http://www.rfc-editor.org/rfc/rfc4051.txt
RFC 4051: Additional XML Security Uniform Resource Identifiers (URIs), D. Eastlake 3rd2005-04-01T23:00:00-00:00A number of Uniform Resource Identifiers (URIs) intended for use with XML Digital Signatures, Encryption, and Canonicalization are defined. These URIs identify algorithms and types of keying information. [STANDARDS-TRACK]