A cipher device (or cipher machine, cipher box, crypto box) is a physical cryptographic device used to encrypt and decrypt messages between plaintext (unencrypted) and ciphertext (encrypted or secret) forms. The ciphertext is suitable for transmission over a channel, such as radio, that might be observed by an adversary the communicating parties wish to conceal the plaintext from.
Mechanical[disambiguation needed] and electromechanical devices have been used as cipher devices, but modern implementations are digital devices.