M. Myers, R. Ankney, A. Malpani, S. Galperin, <a href="http://www.ietf.org/rfc/rfc2560.txt"> <cite>X.509 Internet Public Key Infrastructure Online Certificate Status Protocol - OCSP</cite> </a>.  C. Adams. IETF RFC 2560. June 1999. URL: <a href="http://www.ietf.org/rfc/rfc2560.txt">http://www.ietf.org/rfc/rfc2560.txt</a>