.\" generated by cd2nroff 0.1 from CURLOPT_ECH.md
.TH CURLOPT_ECH 3 "2024-11-18" libcurl
.SH NAME
CURLOPT_ECH \- configuration for Encrypted Client Hello
.SH SYNOPSIS
.nf
#include <curl/curl.h>

CURLcode curl_easy_setopt(CURL *handle, CURLOPT_ECH, char *config);
.fi
.SH DESCRIPTION
ECH is only compatible with TLSv1.3.

This experimental feature requires a special build of OpenSSL, as ECH is not
yet supported in OpenSSL releases. In contrast ECH is supported by the latest
BoringSSL and wolfSSL releases.

There is also a known issue with using wolfSSL which does not support ECH when
the HelloRetryRequest mechanism is used.

Pass a string that specifies configuration details for ECH. In all cases, if
ECH is attempted, it may fail for various reasons. The keywords supported are:
.IP false
Turns off ECH.
.IP grease
Instructs client to emit a GREASE ECH extension. (The connection fails if ECH
is attempted but fails.)
.IP true
Instructs client to attempt ECH, if possible, but to not fail if attempting
ECH is not possible.
.IP hard
Instructs client to attempt ECH and fail if attempting ECH is not possible.
.IP ecl:\<base64-value\>
If the string starts with \fIecl:\fP then the remainder of the string should be a
base64\-encoded ECHConfigList that is used for ECH rather than attempting to
download such a value from the DNS.
.IP pn:\<name\>
If the string starts with \fIpn:\fP then the remainder of the string should be a
DNS/hostname that is used to over\-ride the public_name field of the
ECHConfigList that is used for ECH.
.SH DEFAULT
NULL, meaning ECH is disabled.
.SH PROTOCOLS
This functionality affects all TLS based protocols: HTTPS, FTPS, IMAPS, POP3S, SMTPS etc.

This option works only with the following TLS backends:
OpenSSL and wolfSSL
.SH EXAMPLE
.nf
CURL *curl = curl_easy_init();

const char *config ="ecl:AED+DQA87wAgACB/RuzUCsW3uBbSFI7mzD63TUXpI8sGDTnFTbFCDpa+CAAEAAEAAQANY292ZXIuZGVmby5pZQAA";
if(curl) {
  curl_easy_setopt(curl, CURLOPT_ECH, config);
  curl_easy_perform(curl);
}
.fi
.SH AVAILABILITY
Added in curl 8.8.0
.SH RETURN VALUE
Returns CURLE_OK on success or CURLE_OUT_OF_MEMORY if there was insufficient
heap space.
.SH SEE ALSO
.BR CURLOPT_DOH_URL (3)