lonvick.ietf@gmail.com

sn3rd

sean@sn3rd.com

Venafi

joe@salowey.net

SEC uts syslog secure syslog TLS_RSA_WITH_AES_128_CBC_SHA TLS_ECDHE_RSA_WITH_AES_128_GCM_SHA256 DTLS TLS cipher suite 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 .

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 () 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

• .  Introduction
• .  Terminology
• .  Support for Updating
• .  Updates to RFC 5425
• .  Updates to RFC 6012
• .  Early Data
• .  IANA Considerations
• .  Security Considerations
• .  References
  • .  Normative References
  • .  Informative References
• Acknowledgments
• Authors' Addresses

Introduction "Transport Layer Security (TLS) Transport Mapping for Syslog" and "Datagram Transport Layer Security (DTLS) Transport Mapping for Syslog" 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. requires that implementations MUST support TLS 1.2 and are REQUIRED to support the mandatory-to-implement cipher suite TLS_RSA_WITH_AES_128_CBC_SHA. requires that implementations "MUST" support DTLS 1.0 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 has been deprecated by RFC 8996 , and the community is moving to DTLS 1.2 and DTLS 1.3 . This document updates and 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 by recommending a mandatory-to-implement secure datagram transport.

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 when, and only when, they appear in all capitals, as shown here.

Support for Updating 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 . Since both and 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 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. 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 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 for their deployments of secure syslog. Additionally, RFC 8996 deprecates the use of DTLS 1.0 , which is the mandatory-to-implement transport protocol per . Therefore, that transport protocol must be updated. Finally, RFC 9325 provides guidance on the support of TLS 1.3 and DTLS 1.3 . Therefore, to maintain interoperability across implementations, the mandatory-to-implement cipher suites listed in and 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 , 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.

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 SHOULD offer TLS_ECDHE_RSA_WITH_AES_128_GCM_SHA256 but MAY offer TLS_RSA_WITH_AES_128_CBC_SHA. Implementations of MUST continue to use TLS 1.2 as the mandatory-to-implement transport protocol. As per RFC 9325 , implementations of SHOULD support TLS 1.3 and, if implemented, MUST prefer to negotiate TLS 1.3 over earlier versions of TLS.

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 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 , implementations of MUST NOT use DTLS 1.0 . Implementations MUST use DTLS 1.2 . DTLS 1.2 implementations SHOULD support and prefer the mandatory-to-implement cipher suite TLS_ECDHE_RSA_WITH_AES_128_GCM_SHA256. As per RFC 9325 , implementations of SHOULD support DTLS 1.3 and, if implemented, MUST prefer to negotiate DTLS version 1.3 over earlier versions of DTLS.

Early Data Early data (aka 0-RTT data) is a mechanism defined in TLS 1.3 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 , 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. requires that applications not use early data without a profile that defines its use. Because syslog does not support replay protection (see ) and most implementations establish a long-lived connection, this document specifies that implementations MUST NOT use early data.

IANA Considerations This document has no IANA actions.

Security Considerations RFCs 8996 and 9325 deprecate an insecure DTLS transport protocol from and deprecate insecure cipher suites from and . 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.

References Normative References This document formally deprecates Transport Layer Security (TLS) versions 1.0 (RFC 2246) and 1.1 (RFC 4346). Accordingly, those documents have been moved to Historic status. These versions lack support for current and recommended cryptographic algorithms and mechanisms, and various government and industry profiles of applications using TLS now mandate avoiding these old TLS versions. TLS version 1.2 became the recommended version for IETF protocols in 2008 (subsequently being obsoleted by TLS version 1.3 in 2018), providing sufficient time to transition away from older versions. Removing support for older versions from implementations reduces the attack surface, reduces opportunity for misconfiguration, and streamlines library and product maintenance. This document also deprecates Datagram TLS (DTLS) version 1.0 (RFC 4347) but not DTLS version 1.2, and there is no DTLS version 1.1. This document updates many RFCs that normatively refer to TLS version 1.0 or TLS version 1.1, as described herein. This document also updates the best practices for TLS usage in RFC 7525; hence, it is part of BCP 195. Transport Layer Security (TLS) and Datagram Transport Layer Security (DTLS) are used to protect data exchanged over a wide range of application protocols and can also form the basis for secure transport protocols. Over the years, the industry has witnessed several serious attacks on TLS and DTLS, including attacks on the most commonly used cipher suites and their modes of operation. This document provides the latest recommendations for ensuring the security of deployed services that use TLS and DTLS. These recommendations are applicable to the majority of use cases. RFC 7525, an earlier version of the TLS recommendations, was published when the industry was transitioning to TLS 1.2. Years later, this transition is largely complete, and TLS 1.3 is widely available. This document updates the guidance given the new environment and obsoletes RFC 7525. In addition, this document updates RFCs 5288 and 6066 in view of recent attacks. In many standards track documents several words are used to signify the requirements in the specification. These words are often capitalized. This document defines these words as they should be interpreted in IETF documents. This document specifies an Internet Best Current Practices for the Internet Community, and requests discussion and suggestions for improvements. This document specifies Version 1.0 of the Datagram Transport Layer Security (DTLS) protocol. The DTLS protocol provides communications privacy for datagram protocols. The protocol allows client/server applications to communicate in a way that is designed to prevent eavesdropping, tampering, or message forgery. The DTLS protocol is based on the Transport Layer Security (TLS) protocol and provides equivalent security guarantees. Datagram semantics of the underlying transport are preserved by the DTLS protocol. This document specifies Version 1.2 of the Transport Layer Security (TLS) protocol. The TLS protocol provides communications security over the Internet. The protocol allows client/server applications to communicate in a way that is designed to prevent eavesdropping, tampering, or message forgery. [STANDARDS-TRACK] This memo profiles the X.509 v3 certificate and X.509 v2 certificate revocation list (CRL) for use in the Internet. An overview of this approach and model is provided as an introduction. The X.509 v3 certificate format is described in detail, with additional information regarding the format and semantics of Internet name forms. Standard certificate extensions are described and two Internet-specific extensions are defined. A set of required certificate extensions is specified. The X.509 v2 CRL format is described in detail along with standard and Internet-specific extensions. An algorithm for X.509 certification path validation is described. An ASN.1 module and examples are provided in the appendices. [STANDARDS-TRACK] This document describes the syslog protocol, which is used to convey event notification messages. This protocol utilizes a layered architecture, which allows the use of any number of transport protocols for transmission of syslog messages. It also provides a message format that allows vendor-specific extensions to be provided in a structured way. This document has been written with the original design goals for traditional syslog in mind. The need for a new layered specification has arisen because standardization efforts for reliable and secure syslog extensions suffer from the lack of a Standards-Track and transport-independent RFC. Without this document, each other standard needs to define its own syslog packet format and transport mechanism, which over time will introduce subtle compatibility issues. This document tries to provide a foundation that syslog extensions can build on. This layered architecture approach also provides a solid basis that allows code to be written once for each syslog feature rather than once for each transport. [STANDARDS-TRACK] This document describes the use of Transport Layer Security (TLS) to provide a secure connection for the transport of syslog messages. This document describes the security threats to syslog and how TLS can be used to counter such threats. [STANDARDS-TRACK] This document describes the transport of syslog messages over the Datagram Transport Layer Security (DTLS) protocol. It provides a secure transport for syslog messages in cases where a connectionless transport is desired. [STANDARDS-TRACK] This document specifies version 1.2 of the Datagram Transport Layer Security (DTLS) protocol. The DTLS protocol provides communications privacy for datagram protocols. The protocol allows client/server applications to communicate in a way that is designed to prevent eavesdropping, tampering, or message forgery. The DTLS protocol is based on the Transport Layer Security (TLS) protocol and provides equivalent security guarantees. Datagram semantics of the underlying transport are preserved by the DTLS protocol. This document updates DTLS 1.0 to work with TLS version 1.2. [STANDARDS-TRACK] RFC 2119 specifies common key words that may be used in protocol specifications. This document aims to reduce the ambiguity by clarifying that only UPPERCASE usage of the key words have the defined special meanings. This document specifies version 1.3 of the Transport Layer Security (TLS) protocol. TLS allows client/server applications to communicate over the Internet in a way that is designed to prevent eavesdropping, tampering, and message forgery. This document updates RFCs 5705 and 6066, and obsoletes RFCs 5077, 5246, and 6961. This document also specifies new requirements for TLS 1.2 implementations. This document specifies version 1.3 of the Datagram Transport Layer Security (DTLS) protocol. DTLS 1.3 allows client/server applications to communicate over the Internet in a way that is designed to prevent eavesdropping, tampering, and message forgery. The DTLS 1.3 protocol is based on the Transport Layer Security (TLS) 1.3 protocol and provides equivalent security guarantees with the exception of order protection / non-replayability. Datagram semantics of the underlying transport are preserved by the DTLS protocol. This document obsoletes RFC 6347. Informative References Roblox This document deprecates the use of RSA key exchange and Diffie Hellman over a finite field in TLS 1.2, and discourages the use of static elliptic curve Diffie Hellman cipher suites. Note that these prescriptions apply only to TLS 1.2 since TLS 1.0 and 1.1 are deprecated by RFC 8996 and TLS 1.3 either does not use the affected algorithm or does not share the relevant configuration options. This document updates RFCs 9325, 4346, 5246, 4162, 6347, 5932, 5288, 6209, 6367, 8422, 5289, 5469, 4785, 4279, 5487, 6655, and 7905. Work in Progress Independent This document specifies version 1.3 of the Transport Layer Security (TLS) protocol. TLS allows client/server applications to communicate over the Internet in a way that is designed to prevent eavesdropping, tampering, and message forgery. This document updates RFCs 5705, 6066, 7627, and 8422 and obsoletes RFCs 5077, 5246, 6961, 8422, and 8446. This document also specifies new requirements for TLS 1.2 implementations. Work in Progress Venafi sn3rd This document updates the changes to TLS and DTLS IANA registries made in RFC 8447. It adds a new value "D" for discouraged to the recommended column of the selected TLS registries. This document updates the following RFCs: 3749, 5077, 4680, 5246, 5705, 5878, 6520, 7301, and 8447. Work in Progress

Acknowledgments The authors would like to thank , , and the members of IEC TC57 WG15 for their review, comments, and suggestions. The authors would also like to thank , , , , and the IESG members for their comments and constructive feedback.

Authors' Addresses

lonvick.ietf@gmail.com

sn3rd

sean@sn3rd.com

Venafi

joe@salowey.net