| 791 | Internet ProtocolJ. Postel | Internet Standard | September 1981 |
| 2560 | X.509 Internet Public Key Infrastructure Online Certificate Status Protocol - OCSPM. Myers, R. Ankney, A. Malpani, S. Galperin, C. Adams · obsoleted by RFC 6960 | Proposed Standard | June 1999 |
| 2818 | HTTP Over TLSE. Rescorla · obsoleted by RFC 9110 | Informational | May 2000 |
| 3261 | SIP: Session Initiation ProtocolJ. Rosenberg, H. Schulzrinne, G. Camarillo, A. Johnston, J. Peterson, R. Sparks, M. Handley, E. Schooler | Proposed Standard | July 2002 |
| 3263 | Session Initiation Protocol (SIP): Locating SIP ServersJ. Rosenberg, H. Schulzrinne | Proposed Standard | July 2002 |
| 3370 | Cryptographic Message Syntax (CMS) AlgorithmsR. Housley | Proposed Standard | September 2002 |
| 3428 | Session Initiation Protocol (SIP) Extension for Instant MessagingB. Campbell, Ed., J. Rosenberg, H. Schulzrinne, C. Huitema, D. Gurle | Proposed Standard | December 2002 |
| 3853 | S/MIME Advanced Encryption Standard (AES) Requirement for the Session Initiation Protocol (SIP)J. Peterson | Proposed Standard | July 2004 |
| 4134 | Examples of S/MIME MessagesP. Hoffman, Ed. | Informational | July 2005 |
| 4474 | Enhancements for Authenticated Identity Management in the Session Initiation Protocol (SIP)J. Peterson, C. Jennings · obsoleted by RFC 8224 | Proposed Standard | August 2006 |
| 4475 | Session Initiation Protocol (SIP) Torture Test MessagesR. Sparks, Ed., A. Hawrylyshen, A. Johnston, J. Rosenberg, H. Schulzrinne | Informational | May 2006 |
| 4514 | Lightweight Directory Access Protocol (LDAP): String Representation of Distinguished NamesK. Zeilenga, Ed. | Proposed Standard | June 2006 |
| 5055 | Server-Based Certificate Validation Protocol (SCVP)T. Freeman, R. Housley, A. Malpani, D. Cooper, W. Polk | Proposed Standard | December 2007 |
| 5246 | The Transport Layer Security (TLS) Protocol Version 1.2T. Dierks, E. Rescorla · obsoleted by RFC 8446, RFC 9846 | Proposed Standard | August 2008 |
| 5280 | Internet X.509 Public Key Infrastructure Certificate and Certificate Revocation List (CRL) ProfileD. Cooper, S. Santesson, S. Farrell, S. Boeyen, R. Housley, W. Polk | Proposed Standard | May 2008 |
| 5621 | Message Body Handling in the Session Initiation Protocol (SIP)G. Camarillo | Proposed Standard | September 2009 |
| 5652 | Cryptographic Message Syntax (CMS)R. Housley | Internet Standard | September 2009 |
| 5741 | RFC Streams, Headers, and BoilerplatesL. Daigle, Ed., O. Kolkman, Ed., IAB · obsoleted by RFC 7841 | Informational | December 2009 |
| 5751 | Secure/Multipurpose Internet Mail Extensions (S/MIME) Version 3.2 Message SpecificationB. Ramsdell, S. Turner · obsoleted by RFC 8551 | Proposed Standard | January 2010 |
| 5922 | Domain Certificates in the Session Initiation Protocol (SIP)V. Gurbani, S. Lawrence, A. Jeffrey | Proposed Standard | June 2010 |
| 5923 | Connection Reuse in the Session Initiation Protocol (SIP)V. Gurbani, Ed., R. Mahy, B. Tate | Proposed Standard | June 2010 |
| 5924 | Extended Key Usage (EKU) for Session Initiation Protocol (SIP) X.509 CertificatesS. Lawrence, V. Gurbani | Experimental | June 2010 |