PEM file format for ECH
draft-farrell-tls-pemesni-11

Internet Engineering Task Force (IETF) S. Farrell
Internet-Draft Trinity College Dublin
Intended status: Standards Track 4 December 2025
Expires: 7 June 2026
 PEM file format for ECH
 draft-farrell-tls-pemesni-11
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
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 provisions of BCP 78 and BCP 79.
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 Task Force (IETF). Note that other groups may also distribute
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 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 7 June 2026.
Copyright Notice
 Copyright (c) 2025 IETF Trust and the persons identified as the
 document authors. All rights reserved.
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 Provisions Relating to IETF Documents (https://trustee.ietf.org/
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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. References . . . . . . . . . . . . . . . . . . . . . . . . . 3
 7.1. Normative References . . . . . . . . . . . . . . . . . . 3
 7.2. Informative References . . . . . . . . . . . . . . . . . 4
 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 [RFC9460] 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].
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.
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 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
 ECHConfigList containing an 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.
 Any content after the PEM encoded ECHConfigList SHOULD be ignored.
 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
 This document contains no IANA considerations.
7. References
7.1. Normative References
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 [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>.
 [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>.
 [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-25, 14 June 2025,
 <https://datatracker.ietf.org/doc/html/draft-ietf-tls-
 esni-25>.
7.2. Informative References
 [RFC7468] Josefsson, S. and S. Leonard, "Textual Encodings of PKIX,
 PKCS, and CMS Structures", RFC 7468, DOI 10.17487/RFC7468,
 April 2015, <https://www.rfc-editor.org/info/rfc7468>.
 [RFC9460] Schwartz, B., Bishop, M., and E. Nygren, "Service Binding
 and Parameter Specification via the DNS (SVCB and HTTPS
 Resource Records)", RFC 9460, DOI 10.17487/RFC9460,
 November 2023, <https://www.rfc-editor.org/info/rfc9460>.
Appendix A. Changes
 From -10 to -11:
 * Change to standards track as agreed with shepherd/AD.
 From -09 to -10:
 * Tweaks to fit being AD sponsored.
 From -08 to -09:
 * Minor clarificatrion of encoding based on current OpenSSL ECH
 feature branch code.
 From -07 to -08:
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 * 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
 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
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