rfc9934.original   rfc9934.txt 
Internet Engineering Task Force (IETF) S. Farrell Internet Engineering Task Force (IETF) S. Farrell
Internet-Draft Trinity College Dublin Request for Comments: 9934 Trinity College Dublin
Intended status: Standards Track 23 January 2026 Category: Standards Track February 2026
Expires: 27 July 2026 ISSN: 2070-1721
PEM file format for ECH Privacy-Enhanced Mail (PEM) File Format for Encrypted ClientHello (ECH)
draft-farrell-tls-pemesni-13
Abstract Abstract
Encrypted ClientHello (ECH) key pairs need to be configured into TLS Encrypted ClientHello (ECH) key pairs need to be configured into TLS
servers, which can be built using different TLS libraries. This servers, which can be built using different TLS libraries. This
document specifies a file format to use, similar to how RFC 7468 document specifies a standard file format for this purpose, similar
defines other PEM file formats. to how RFC 7468 defines other Privacy-Enhanced Mail (PEM) file
formats.
Status of This Memo Status of This Memo
This Internet-Draft is submitted in full conformance with the This is an Internet Standards Track document.
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 This document is a product of the Internet Engineering Task Force
and may be updated, replaced, or obsoleted by other documents at any (IETF). It represents the consensus of the IETF community. It has
time. It is inappropriate to use Internet-Drafts as reference received public review and has been approved for publication by the
material or to cite them other than as "work in progress." Internet Engineering Steering Group (IESG). Further information on
Internet Standards is available in Section 2 of RFC 7841.
This Internet-Draft will expire on 27 July 2026. Information about the current status of this document, any errata,
and how to provide feedback on it may be obtained at
https://www.rfc-editor.org/info/rfc9934.
Copyright Notice Copyright Notice
Copyright (c) 2026 IETF Trust and the persons identified as the Copyright (c) 2026 IETF Trust and the persons identified as the
document authors. All rights reserved. document authors. All rights reserved.
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Table of Contents Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2 1. Introduction
2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 2 2. Terminology
3. ECHConfig file . . . . . . . . . . . . . . . . . . . . . . . 2 3. ECHConfig File
4. Security Considerations . . . . . . . . . . . . . . . . . . . 4 4. Security Considerations
5. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 4 5. IANA Considerations
6. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 4 6. References
7. References . . . . . . . . . . . . . . . . . . . . . . . . . 4 6.1. Normative References
7.1. Normative References . . . . . . . . . . . . . . . . . . 4 6.2. Informative References
7.2. Informative References . . . . . . . . . . . . . . . . . 5 Acknowledgements
Appendix A. Changes . . . . . . . . . . . . . . . . . . . . . . 5 Author's Address
Author's Address . . . . . . . . . . . . . . . . . . . . . . . . 6
1. Introduction 1. Introduction
Encrypted ClientHello (ECH) [I-D.ietf-tls-esni] for TLS1.3 [RFC8446] Encrypted ClientHello (ECH) [RFC9849] for TLS1.3 [RFC8446] defines a
defines a confidentiality mechanism for server names and other confidentiality mechanism for server names and other ClientHello
ClientHello content in TLS. That requires publication of an content in TLS. That requires publication of an ECHConfigList data
ECHConfigList data structure in an HTTPS or SVCB RR [RFC9460] in the structure in an HTTPS or SVCB RR [RFC9460] in the DNS. An
DNS. An ECHConfigList can contain one or more ECHConfig values. An ECHConfigList can contain one or more ECHConfig values. An ECHConfig
ECHConfig structure contains the public component of a key pair that structure contains the public component of a key pair that will
will typically be periodically (re-)generated by some key manager for typically be periodically (re-)generated by some key manager for a
a TLS server. TLS servers then need to be configured to use these TLS server. TLS servers then need to be configured to use these key
key pairs, and given that various TLS servers can be built with pairs, and given that various TLS servers can be built with different
different TLS libraries, there is a benefit in having a standard TLS libraries, there is a benefit in having a standard format for ECH
format for ECH key pairs and configs, just as was done with key pairs and configs, just as was done with [RFC7468].
[RFC7468].
2. Terminology 2. Terminology
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and "SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and
"OPTIONAL" in this document are to be interpreted as described in BCP "OPTIONAL" in this document are to be interpreted as described in
14 [RFC2119] [RFC8174] when, and only when, they appear in all BCP 14 [RFC2119] [RFC8174] when, and only when, they appear in all
capitals, as shown here. capitals, as shown here.
3. ECHConfig file 3. ECHConfig File
A PEM ECH file contains zero or one private key and one encoded A PEM ECH file contains zero or one private key and one encoded
ECHConfigList. ECHConfigList.
The public and private keys MUST both be PEM encoded [RFC7468]. The The public and private keys MUST both be PEM encoded [RFC7468]. The
file contains the concatenation of the PEM encoding of the private file contains the concatenation of the PEM encoding of the private
key (if present) followed by the PEM encoding of the public key(s) as key (if present) followed by the PEM encoding of the public key(s) as
an ECHConfigList. When a private key is present, the ECHConfigList an ECHConfigList. When a private key is present, the ECHConfigList
MUST contain an ECHConfig that matches the private key. The private MUST contain an ECHConfig that matches the private key. The private
key MUST be encoded as a PKCS#8 PrivateKey [RFC7468]. The public key MUST be encoded as a PKCS#8 PrivateKey [RFC7468]. The public
key(s) MUST be the base64 encoded (see Section 4 of [RFC4648]) form key(s) MUST be the base64-encoded form (see Section 4 of [RFC4648])
of an ECHConfigList value that can be published in the DNS using an of an ECHConfigList value that can be published in the DNS using an
HTTPS RR as described in [I-D.ietf-tls-svcb-ech]. The string HTTPS RR as described in [RFC9848]. The string "ECHCONFIG" MUST be
"ECHCONFIG" MUST be used in the PEM file delimiter for the public used in the PEM file delimiter for the public key.
key.
Any content after the PEM encoded ECHConfigList SHOULD be ignored. Any content after the PEM encoded ECHConfigList SHOULD be ignored.
Figure 1 shows an example ECHConfig PEM File Figure 1 shows an example ECHConfig PEM File
-----BEGIN PRIVATE KEY----- -----BEGIN PRIVATE KEY-----
MC4CAQAwBQYDK2VuBCIEICjd4yGRdsoP9gU7YT7My8DHx1Tjme8GYDXrOMCi8v1V MC4CAQAwBQYDK2VuBCIEICjd4yGRdsoP9gU7YT7My8DHx1Tjme8GYDXrOMCi8v1V
-----END PRIVATE KEY----- -----END PRIVATE KEY-----
-----BEGIN ECHCONFIG----- -----BEGIN ECHCONFIG-----
AD7+DQA65wAgACA8wVN2BtscOl3vQheUzHeIkVmKIiydUhDCliA4iyQRCwAEAAEA AD7+DQA65wAgACA8wVN2BtscOl3vQheUzHeIkVmKIiydUhDCliA4iyQRCwAEAAEA
AQALZXhhbXBsZS5jb20AAA== AQALZXhhbXBsZS5jb20AAA==
-----END ECHCONFIG----- -----END ECHCONFIG-----
Figure 1: Example ECHConfig PEM file Figure 1: Example ECHConfig PEM File
If the above ECHConfigList were published in the DNS for If the above ECHConfigList were published in the DNS for
foo.example.com, then one could access that as shown in Figure 2. foo.example.com, then one could access that as shown in Figure 2.
$ dig +short HTTPS foo.example.com $ dig +short HTTPS foo.example.com
1 . ech=AD7+DQA65wAgACA8wVN2BtscOl3vQheUzHeIkVmKIiydUhDCliA4iyQR 1 . ech=AD7+DQA65wAgACA8wVN2BtscOl3vQheUzHeIkVmKIiydUhDCliA4iyQR
wAEAAEAAQALZXhhbXBsZS5jb20AAA== wAEAAEAAQALZXhhbXBsZS5jb20AAA==
Figure 2: Use of dig to get the ECHConfigList from DNS Figure 2: Use of Dig to Get the ECHConfigList from DNS
TLS servers using this file format might configure multiple file TLS servers using this file format might configure multiple file
names as part of their overall configuration, if, for example, only names as part of their overall configuration, if, for example, only
the ECHConfigList values from a subset of those files are to be used the ECHConfigList values from a subset of those files are to be used
as the value for retry_configs in the ECH fallback scenario. as the value for retry_configs in the ECH fallback scenario.
The ECHConfigList in a PEM file might contain more than one ECHConfig The ECHConfigList in a PEM file might contain more than one ECHConfig
if, for example, those ECHConfig values contain different extensions if, for example, those ECHConfig values contain different extensions
or different public_name values. Consistent with or different public_name values. Consistent with [RFC9849], the
[I-D.ietf-tls-esni], the ECHConfig values within an ECHConfigList ECHConfig values within an ECHConfigList appear in decreasing order
appear in decreasing order of preference. If the ECHConfigList value of preference. If the ECHConfigList value is to be used as the
is to be used as the retry_configs value, then that might contain retry_configs value, then that might contain different public keys.
different public keys. (Nonetheless, when a private key is present, (Nonetheless, when a private key is present, that MUST match the
that MUST match the public key from one of the ECHConfig values.) public key from one of the ECHConfig values.)
4. Security Considerations 4. Security Considerations
Storing cryptographic keys in files leaves them vulnerable should Storing cryptographic keys in files leaves them vulnerable should
anyone get read access to the filesystem on which they are stored. anyone get read access to the filesystem on which they are stored.
The same protection mechanisms that would be used for a server's PEM The same protection mechanisms that would be used for a server's PEM-
encoded HTTPS certificate private key should be used for the PEM ECH encoded HTTPS certificate private key should be used for the PEM ECH
configuration. configuration.
The security considerations of [I-D.ietf-tls-svcb-ech] apply when The security considerations of [RFC9848] apply when retrieving an
retrieving an ECHConfigList from the DNS. ECHConfigList from the DNS.
For clarity, only the ECHConfigList is to be published in the DNS - For clarity, only the ECHConfigList is to be published in the DNS -
the private key from an ECH PEM file MUST NOT be published in the the private key from an ECH PEM file MUST NOT be published in the
DNS. DNS.
5. Acknowledgements 5. IANA Considerations
Thanks to Daniel McCarney, Jim Reid and Peter Yee for comments.
6. IANA Considerations
This document contains no IANA considerations. This document has no IANA actions.
7. References 6. References
7.1. Normative References 6.1. Normative References
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, Requirement Levels", BCP 14, RFC 2119,
DOI 10.17487/RFC2119, March 1997, DOI 10.17487/RFC2119, March 1997,
<https://www.rfc-editor.org/info/rfc2119>. <https://www.rfc-editor.org/info/rfc2119>.
[RFC4648] Josefsson, S., "The Base16, Base32, and Base64 Data [RFC4648] Josefsson, S., "The Base16, Base32, and Base64 Data
Encodings", RFC 4648, DOI 10.17487/RFC4648, October 2006, Encodings", RFC 4648, DOI 10.17487/RFC4648, October 2006,
<https://www.rfc-editor.org/info/rfc4648>. <https://www.rfc-editor.org/info/rfc4648>.
skipping to change at page 5, line 5 skipping to change at line 178
April 2015, <https://www.rfc-editor.org/info/rfc7468>. April 2015, <https://www.rfc-editor.org/info/rfc7468>.
[RFC8174] Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC [RFC8174] Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC
2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174, 2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174,
May 2017, <https://www.rfc-editor.org/info/rfc8174>. May 2017, <https://www.rfc-editor.org/info/rfc8174>.
[RFC8446] Rescorla, E., "The Transport Layer Security (TLS) Protocol [RFC8446] Rescorla, E., "The Transport Layer Security (TLS) Protocol
Version 1.3", RFC 8446, DOI 10.17487/RFC8446, August 2018, Version 1.3", RFC 8446, DOI 10.17487/RFC8446, August 2018,
<https://www.rfc-editor.org/info/rfc8446>. <https://www.rfc-editor.org/info/rfc8446>.
[I-D.ietf-tls-esni] [RFC9849] Rescorla, E., Oku, K., Sullivan, N., and C. A. Wood, "TLS
Rescorla, E., Oku, K., Sullivan, N., and C. A. Wood, "TLS Encrypted Client Hello", RFC 9849, DOI 10.17487/RFC9849,
Encrypted Client Hello", Work in Progress, Internet-Draft, February 2026, <https://www.rfc-editor.org/info/rfc9849>.
draft-ietf-tls-esni-25, 14 June 2025,
<https://datatracker.ietf.org/doc/html/draft-ietf-tls-
esni-25>.
7.2. Informative References 6.2. Informative References
[RFC9460] Schwartz, B., Bishop, M., and E. Nygren, "Service Binding [RFC9460] Schwartz, B., Bishop, M., and E. Nygren, "Service Binding
and Parameter Specification via the DNS (SVCB and HTTPS and Parameter Specification via the DNS (SVCB and HTTPS
Resource Records)", RFC 9460, DOI 10.17487/RFC9460, Resource Records)", RFC 9460, DOI 10.17487/RFC9460,
November 2023, <https://www.rfc-editor.org/info/rfc9460>. November 2023, <https://www.rfc-editor.org/info/rfc9460>.
[I-D.ietf-tls-svcb-ech] [RFC9848] Schwartz, B. M., Bishop, M., and E. Nygren, "Bootstrapping
Schwartz, B. M., Bishop, M., and E. Nygren, "Bootstrapping TLS Encrypted ClientHello with DNS Service Bindings",
TLS Encrypted ClientHello with DNS Service Bindings", Work RFC 9848, February 2026,
in Progress, Internet-Draft, draft-ietf-tls-svcb-ech-08, <https://www.rfc-editor.org/info/rfc9848>.
16 June 2025, <https://datatracker.ietf.org/doc/html/
draft-ietf-tls-svcb-ech-08>.
Appendix A. Changes
From -12 to -13:
* Changes resulting from IESG review.
From -11 to -12:
* Changes resulting from IETF last call reviews.
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 clarification of encoding based on current OpenSSL ECH
feature branch code.
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
From -01 to -02:
* ECHO -> ECH
From -00 to -01: Acknowledgements
* ESNI -> ECHO Thanks to Daniel McCarney, Jim Reid, and Peter Yee for comments.
Author's Address Author's Address
Stephen Farrell Stephen Farrell
Trinity College Dublin Trinity College Dublin
Dublin Dublin
2 2
Ireland Ireland
Phone: +353-1-896-2354 Phone: +353-1-896-2354
Email: stephen.farrell@cs.tcd.ie Email: stephen.farrell@cs.tcd.ie
 End of changes. 27 change blocks. 
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