Internet-Draft PEM file format for ECH May 2022
Farrell Expires 23 November 2022 [Page]
Intended Status:
S. Farrell
Trinity College Dublin

PEM file format for ECH


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

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This Internet-Draft will expire on 23 November 2022.

Table of Contents

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].

[[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 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

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

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

Bradner, S., "Key words for use in RFCs to Indicate Requirement Levels", BCP 14, RFC 2119, DOI 10.17487/RFC2119, , <>.
Josefsson, S. and S. Leonard, "Textual Encodings of PKIX, PKCS, and CMS Structures", RFC 7468, DOI 10.17487/RFC7468, , <>.
Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC 2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174, , <>.
Rescorla, E., "The Transport Layer Security (TLS) Protocol Version 1.3", RFC 8446, DOI 10.17487/RFC8446, , <>.
Rescorla, E., Oku, K., Sullivan, N., and C. A. Wood, "TLS Encrypted Client Hello", Work in Progress, Internet-Draft, draft-ietf-tls-esni-14, , <>.
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-09, , <>.

Appendix A. Changes

From -02 to -03:

From -01 to -02:

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Author's Address

Stephen Farrell
Trinity College Dublin