Defines interoperability and security related requirements for using encipherment at the physical layer of the ISO Open Systems Interconnection (OSI) Reference Model in telecommunication systems conveying Automatic Data Processing (ADP) information. Facilitates interoperation of data encipherment equipment. Applicable mainly to various encipherment algorithms. Annex B provides additional requirements for using DEA and applies to synchronous and asynchronous operation in full and half duplex modes. Specifies delayed option and immediate option als incompatible modes of synchronous operation.