[Originally published as Federal Standard 2016 (FED-STD-1026) by the General Services Administration, prepared by the National Communications System. Note on Cover: "Federal Standard 1026 has been redesignated as Federal Information Processing Standards publication (FIPS PUB) 139."]

This standard specifies interoperability and security related requirements for using encryption at the Physical Layer of the ISO Open Systems Interconnection (OSI) Reference Model in telecommunication systems conveying Automatic Data Processing (ADP) and/or narrative text information. The algorithm used for encryption is the Data Encryption Standard (DES), described in Federal Information Processing Standards Publication 46. Requirements contained in this standard relate to the interoperation of Physical Layer Data Encryption Equipment, or their interoperation with associated Data Terminal Equipment or Data Circuit-terminating Equipment. Additional security requirements, not directly relating to interoperability, are contained in Federal Standard 1027.