<?xmlversion="1.0" encoding="US-ASCII"?> <!-- this is version 5 of this xml2rfc template -->version='1.0' encoding='UTF-8'?> <!DOCTYPE rfcSYSTEM "rfc2629.dtd"[ <!ENTITYrfc2119 SYSTEM "https://xml.resource.org/public/rfc/bibxml/reference.RFC.2119.xml">nbsp " "> <!ENTITYrfc4648 SYSTEM "https://xml.resource.org/public/rfc/bibxml/reference.RFC.4648.xml">zwsp "​"> <!ENTITYrfc7468 SYSTEM "https://xml.resource.org/public/rfc/bibxml/reference.RFC.7468.xml">nbhy "‑"> <!ENTITYrfc8174 SYSTEM "https://xml.resource.org/public/rfc/bibxml/reference.RFC.8174.xml"> <!ENTITY rfc8446 SYSTEM "https://xml.resource.org/public/rfc/bibxml/reference.RFC.8446.xml"> <!ENTITY rfc8446 SYSTEM "https://xml.resource.org/public/rfc/bibxml/reference.RFC.9460.xml"> <!ENTITY I-D.ietf-tls-esni SYSTEM "http://xml.resource.org/public/rfc/bibxml3/reference.I-D.ietf-tls-esni"> <!ENTITY I-D.ietf-tls-svcb-ech SYSTEM "http://xml.resource.org/public/rfc/bibxml3/reference.I-D.ietf-tls-svcb-ech">wj "⁠"> ]><?rfc toc="yes"?> <?rfc symrefs="yes"?> <?rfc compact="yes"?> <?rfc subcompact="yes"?> <?rfc strict="no"?> <?rfc rfcedstyle="yes"?> <?rfc comments="yes"?> <?rfc inline="yes"?><rfc xmlns:xi="http://www.w3.org/2001/XInclude" category="std" docName="draft-farrell-tls-pemesni-13" number="9934" ipr="trust200902">obsoletes="" updates="" submissionType="IETF" xml:lang="en" tocInclude="true" symRefs="true" sortRefs="true" version="3" consensus="true"> <front><title abbrev="PEM<!-- [rfced] Please note that we have expanded the abbreviations in the title of the document. Please let us know any concerns. Original: PEM file format forECH">PEM file formatECH Current: Privacy-Enhanced Mail (PEM) File Format forECH</title>Encrypted ClientHello (ECH) --> <title abbrev="PEM File Format for ECH">Privacy-Enhanced Mail (PEM) File Format for Encrypted ClientHello (ECH)</title> <seriesInfo name="RFC" value="9934"/> <author fullname="Stephen Farrell" initials="S." surname="Farrell"> <organization>Trinity College Dublin</organization> <address> <postal><street/><city>Dublin</city><region/><code>2</code> <country>Ireland</country> </postal> <phone>+353-1-896-2354</phone> <email>stephen.farrell@cs.tcd.ie</email> </address> </author> <date month="February" year="2026"/> <!-- [rfced] FYI - The submitted XML had the area set to "Security Area". Is this correct? --> <area>Security Area</area><workgroup>Internet Engineering Task Force (IETF)</workgroup><keyword>TLS</keyword> <keyword>ESNI</keyword> <abstract> <t> Encrypted ClientHello (ECH) key pairs need to be configured into TLS servers, which can be built using different TLS libraries. This document specifies a standard file formatto use,for this purpose, similar to how RFC 7468 defines otherPEMPrivacy-Enhanced Mail (PEM) file formats. </t> </abstract> </front> <middle> <sectiontitle="Introduction">numbered="true" toc="default"> <name>Introduction</name> <t>Encrypted ClientHello (ECH) <xreftarget="I-D.ietf-tls-esni"/>target="RFC9849" format="default"/> for TLS1.3 <xreftarget="RFC8446"/>target="RFC8446" format="default"/> 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 <xreftarget="RFC9460"/>target="RFC9460" format="default"/> 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 <xreftarget="RFC7468"/>.target="RFC7468" format="default"/>. </t> </section> <sectiontitle="Terminology"> <t>Thenumbered="true" toc="default"> <name>Terminology</name> <t> The key words"MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", "SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY","<bcp14>MUST</bcp14>", "<bcp14>MUST NOT</bcp14>", "<bcp14>REQUIRED</bcp14>", "<bcp14>SHALL</bcp14>", "<bcp14>SHALL NOT</bcp14>", "<bcp14>SHOULD</bcp14>", "<bcp14>SHOULD NOT</bcp14>", "<bcp14>RECOMMENDED</bcp14>", "<bcp14>NOT RECOMMENDED</bcp14>", "<bcp14>MAY</bcp14>", and"OPTIONAL""<bcp14>OPTIONAL</bcp14>" in this document are to be interpreted as described inBCP 14BCP 14 <xref target="RFC2119"/> <xref target="RFC8174"/> when, and only when, they appear in all capitals, as shownhere.</t>here. </t> </section> <sectiontitle="ECHConfig file">numbered="true" toc="default"> <name>ECHConfig File</name> <t>A PEM ECH file contains zero or one private key and one encoded ECHConfigList.</t> <t>The public and private keysMUST<bcp14>MUST</bcp14> both be PEM encoded <xreftarget="RFC7468"/>.target="RFC7468" format="default"/>. The 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 an ECHConfigList. When a private key is present, the ECHConfigListMUST<bcp14>MUST</bcp14> contain an ECHConfig that matches the private key. The private keyMUST<bcp14>MUST</bcp14> be encoded as a PKCS#8 PrivateKey <xreftarget="RFC7468"/>.target="RFC7468" format="default"/>. The public key(s)MUST<bcp14>MUST</bcp14> be thebase64 encodedbase64-encoded form (seeSection 4 of<xreftarget="RFC4648"/>) formtarget="RFC4648" section="4"/>) of an ECHConfigList value that can be published in the DNS using an HTTPS RR as described in <xreftarget="I-D.ietf-tls-svcb-ech"/>.target="RFC9848" format="default"/>. The string "ECHCONFIG"MUST<bcp14>MUST</bcp14> be used in the PEM file delimiter for the public key.</t> <t>Any content after the PEM encoded ECHConfigListSHOULD<bcp14>SHOULD</bcp14> be ignored.</t> <t><xreftarget="sample"/>target="sample" format="default"/> shows an example ECHConfig PEM File</t> <figureanchor="sample" title="Exampleanchor="sample"> <name>Example ECHConfig PEMfile" > <artwork><![CDATA[File</name> <artwork name="" type="" align="left" alt=""><![CDATA[ -----BEGIN PRIVATE KEY----- MC4CAQAwBQYDK2VuBCIEICjd4yGRdsoP9gU7YT7My8DHx1Tjme8GYDXrOMCi8v1V -----END PRIVATE KEY----- -----BEGIN ECHCONFIG----- AD7+DQA65wAgACA8wVN2BtscOl3vQheUzHeIkVmKIiydUhDCliA4iyQRCwAEAAEA AQALZXhhbXBsZS5jb20AAA== -----ENDECHCONFIG----- ]]></artwork>ECHCONFIG-----]]></artwork> </figure> <t> If the above ECHConfigList were published in the DNS for foo.example.com, then one could access that as shown in <xreftarget="dig"/>.target="dig" format="default"/>. </t> <figureanchor="dig" title="Useanchor="dig"> <name>Use ofdigDig togetGet the ECHConfigList fromDNS" > <artwork><![CDATA[DNS</name> <artwork name="" type="" align="left" alt=""><![CDATA[ $ dig +short HTTPS foo.example.com 1 . ech=AD7+DQA65wAgACA8wVN2BtscOl3vQheUzHeIkVmKIiydUhDCliA4iyQRwAEAAEAAQALZXhhbXBsZS5jb20AAA== ]]></artwork>wAEAAEAAQALZXhhbXBsZS5jb20AAA==]]></artwork> </figure> <t> TLS servers using this file format might configure multiple file names as part of their overall configuration, if, for example, only the ECHConfigList values from a subset of those files are to be used as the value for retry_configs in the ECH fallback scenario. </t> <t> The ECHConfigList in a PEM file might contain more than one ECHConfig if, for example, those ECHConfig values contain different extensions or different public_name values. Consistent with <xreftarget="I-D.ietf-tls-esni"/>,target="RFC9849" format="default"/>, the ECHConfig values within an ECHConfigList appear in decreasing order of preference. If the ECHConfigList value is to be used as the retry_configs value, then that might contain different public keys. (Nonetheless, when a private key is present, thatMUST<bcp14>MUST</bcp14> match the public key from one of the ECHConfig values.) </t> </section> <sectiontitle="Security Considerations">numbered="true" toc="default"> <name>Security Considerations</name> <t>Storing cryptographic keys in files leaves them vulnerable should anyone get read access to the filesystem on which they are stored. The same protection mechanisms that would be used for a server'sPEM encodedPEM-encoded HTTPS certificate private key should be used for the PEM ECH configuration. </t> <t> The security considerations of <xreftarget="I-D.ietf-tls-svcb-ech"/>target="RFC9848" format="default"/> apply when retrieving an ECHConfigList from the DNS. </t> <t> For clarity, only the ECHConfigList is to be published in the DNS - the private key from an ECH PEM fileMUST NOT<bcp14>MUST NOT</bcp14> be published in the DNS. </t> </section> <sectiontitle="Acknowledgements"> <t>Thanks to Daniel McCarney, Jim Reid and Peter Yee for comments.</t> </section> <section title="IANA Considerations">numbered="true" toc="default"> <name>IANA Considerations</name> <t>This documentcontainshas no IANAconsiderations.</t>actions.</t> </section> </middle> <back><references title="Normative References"> <?rfc include='reference.RFC.2119'?> <?rfc include='reference.RFC.4648'?> <?rfc include='reference.RFC.7468'?> <?rfc include='reference.RFC.8174'?> <?rfc include='reference.RFC.8446'?> &I-D.ietf-tls-esni; </references> <references title="Informative References"> <?rfc include='reference.RFC.9460'?> &I-D.ietf-tls-svcb-ech; </references><references> <name>References</name> <references> <name>Normative References</name> <xi:include href="https://bib.ietf.org/public/rfc/bibxml/reference.RFC.2119.xml"/> <xi:include href="https://bib.ietf.org/public/rfc/bibxml/reference.RFC.4648.xml"/> <xi:include href="https://bib.ietf.org/public/rfc/bibxml/reference.RFC.7468.xml"/> <xi:include href="https://bib.ietf.org/public/rfc/bibxml/reference.RFC.8174.xml"/> <xi:include href="https://bib.ietf.org/public/rfc/bibxml/reference.RFC.8446.xml"/> <!--<section title="Change Log "> <t>[[RFC editor: please remove this before publication.]]</t> <t>From -00 to -01: <list style="symbols"> <t>Re-structured a bit after re-reading rfc8615</t> </list> </t> </section>[I-D.ietf-tls-esni] -> [RFC9849] in AUTH48 as of 02/17/26 --><section title="Changes"> <t>From -12 to -13: <list style="symbols"> <t>Changes resulting from IESG review.</t> </list> </t> <t>From -11 to -12: <list style="symbols"> <t>Changes resulting from IETF last call reviews.</t> </list> </t> <t>From -10 to -11: <list style="symbols"> <t>Change to standards track<reference anchor="RFC9849" target="https://www.rfc-editor.org/info/rfc9849"> <front> <title>TLS Encrypted Client Hello</title> <author initials="E." surname="Rescorla" fullname="Eric Rescorla"> <organization>Independent</organization> </author> <author initials="K." surname="Oku" fullname="Kazuho Oku"> <organization>Fastly</organization> </author> <author initials="N." surname="Sullivan" fullname="Nick Sullivan"> <organization>Cryptography Consulting LLC</organization> </author> <author initials="C. A." surname="Wood" fullname="Christopher A. Wood"> <organization>Cloudflare</organization> </author> <date month='February' year='2026'/> </front> <seriesInfo name="RFC" value="9849"/> <seriesInfo name="DOI" value="10.17487/RFC9849"/> </reference> </references> <references> <name>Informative References</name> <xi:include href="https://bib.ietf.org/public/rfc/bibxml/reference.RFC.9460.xml"/> <!-- [I-D.ietf-tls-svcb-ech] RFC-to-be 9848 in AUTH48-DONE asagreedof 02/17/2026 --> <reference anchor="RFC9848" target="https://www.rfc-editor.org/info/rfc9848"> <front> <title> Bootstrapping TLS Encrypted ClientHello withshepherd/AD.</t> </list> </t> <t>From -09 to -10: <list style="symbols"> <t>Tweaks to fit being AD sponsored.</t> </list> </t> <t>From -08DNS Service Bindings </title> <author fullname="Benjamin M. Schwartz" initials="B. M." surname="Schwartz"> <organization>Meta Platforms, Inc.</organization> </author> <author fullname="Mike Bishop" initials="M." surname="Bishop"> <organization>Akamai Technologies</organization> </author> <author fullname="Erik Nygren" initials="E." surname="Nygren"> <organization>Akamai Technologies</organization> </author> <date month="February" year="2026"/> </front> <seriesInfo name="RFC" value="9848"/> </reference> </references> </references> <section numbered="false" toc="default"> <name>Acknowledgements</name> <t>Thanks to-09: <list style="symbols"> <t>Minor clarification<contact fullname="Daniel McCarney"/>, <contact fullname="Jim Reid"/>, and <contact fullname="Peter Yee"/> for comments.</t> </section> <!-- [rfced] Please review the "Inclusive Language" portion ofencoding based on current OpenSSL ECH feature branch code.</t> </list> </t> <t>From -07 to -08: <list style="symbols"> <t>Processed some github comments</t> </list> </t> <t>From -06 to -07: <list style="symbols"> <t>Refresh due to expiry.</t> </list> </t> <t>From -05 to -06: <list style="symbols"> <t>Refresh due to expiry.</t> </list> </t> <t>From -04 to -05: <list style="symbols"> <t>Refresh due to expiry.</t> </list> </t> <t>From -03 to -04: <list style="symbols"> <t>Refresh due to expiry.</t> </list> </t> <t>From -02 to -03: <list style="symbols"> <t>Refresh due to expirythe online Style Guide <https://www.rfc-editor.org/styleguide/part2/#inclusive_language> and let us know if any changes are needed. Updates of this nature typically result in more precise language, which is helpful for readers. Note that our script did notpossible ISE destination</t> </list> </t> <t>From -01 to -02: <list style="symbols"> <t>ECHO -> ECH</t> </list> </t> <t>From -00 to -01: <list style="symbols"> <t>ESNI -> ECHO</t> </list> </t> </section>flag any words in particular, but this should still be reviewed as a best practice. --> </back> </rfc>