---
c: Copyright (C) Daniel Stenberg, <daniel@haxx.se>, et al.
SPDX-License-Identifier: curl
Title: CURLOPT_ECH
Section: 3
Source: libcurl
See-also:
  - CURLOPT_DOH_URL (3)
Protocol:
  - TLS
TLS-backend:
  - OpenSSL
  - wolfSSL
  - Rustls
Added-in: 8.8.0
---

# NAME

CURLOPT_ECH - configuration for Encrypted Client Hello

# SYNOPSIS

~~~c
#include <curl/curl.h>

CURLcode curl_easy_setopt(CURL *handle, CURLOPT_ECH, char *config);
~~~

# DESCRIPTION

This feature is **experimental** and may change before it is considered
stable. We advise against using it in production.

ECH is only compatible with TLSv1.3.

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:

## false

Turns off ECH.

## grease

Instructs client to emit a GREASE ECH extension. (The connection fails if ECH
is attempted but fails.)

## true

Instructs client to attempt ECH, if possible, but to not fail if attempting
ECH is not possible.

## hard

Instructs client to attempt ECH and fail if attempting ECH is not possible.

## ecl:\<base64-value\>

If the string starts with `ecl:` 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.

## pn:\<name\>

If the string starts with `pn:` 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.

##

The application does not have to keep the string around after setting this
option.

Using this option multiple times makes the last set string override the
previous ones. Set it to NULL or "false" to disable its use again.

# DEFAULT

NULL, meaning ECH is disabled.

# %PROTOCOLS%

# EXAMPLE

~~~c
int main(void)
{
  CURL *curl = curl_easy_init();

  static const char *config =
    "ecl:AED+DQA87wAgACB/RuzUCsW3uBbSFI7mzD63TUXpI8sGDTnFTbFCDpa+"
    "CAAEAAEAAQANY292ZXIuZGVmby5pZQAA";
  if(curl) {
    CURLcode result;
    curl_easy_setopt(curl, CURLOPT_ECH, config);
    result = curl_easy_perform(curl);
    curl_easy_cleanup(curl);
  }
}
~~~
# %AVAILABILITY%

# RETURN VALUE

curl_easy_setopt(3) returns a CURLcode indicating success or error.

CURLE_OK (0) means everything was OK, non-zero means an error occurred, see
libcurl-errors(3).
