Secure Syslog Ciphers: Updates to the Cipher Suites in Secure Syslog
Secure syslog gets a forward-secret cipher suite and drops DTLS 1.0, without cutting off older devices.
Lonvick, C., Turner, S., and J. Salowey, "Updates to the Cipher Suites in Secure Syslog", RFC 9662, DOI 10.17487/RFC9662, October 2024, <https://www.rfc-editor.org/info/rfc9662>.
@misc{rfc9662,
series = {Request for Comments},
number = 9662,
howpublished = {RFC 9662},
publisher = {RFC Editor},
doi = {10.17487/RFC9662},
url = {https://www.rfc-editor.org/info/rfc9662},
author = {C. Lonvick and S. Turner and J. Salowey},
title = {{Updates to the Cipher Suites in Secure Syslog}},
pagetotal = 7,
year = 2024,
month = oct,
} RFC text
Contents
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
Provisions Relating to IETF Documents
(https://trustee.ietf.org/license-info) in effect on the date of
publication of this document. Please review these documents
carefully, as they describe your rights and restrictions with respect
to this document. Code Components extracted from this document must
include Revised BSD License text as described in Section 4.e of the
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
AI ELI5
On this page
§1Why Secure Syslog Needs an Update
RFC 5425 and RFC 6012 describe how to carry syslog messages securely over TLS and DTLS. Both require the cipher suite TLS_RSA_WITH_AES_128_CBC_SHA and both rely on RSA-based certificates and on versions of TLS and DTLS that are not the most recent.
RFC 5425 requires TLS 1.2. RFC 6012 requires DTLS 1.0. This document updates both RFCs to prefer TLS_ECDHE_RSA_WITH_AES_128_GCM_SHA256 over the old suite, and it also recommends a mandatory-to-implement secure datagram transport for RFC 6012.
Two older rule books for sending logs safely use locks that are now considered old. This new note says to use a better lock when you can.
§3The Case for Moving On
The RFC gives several reasons. TLS_RSA_WITH_AES_128_CBC_SHA does not provide forward secrecy, a feature the text calls highly desirable for securing event messages. It may also need mitigation techniques that can be hard to implement well. TLS_ECDHE_RSA_WITH_AES_128_GCM_SHA256 does provide forward secrecy.
Moving does not force operators to replace certificates. ECDHE cipher suites exist for both RSA and ECDSA certificates, so the RSA certificates already installed in devices can stay. Separately, DTLS 1.0 was deprecated by RFC 8996, so the transport that RFC 6012 made mandatory must change.
The text also notes that many syslog implementations use the suite mandated by RFC 6012, so a sudden change is not desirable. During the migration either suite may be used, but it is REQUIRED that TLS_ECDHE_RSA_WITH_AES_128_GCM_SHA256 be preferred.
The old lock can be picked in some tricky ways and does not protect yesterday's messages if someone steals the key later. The new lock fixes that, and your old keys still fit the door.
§4New Rules for Syslog over TLS
For RFC 5425, the mandatory-to-implement cipher suites are now REQUIRED to be TLS_ECDHE_RSA_WITH_AES_128_GCM_SHA256 and TLS_RSA_WITH_AES_128_CBC_SHA. Implementations SHOULD offer the ECDHE suite but MAY offer the older one.
TLS 1.2 stays the mandatory-to-implement transport protocol. Following RFC 9325, implementations SHOULD support TLS 1.3 and, if they implement it, MUST prefer to negotiate it over earlier versions.
Everyone must know how to use both locks. When you can, offer the new one first, and use the newest kind of lockbox if you have it.
| Topic | Syslog over TLS (RFC 5425) | Syslog over DTLS (RFC 6012) |
|---|---|---|
| Required suites | ECDHE_RSA_AES_128_GCM_SHA256 and RSA_AES_128_CBC_SHA | ECDHE_RSA_AES_128_GCM_SHA256 and RSA_AES_128_CBC_SHA |
| Offer | SHOULD offer the ECDHE suite | SHOULD offer the ECDHE suite |
| Mandatory version | TLS 1.2 | DTLS 1.2 (DTLS 1.0 MUST NOT be used) |
| Newest version | SHOULD support TLS 1.3 | SHOULD support DTLS 1.3 |
§5New Rules for Syslog over DTLS
For RFC 6012, the cipher suite rules are the same as for TLS: both suites are REQUIRED to be implemented, and implementations SHOULD offer the ECDHE suite but MAY offer the older one.
The transport rule changes more. Implementations MUST NOT use DTLS 1.0 (RFC 4347) and MUST use DTLS 1.2 (RFC 6347). DTLS 1.2 implementations SHOULD support and prefer TLS_ECDHE_RSA_WITH_AES_128_GCM_SHA256. Implementations SHOULD also support DTLS 1.3 (RFC 9147) and, if implemented, MUST prefer to negotiate it over earlier DTLS versions.
The old version of the secure postcard service is switched off. The next version is now the one everybody must be able to use, and an even newer one is welcome.
§6No Early Data
TLS 1.3 has a mechanism called early data (also called 0-RTT data) that lets a client send data in its first flight of messages, using a pre-shared key. The RFC points out that early data is not forward secret and has no protection against replay between connections.
Syslog does not support replay protection, and most implementations keep a long-lived connection anyway. So this document specifies that implementations MUST NOT use early data.
Sending a message before the secret handshake is finished is fast but risky, because a copycat could replay it. Since log connections stay open for a long time, nothing is lost by waiting, so it is not allowed.
§8Security and Migration
Earlier RFCs deprecated an insecure DTLS version and insecure cipher suites, but the installed base of syslog implementations cannot easily be updated at once. This document therefore lets TLS_RSA_WITH_AES_128_CBC_SHA stay as a required suite while directing implementations to prefer the ECDHE suite.
If a device currently only has the old suite, an administrator should evaluate the conditions and decide whether to keep allowing it, so syslog messages keep flowing until the device is updated. The RFC has no IANA actions.
If an old device cannot use the new lock yet, a grown-up decides whether it is safe enough to keep using the old one for a while.