Cryptlib X.509 v.3 Certificates : S/MIME & SSL Client/Server Certificates - http://www.cryptlib.com/
Cryptlib frovides full support for X.509 v.3 Certificates, including S/MIME & SSL Client/Server Certificates, SET certificates, Microsoft AuthentiCode, Netscape server-gated crypto certificates, Identrus, and Thawte secure extranet