TLS S. Farrell Internet-Draft Trinity College Dublin Intended status: Experimental 30 November 2024 Expires: 3 June 2025 PEM file format for ECH draft-farrell-tls-pemesni-08 Abstract Encrypted ClientHello (ECH) key pairs need to be configured into TLS servers, that can be built using different TLS libraries, so there is a benefit and little cost in documenting a file format to use for these key pairs, similar to how RFC7468 defines other PEM file formats. Status of This Memo This Internet-Draft is submitted in full conformance with the provisions of BCP 78 and BCP 79. Internet-Drafts are working documents of the Internet Engineering Task Force (IETF). Note that other groups may also distribute working documents as Internet-Drafts. The list of current Internet- Drafts is at https://datatracker.ietf.org/drafts/current/. Internet-Drafts are draft documents valid for a maximum of six months and may be updated, replaced, or obsoleted by other documents at any time. It is inappropriate to use Internet-Drafts as reference material or to cite them other than as "work in progress." This Internet-Draft will expire on 3 June 2025. 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. Farrell Expires 3 June 2025 [Page 1] Internet-Draft PEM file format for ECH November 2024 Table of Contents 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2 2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 2 3. ECHConfig file . . . . . . . . . . . . . . . . . . . . . . . 2 4. Security Considerations . . . . . . . . . . . . . . . . . . . 3 5. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 3 6. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 3 7. Normative References . . . . . . . . . . . . . . . . . . . . 3 Appendix A. Changes . . . . . . . . . . . . . . . . . . . . . . 4 Author's Address . . . . . . . . . . . . . . . . . . . . . . . . 5 1. Introduction Encrypted ClientHello (ECH) [I-D.ietf-tls-esni] for TLS1.3 [RFC8446] defines a confidentiality mechanism for server names and other ClientHello content in TLS. That requires publication of an ECHConfigList data structure in an HTTPS or SVCB RR [I-D.ietf-dnsop-svcb-https] in the DNS. An ECHConfigList can contain one or more ECHConfig values. An ECHConfig structure contains the public component of a key pair that will typically be periodically (re-)generated by some key manager for a TLS server. TLS servers then need to be configured to use these key pairs, and given that various TLS servers can be built with different TLS libraries, there is a benefit in having a standard format for ECH key pairs and configs, just as was done with [RFC7468]. [[At present, based on TLS WG list discussion, it seems most likely that this draft will be sent to the Independent stream once ECH is done and dusted (but not before). The source for this is in https://github.com/sftcd/pemesni/ PRs are welcome there too.]] 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. ECHConfig file A PEM ECH file contains zero or one private key and one encoded ECHConfigList. The public and private keys MUST both be PEM encoded. The file contains the concatenation of the PEM encoding of the private key (if present) followed by the PEM encoding of the public key as an Farrell Expires 3 June 2025 [Page 2] Internet-Draft PEM file format for ECH November 2024 ECHConfigList containing one ECHConfig that matches the private key. The private key MUST be encoded as a PKCS#8 PrivateKey. The public key MUST be the base64 encoded form of an ECHConfigList value that can also be published in the DNS. The string "ECHCONFIG" MUST be used in the PEM file delimiter for the public key. There MUST only be one key pair in each file even if a server publishes multiple public keys in the DNS in one ECHConfigList structure. Figure 1 shows an example ECHConfig PEM File -----BEGIN PRIVATE KEY----- MC4CAQAwBQYDK2VuBCIEICjd4yGRdsoP9gU7YT7My8DHx1Tjme8GYDXrOMCi8v1V -----END PRIVATE KEY----- -----BEGIN ECHCONFIG----- AD7+DQA65wAgACA8wVN2BtscOl3vQheUzHeIkVmKIiydUhDCliA4iyQRCwAEAAEA AQALZXhhbXBsZS5jb20AAA== -----END ECHCONFIG----- Figure 1: Example ECHConfig PEM file 4. Security Considerations Storing cryptographic keys in files leaves them vulnerable should anyone get read access to the filesystem on which they are stored. The same protection mechanims that would be used for a server's PEM encoded HTTPS certificate private key should be used for the PEM ECH configuration. 5. Acknowledgements Thanks to Daniel McCarney for comments. 6. IANA Considerations There are none so this section can be deleted later. 7. Normative References [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate Requirement Levels", BCP 14, RFC 2119, DOI 10.17487/RFC2119, March 1997, . [RFC7468] Josefsson, S. and S. Leonard, "Textual Encodings of PKIX, PKCS, and CMS Structures", RFC 7468, DOI 10.17487/RFC7468, April 2015, . Farrell Expires 3 June 2025 [Page 3] Internet-Draft PEM file format for ECH November 2024 [RFC8174] Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC 2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174, May 2017, . [RFC8446] Rescorla, E., "The Transport Layer Security (TLS) Protocol Version 1.3", RFC 8446, DOI 10.17487/RFC8446, August 2018, . [I-D.ietf-tls-esni] Rescorla, E., Oku, K., Sullivan, N., and C. A. Wood, "TLS Encrypted Client Hello", Work in Progress, Internet-Draft, draft-ietf-tls-esni-22, 15 September 2024, . [I-D.ietf-dnsop-svcb-https] Schwartz, B. M., Bishop, M., and E. Nygren, "Service binding and parameter specification via the DNS (DNS SVCB and HTTPS RRs)", Work in Progress, Internet-Draft, draft- ietf-dnsop-svcb-https-12, 11 March 2023, . Appendix A. Changes From -07 to -08: * Processed some github comments From -06 to -07: * Refresh due to expiry. From -05 to -06: * Refresh due to expiry. From -04 to -05: * Refresh due to expiry. From -03 to -04: * Refresh due to expiry. From -02 to -03: * Refresh due to expiry and not possible ISE destination Farrell Expires 3 June 2025 [Page 4] Internet-Draft PEM file format for ECH November 2024 From -01 to -02: * ECHO -> ECH From -00 to -01: * ESNI -> ECHO Author's Address Stephen Farrell Trinity College Dublin Dublin 2 Ireland Phone: +353-1-896-2354 Email: stephen.farrell@cs.tcd.ie Farrell Expires 3 June 2025 [Page 5]