Information Transfer security labels convey information used by protocol entities to determine how to handle data communicated between open systems. Information on a security label can be used to control access, specify protective measures, and determine handling restrictions required by a communications security policy. This standard defines a security label syntax for information exchanged over data networks and provides encodings of that syntax for use at the Application and Network Layers. The syntactic constructs defined in this standard are intended to be used along with semantics provided by the authority establishing the security policy for the protection of the information exchanged. A separate NIST document, referenced in an informative appendix, defines a Computer Security Objects Register (CSOR) that serves as repository for label semantics.