]> Trinity College Dublin

Dublin 2 Ireland +353-1-896-2354 stephen.farrell@cs.tcd.ie

Security Area TLS TLS ESNI 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.

Encrypted ClientHello (ECH) for TLS1.3 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 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 . [[This idea could: a) wither on the vine, b) be published as it's own RFC, or c) end up as a PR for . 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.]]

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 when, and only when, they appear in all capitals, as shown here.

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. shows an example ECHConfig PEM File

Storing cryptographic keys in files leaves them vulnerable should anyone get shell access to the TLS server machine. So: Don't let that happen:-)

TBD, as needed

There are none so this section can be deleted later.

&I-D.ietf-tls-esni; &I-D.ietf-dnsop-svcb-https;

From -01 to -02: ECHO -> ECH From -00 to -01: ESNI -> ECHO