recovers the concealed information from the cipher using the key, is known as…