D. Cooper, et. al. <a href="http://www.ietf.org/rfc/rfc5280.txt"><cite> Internet X.509 Public Key Infrastructure Certificate and Certificate Revocation List (CRL) Profile. </cite></a>. IETF RFC 5280 May 2008. URL: <a href="http://www.ietf.org/rfc/rfc5280.txt">http://www.ietf.org/rfc/rfc5280.txt</a>