ITU X.509 Authentication Framework Draft Early draft of the ITU X.509 recommendation. (German National Research Center for Information Technology) ftp://ftp.darmstadt.gmd.de/pub/secude/standards/x509v3/

Digital ID Introduction Introductory level overview of digital certificates. http://digitalid.verisign.com/client/help/id_intro.htm

Handbook of Applied Cryptography Introduction to the practical aspects of conventional and public-key cryptography. (PDF and Postscript sample chapters) http://www.cacr.math.uwaterloo.ca/hac/

An Internet AttributeCertificate Profile for Authorization This PKIX draft defines two profiles for the use of X.509 AttributeCertificates to provide authorization support for protocols like TLS, CMS and their consumers, and others. http://www.ietf.org/internet-drafts/draft-ietf-pkix-ac509prof-09.txt