Buffered cyphering

Encryption and decryption mechanisms at transmitters and receivers, respectively, have applied thereto encryption or decryption keys and initialising values. These mechanisms generate cryptographic bit streams which are intermediate streams of generated values. These intermediate streams, generated prior to their real time need in the encryption or decryption processes, are stored in buffers until data is presented for encryption or decryption, at which time the cryptographic bit streams are conveyed from the buffers to mathematical functions, for combination with the data. This avoids the delays associated with the real time generation of the cryptographic bit streams during the encryption and decryption processes. Appropriate synchronisation of the generation and buffer storage of the cryptographic bit streams at the transmitter and receiver is provided.