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PEM file format for ECH
draft-farrell-tls-pemesni-08

Document Type Active Internet-Draft (individual)
Author Stephen Farrell
Last updated 2024-11-30
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draft-farrell-tls-pemesni-08
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.

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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.  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

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   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,
              <https://www.rfc-editor.org/info/rfc2119>.

   [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>.

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   [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-22, 15 September 2024,
              <https://datatracker.ietf.org/doc/html/draft-ietf-tls-
              esni-22>.

   [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,
              <https://datatracker.ietf.org/doc/html/draft-ietf-dnsop-
              svcb-https-12>.

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

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   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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