Updates to the Cipher Suites in Secure Syslog

Status of This Memo

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Table of Contents

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

[I-D.salowey-tls-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] REQUIRE 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. [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.¶

[I-D.saviram-tls-deprecate-obsolete-kex] documents that the cipher suite TLS_RSA_WITH_AES_128_CBC_SHA has been found to be weak. As such, the community is moving away from that and other weak suites and towards more robust suites such as TLS_ECDHE_RSA_WITH_AES_128_GCM_SHA256, which is also listed as a currently Recommended algorithm in [I-D.salowey-tls-rfc8447bis].¶

Along those lines, [I-D.ietf-uta-rfc7525bis] 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.¶

Therefore, the mandatory to implement cipher suites listed in [RFC5425] and [RFC6012] must be updated so that implementations of secure syslog are still considered to provide an acceptable and expected level of security.¶

Additionally, [BCP195] [RFC8996] deprecates the use of DTLS 1.0 [RFC4347], which is the mandatory to implement transport protocol for [RFC6012]. Therefore, the transport protocol for [RFC6012] must be updated.¶

4. Updates to RFC 5425

Implementations of [RFC5425] MUST NOT offer TLS_RSA_WITH_AES_128_CBC_SHA. The mandatory to implement cipher suite is REQUIRED to be TLS_ECDHE_RSA_WITH_AES_128_GCM_SHA256.¶

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

Implementations of [RFC5425] MAY use TLS 1.3 [RFC8446] as a transport as long as they support the currently recommended cipher suites.¶

5. Updates to RFC 6012

Implementations of [RFC6012] MUST NOT offer TLS_RSA_WITH_AES_128_CBC_SHA. The mandatory to implement cipher suite is REQUIRED to be TLS_ECDHE_RSA_WITH_AES_128_GCM_SHA256.¶

As specified in [BCP195], implementations of [RFC6012] must not use DTLS 1.0 [RFC4347]. Implementations MUST use DTLS 1.2 [RFC6347].¶

DTLS 1.2 [RFC6347] implementations are REQUIRED to support the mandatory to implement cipher suite, which is TLS_ECDHE_RSA_WITH_AES_128_GCM_SHA256.¶

Implementations of [RFC6012] MAY use DTLS 1.3 [I-D.ietf-tls-dtls13] as a transport as long as they support the currently recommended cipher suites.¶

EDITOR's NOTE: Need to address 0-RTT considerations.¶

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 [I-D.ietf-tls-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 [I-D.ietf-tls-rfc8446bis] requires 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. Authors Notes

This section will be removed prior to publication.¶

This is version -01 for the UTA Working Group. This version proposes a section to address early data (aka 0-RTT data).¶

Members of IEC 62351 TC 57 WG15, who prompted this work, have proposed the following text to be inserted into their documents.¶

The selection of TLS connection parameters such as cipher suites, session resumption and renegotiation shall be reused from IEC 62351-3 specification. Note that port TCP/6514 is assigned by IANA to RFC 5425 (syslog-tls). The RFC requires the support of TLS1.2 and a SHA-1 based cipher suite, but does not mandate its use. The cipher does not align with IEC 62351-3 Ed.2 for profiling TLS. Nevertheless, RFC 5425 does not rule out to use stronger cipher suites. With this, clients and server supporting the selection of cipher suites stated in IEC 62351-3 Ed2 will not experience interoperability problems. Caution has to be taken in environments in which interworking with existing services utilizing syslog over TLS is intended. For these, the syslog server needs to be enabled to support the required cipher suites. This ensures connectivity with clients complying to this document and others complying to RFC 5425. Note that meanwhile the work on an update of RFC 5425 and RFC 6012 has started. It targets the adoption of stronger cipher suites for TLS and DTLS to protect syslog communication.¶

Comments on this text are welcome.¶

8. 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 and Juergen Schoenwaelder for their comments and constructive feedback.¶

9. IANA Considerations

This document makes no requests to IANA.¶

10. Security Considerations

[BCP195] deprecates an insecure DTLS transport protocol from [RFC6012] and deprecates insecure cipher suits from [RFC5425] and [RFC6012]. This document specifies mandatory to implement cipher suites to those RFCs and the latest version of the DTLS protocol to [RFC6012].¶

Authors' Addresses