1. CCITT: Blue Book Directory, Recommendations X.500-X.521 (1988). Geneva, 1989. (see also: ISO 9594)
2. Friedrich L Bauer. Kryptologie, Methoden und Maximen, Springer (1993)
3. John Linn. Privacy Enhancement for Internet Electronic Mail: Part I: Message Encryption and Authentication Procedures. RFC 1421 Stephen Kent. Privacy Enhancemet for Internet Electronic Mail: Part II: Certificate Based Key Management. RFC 1422 David Balenson. Privacy Enhancement for Internet Electronic Mail: Part III: Algorithms, Modes and Identifiers. RFC 1423 B. Kaliski. Privacy Enhancement for Internet Electronic Mail: Part IV: Key Certification and Related Services. RFC 1424
4. PASSWORD: see
http://www.darmstadt.gmd.de/TKT/gmdda.tk.pr5.html
5. Wolfgang Schneider. SecuDE, Overview Version 4.1 (1993) GMD, Institut für TeleKooperations Technik (12), Darmstadt, Germany