Abstract: Communications security between a host computer and another remote computer or terminal is ensured by a means of a two-tiered cryptographic communications security device and procedure. A master key is used to encrypt a first session key. The session key encrypted under the master key is transmitted from a remote facility to a host computer. At the host computer, the session key is decrypted and stored, a second and different session key is then generated, encrypted under the master key and transmitted to the remote facility where it is utilized as the facilities session decryptor key. Because the session key utilized for transmission of data between the remote facility and the host differs from the session key utilized for transmission of data between the host and the remote facility, communications security is increased.