



Internet Engineering Task Force (IETF)                        C. Lonvick
Request for Comments: 9662                                              
Updates: 5425, 6012                                            S. Turner
Category: Standards Track                                          sn3rd
ISSN: 2070-1721                                               J. Salowey
                                                                  Venafi
                                                            October 2024


             Updates to the Cipher Suites in Secure Syslog

Abstract

   RFCs 5425 and 6012 describe using TLS and DTLS to securely transport
   syslog messages.  This document updates the cipher suites required by
   RFC 5245 (TLS Transport Mapping for Syslog) and RFC 6012 (DTLS
   Transport Mapping for Syslog).  It also updates the protocol
   recommended by RFC 6012 for secure datagram transport.

Status of This Memo

   This is an Internet Standards Track document.

   This document is a product of the Internet Engineering Task Force
   (IETF).  It represents the consensus of the IETF community.  It has
   received public review and has been approved for publication by the
   Internet Engineering Steering Group (IESG).  Further information on
   Internet Standards is available in Section 2 of RFC 7841.

   Information about the current status of this document, any errata,
   and how to provide feedback on it may be obtained at
   https://www.rfc-editor.org/info/rfc9662.

Copyright Notice

   Copyright (c) 2024 IETF Trust and the persons identified as the
   document authors.  All rights reserved.

   This document is subject to BCP 78 and the IETF Trust's Legal
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   Trust Legal Provisions and are provided without warranty as described
   in the Revised BSD License.

Table of Contents

   1.  Introduction
   2.  Terminology
   3.  Support for Updating
   4.  Updates to RFC 5425
   5.  Updates to RFC 6012
   6.  Early Data
   7.  IANA Considerations
   8.  Security Considerations
   9.  References
     9.1.  Normative References
     9.2.  Informative References
   Acknowledgments
   Authors' Addresses

1.  Introduction

   "Transport Layer Security (TLS) Transport Mapping for Syslog"
   [RFC5425] and "Datagram Transport Layer Security (DTLS) Transport
   Mapping for Syslog" [RFC6012] describe using TLS and DTLS to securely
   transport syslog messages.  Both of these specifications require the
   use of RSA-based certificates and the use of TLS and DTLS versions
   that are not the most recent.

   Section 4.2 of [RFC5425] requires that implementations MUST support
   TLS 1.2 [RFC5246] and are REQUIRED to support the mandatory-to-
   implement cipher suite TLS_RSA_WITH_AES_128_CBC_SHA.

   Section 5.2 of [RFC6012] requires that implementations "MUST" support
   DTLS 1.0 [RFC4347] and are also "REQUIRED" to support the mandatory-
   to-implement cipher suite TLS_RSA_WITH_AES_128_CBC_SHA.

   The community is moving away from cipher suites that do not offer
   forward secrecy and towards more robust suites.

   The DTLS 1.0 transport [RFC4347] has been deprecated by RFC 8996
   [BCP195], and the community is moving to DTLS 1.2 [RFC6347] and DTLS
   1.3 [RFC9147].

   This document updates [RFC5425] and [RFC6012] to prefer the use of
   TLS_ECDHE_RSA_WITH_AES_128_GCM_SHA256 over the use of
   TLS_RSA_WITH_AES_128_CBC_SHA.

   This document also updates [RFC6012] by recommending a mandatory-to-
   implement secure datagram transport.

2.  Terminology

   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
   "SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and
   "OPTIONAL" in this document are to be interpreted as described in
   BCP 14 [RFC2119] [RFC8174] when, and only when, they appear in all
   capitals, as shown here.

3.  Support for Updating

   [RFC8447bis] generally reminds us that cryptographic algorithms and
   parameters will be broken or weakened over time.  Blindly
   implementing the cryptographic algorithms listed in any specification
   is not advised.  Implementers and users need to check that the
   cryptographic algorithms specified continue to provide the expected
   level of security.

   As the Syslog Working Group determined, syslog clients and servers
   MUST use certificates as defined in [RFC5280].  Since both [RFC5425]
   and [RFC6012] REQUIRED the use of TLS_RSA_WITH_AES_128_CBC_SHA, it is
   very likely that RSA certificates have been implemented in devices
   adhering to those specifications.  RFC 9325 [BCP195] notes that ECDHE
   cipher suites exist for both RSA and ECDSA certificates, so moving to
   an ECDHE cipher suite will not require replacing or moving away from
   any currently installed RSA-based certificates.

   [DEPRECATE-KEX] documents that the cipher suite
   TLS_RSA_WITH_AES_128_CBC_SHA, along with some other cipher suites,
   may require mitigation techniques to achieve expected security, which
   may be difficult to effectively implement.  Along those lines, RFC
   9325 [BCP195] notes that TLS_RSA_WITH_AES_128_CBC_SHA does not
   provide forward secrecy, a feature that is highly desirable in
   securing event messages.  That document also goes on to recommend
   TLS_ECDHE_RSA_WITH_AES_128_GCM_SHA256 as a cipher suite that does
   provide forward secrecy.

   As such, the community is moving away from algorithms that do not
   provide forward secrecy.  For example, the International
   Electrotechnical Commission (IEC) has selected more robust suites
   such as TLS_ECDHE_RSA_WITH_AES_128_GCM_SHA256, which is also listed
   as a currently RECOMMENDED algorithm in [RFC8447bis] for their
   deployments of secure syslog.

   Additionally, RFC 8996 [BCP195] deprecates the use of DTLS 1.0
   [RFC4347], which is the mandatory-to-implement transport protocol per
   [RFC6012].  Therefore, that transport protocol must be updated.

   Finally, RFC 9325 [BCP195] provides guidance on the support of TLS
   1.3 [RFC8446] and DTLS 1.3 [RFC9147].

   Therefore, to maintain interoperability across implementations, the
   mandatory-to-implement cipher suites listed in [RFC5425] and
   [RFC6012] should be updated so that implementations of secure syslog
   will still interoperate and provide an acceptable and expected level
   of security.

   However, since there are many implementations of syslog using the
   cipher suites mandated by [RFC6012], a sudden change is not
   desirable.  To accommodate a migration path,
   TLS_RSA_WITH_AES_128_CBC_SHA or TLS_ECDHE_RSA_WITH_AES_128_GCM_SHA256
   may be used, but it is REQUIRED that
   TLS_ECDHE_RSA_WITH_AES_128_GCM_SHA256 be preferred.

4.  Updates to RFC 5425

   The mandatory-to-implement cipher suites are REQUIRED to be
   TLS_ECDHE_RSA_WITH_AES_128_GCM_SHA256 and
   TLS_RSA_WITH_AES_128_CBC_SHA.

   Implementations of [RFC5425] SHOULD offer
   TLS_ECDHE_RSA_WITH_AES_128_GCM_SHA256 but MAY offer
   TLS_RSA_WITH_AES_128_CBC_SHA.

   Implementations of [RFC5425] MUST continue to use TLS 1.2 [RFC5246]
   as the mandatory-to-implement transport protocol.

   As per RFC 9325 [BCP195], implementations of [RFC5425] SHOULD support
   TLS 1.3 [RFC8446] and, if implemented, MUST prefer to negotiate TLS
   1.3 over earlier versions of TLS.

5.  Updates to RFC 6012

   The mandatory-to-implement cipher suites are REQUIRED to be
   TLS_ECDHE_RSA_WITH_AES_128_GCM_SHA256 and
   TLS_RSA_WITH_AES_128_CBC_SHA.

   Implementations of [RFC6012] SHOULD offer
   TLS_ECDHE_RSA_WITH_AES_128_GCM_SHA256 but MAY offer
   TLS_RSA_WITH_AES_128_CBC_SHA.

   As specified in RFCs 8996 and 9325 [BCP195], implementations of
   [RFC6012] MUST NOT use DTLS 1.0 [RFC4347].  Implementations MUST use
   DTLS 1.2 [RFC6347].

   DTLS 1.2 [RFC6347] implementations SHOULD support and prefer the
   mandatory-to-implement cipher suite
   TLS_ECDHE_RSA_WITH_AES_128_GCM_SHA256.

   As per RFC 9325 [BCP195], implementations of [RFC6012] SHOULD support
   DTLS 1.3 [RFC9147] and, if implemented, MUST prefer to negotiate DTLS
   version 1.3 over earlier versions of DTLS.

6.  Early Data

   Early data (aka 0-RTT data) is a mechanism defined in TLS 1.3
   [RFC8446] that allows a client to send data ("early data") as part of
   the first flight of messages to a server.  Early data is permitted by
   TLS 1.3 when the client and server share a PSK, either obtained
   externally or via a previous handshake.  The client uses the PSK to
   authenticate the server and to encrypt the early data.

   As noted in Section 2.3 of [RFC8446bis], the security properties for
   early data are weaker than those for subsequent TLS-protected data.
   In particular, early data is not forward secret, and there are no
   protections against the replay of early data between connections.
   Appendix E.5 of [RFC8446bis] requires that applications not use early
   data without a profile that defines its use.  Because syslog does not
   support replay protection (see Section 8.4 of [RFC5424]) and most
   implementations establish a long-lived connection, this document
   specifies that implementations MUST NOT use early data.

7.  IANA Considerations

   This document has no IANA actions.

8.  Security Considerations

   RFCs 8996 and 9325 [BCP195] deprecate an insecure DTLS transport
   protocol from [RFC6012] and deprecate insecure cipher suites from
   [RFC5425] and [RFC6012].  However, the installed base of syslog
   implementations is not easily updated to immediately adhere to those
   changes.

   This document updates the mandatory-to-implement cipher suites to
   allow for a migration from TLS_RSA_WITH_AES_128_CBC_SHA to
   TLS_ECDHE_RSA_WITH_AES_128_GCM_SHA256 without deprecating the former.
   Implementations should prefer to use
   TLS_ECDHE_RSA_WITH_AES_128_GCM_SHA256.

   If a device currently only has TLS_RSA_WITH_AES_128_CBC_SHA, an
   administrator of the network should evaluate the conditions and
   determine if TLS_RSA_WITH_AES_128_CBC_SHA should be allowed so that
   syslog messages may continue to be delivered until the device is
   updated to have TLS_ECDHE_RSA_WITH_AES_128_GCM_SHA256.

9.  References

9.1.  Normative References

   [BCP195]   Best Current Practice 195,
              <https://www.rfc-editor.org/info/bcp195>.
              At the time of writing, this BCP comprises the following:

              Moriarty, K. and S. Farrell, "Deprecating TLS 1.0 and TLS
              1.1", BCP 195, RFC 8996, DOI 10.17487/RFC8996, March 2021,
              <https://www.rfc-editor.org/info/rfc8996>.

              Sheffer, Y., Saint-Andre, P., and T. Fossati,
              "Recommendations for Secure Use of Transport Layer
              Security (TLS) and Datagram Transport Layer Security
              (DTLS)", BCP 195, RFC 9325, DOI 10.17487/RFC9325, November
              2022, <https://www.rfc-editor.org/info/rfc9325>.

   [RFC2119]  Bradner, S., "Key words for use in RFCs to Indicate
              Requirement Levels", BCP 14, RFC 2119,
              DOI 10.17487/RFC2119, March 1997,
              <https://www.rfc-editor.org/info/rfc2119>.

   [RFC4347]  Rescorla, E. and N. Modadugu, "Datagram Transport Layer
              Security", RFC 4347, DOI 10.17487/RFC4347, April 2006,
              <https://www.rfc-editor.org/info/rfc4347>.

   [RFC5246]  Dierks, T. and E. Rescorla, "The Transport Layer Security
              (TLS) Protocol Version 1.2", RFC 5246,
              DOI 10.17487/RFC5246, August 2008,
              <https://www.rfc-editor.org/info/rfc5246>.

   [RFC5280]  Cooper, D., Santesson, S., Farrell, S., Boeyen, S.,
              Housley, R., and W. Polk, "Internet X.509 Public Key
              Infrastructure Certificate and Certificate Revocation List
              (CRL) Profile", RFC 5280, DOI 10.17487/RFC5280, May 2008,
              <https://www.rfc-editor.org/info/rfc5280>.

   [RFC5424]  Gerhards, R., "The Syslog Protocol", RFC 5424,
              DOI 10.17487/RFC5424, March 2009,
              <https://www.rfc-editor.org/info/rfc5424>.

   [RFC5425]  Miao, F., Ed., Ma, Y., Ed., and J. Salowey, Ed.,
              "Transport Layer Security (TLS) Transport Mapping for
              Syslog", RFC 5425, DOI 10.17487/RFC5425, March 2009,
              <https://www.rfc-editor.org/info/rfc5425>.

   [RFC6012]  Salowey, J., Petch, T., Gerhards, R., and H. Feng,
              "Datagram Transport Layer Security (DTLS) Transport
              Mapping for Syslog", RFC 6012, DOI 10.17487/RFC6012,
              October 2010, <https://www.rfc-editor.org/info/rfc6012>.

   [RFC6347]  Rescorla, E. and N. Modadugu, "Datagram Transport Layer
              Security Version 1.2", RFC 6347, DOI 10.17487/RFC6347,
              January 2012, <https://www.rfc-editor.org/info/rfc6347>.

   [RFC8174]  Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC
              2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174,
              May 2017, <https://www.rfc-editor.org/info/rfc8174>.

   [RFC8446]  Rescorla, E., "The Transport Layer Security (TLS) Protocol
              Version 1.3", RFC 8446, DOI 10.17487/RFC8446, August 2018,
              <https://www.rfc-editor.org/info/rfc8446>.

   [RFC9147]  Rescorla, E., Tschofenig, H., and N. Modadugu, "The
              Datagram Transport Layer Security (DTLS) Protocol Version
              1.3", RFC 9147, DOI 10.17487/RFC9147, April 2022,
              <https://www.rfc-editor.org/info/rfc9147>.

9.2.  Informative References

   [DEPRECATE-KEX]
              Bartle, C. and N. Aviram, "Deprecating Obsolete Key
              Exchange Methods in TLS 1.2", Work in Progress, Internet-
              Draft, draft-ietf-tls-deprecate-obsolete-kex-05, 3
              September 2024, <https://datatracker.ietf.org/doc/html/
              draft-ietf-tls-deprecate-obsolete-kex-05>.

   [RFC8446bis]
              Rescorla, E., "The Transport Layer Security (TLS) Protocol
              Version 1.3", Work in Progress, Internet-Draft, draft-
              ietf-tls-rfc8446bis-11, 14 September 2024,
              <https://datatracker.ietf.org/doc/html/draft-ietf-tls-
              rfc8446bis-11>.

   [RFC8447bis]
              Salowey, J. A. and S. Turner, "IANA Registry Updates for
              TLS and DTLS", Work in Progress, Internet-Draft, draft-
              ietf-tls-rfc8447bis-09, 30 April 2024,
              <https://datatracker.ietf.org/doc/html/draft-ietf-tls-
              rfc8447bis-09>.

Acknowledgments

   The authors would like to thank Arijit Kumar Bose, Steffen Fries, and
   the members of IEC TC57 WG15 for their review, comments, and
   suggestions.  The authors would also like to thank Tom Petch, Juergen
   Schoenwaelder, Hannes Tschofenig, Viktor Dukhovni, and the IESG
   members for their comments and constructive feedback.

Authors' Addresses

   Chris Lonvick
   Email: lonvick.ietf@gmail.com


   Sean Turner
   sn3rd
   Email: sean@sn3rd.com


   Joe Salowey
   Venafi
   Email: joe@salowey.net
