TLS                                                           S. Farrell
Internet-Draft                                    Trinity College Dublin
Intended status: Experimental                           19 November 2021
Expires: 23 May 2022


                        PEM file format for ECH
                      draft-farrell-tls-pemesni-02

Abstract

   Encrypted ClientHello (ECH) key pairs need to be configured into TLS
   servers, some of which can be built with different TLS libraries, so
   there is a benefit and little cost in documenting a file format to
   use for these, similar to how RFC7468 defines other PEM file formats.

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   This Internet-Draft will expire on 23 May 2022.

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Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   2
   2.  Terminology . . . . . . . . . . . . . . . . . . . . . . . . .   2
   3.  ECHConfig file  . . . . . . . . . . . . . . . . . . . . . . .   3
   4.  Security Considerations . . . . . . . . . . . . . . . . . . .   3
   5.  Acknowledgements  . . . . . . . . . . . . . . . . . . . . . .   3
   6.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .   3
   7.  Normative References  . . . . . . . . . . . . . . . . . . . .   3
   Appendix A.  Changes  . . . . . . . . . . . . . . . . . . . . . .   4
   Author's Address  . . . . . . . . . . . . . . . . . . . . . . . .   4

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, just as
   was done with [RFC7468].

   [[This idea could: a) wither on the vine, b) be published as it's own
   RFC, or c) end up as a PR for [I-D.ietf-tls-esni].  There is no
   absolute need for this to be in the RFC that defines ECHO, so (b)
   seems feasible if there's enough interest, hence this draft.  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.










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3.  ECHConfig file

   The public and private keys MUST both be PEM encoded.  The file
   contains the catenation of the PEM encoding of the private key
   followed by the PEM encoding of the public key as an ECHConfigList
   containing exactly one ECHConfig.  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 shell access to the TLS server machine.  So: Don't let
   that happen:-)

5.  Acknowledgements

   TBD, as needed

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>.




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   [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>.

   [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-13, 12 August 2021,
              <https://www.ietf.org/archive/id/draft-ietf-tls-esni-
              13.txt>.

   [I-D.ietf-dnsop-svcb-https]
              Schwartz, B., 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-08, 12 October 2021,
              <https://www.ietf.org/archive/id/draft-ietf-dnsop-svcb-
              https-08.txt>.

Appendix A.  Changes

   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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