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Scope and field of application

This International Standard applies to systems for encipherment of ADP information in the physical layer of data communications.

This International Standard is equally applicable whether the Data Encipherment Equipment (DEE) is implemented as a physically separate piece of equipment or implemented as part of the Data Terminal Equipment (DTE) or as part of the Data Circuit terminating Equipment (DCE). When the encipherment is integrated into the DTE or DCE, this International Standard applies to those portions of the DTE or DCE design which implement the requirements of this International Standard. Interoperability requirements are defined for the following physical interface definitions: V.24, X.20 bis, X.21 bis, X.20, and X.21.

The physical layer is described in the Open Systems Interconnectio n Reference Model, ISO 7498. In physical layer encipherment, all of the SDU is normally enciphered. The interoperability requirements described in this International Standard apply to both synchronous and asynchronous operation in both full duplex and half duplex modes.

The main body of this International Standard specifies requirements which are applicable to the use of various encipherment algorithms. Annex B Specifies additional requirements for the use of DEA (ANSI X3.92-1981).

This International Standard also specifies two alternative modes of synchronous operation - the delayed option and the immediate option - which are mutually incompatible.

This International Standard also specifies two alternative actions for BREAK signalling for asynchronous operation - Class A and Class B - which are mutually incompatible.