References

   [1] CCITT Recommendation X.411 (1988), "Message Handling Systems:
       Message Transfer System: Abstract Service Definition and
       Procedures".

   [2] CCITT Recommendation X.509 (1988), "The Directory -
       Authentication Framework".

   [3] CCITT Recommendation X.520 (1988), "The Directory - Selected
       Attribute Types".

   [4] NIST Special Publication 500-183, "Stable Agreements for Open
       Systems Interconnection Protocols," Version 4, Edition 1,
       December 1990.

   [5] North American Directory Forum, "A Naming Scheme for c=US", RFC
       1255, NADF, September 1991.

   [6] Linn, J., "Privacy Enhancement for Internet Electronic Mail: Part
       I: Message Encryption and Authentication Procedures", RFC 1421,
       DEC, February 1993.

   [7] Balenson, D., "Privacy Enhancement for Internet Electronic Mail:
       Part III: Algorithms, Modes, and Identifiers", RFC 1423, TIS,
       February 1993.

   [8] Balaski, B., "Privacy Enhancement for Internet Electronic Mail:
       Part IV: Notary, Co-Issuer, CRL-Storing and CRL-Retrieving
       Services", RFC 1424, RSA Laboratories, February 1993.
   [9] North American Directory Forum, "NADF Standing Documents: A Brief
       Overview", RFC 1417, NADF, February 1993.