CURLOPT_SSL_CIPHER_LIST(3)

NAME
CURLOPT_SSL_CIPHER_LIST - ciphers to use for TLS

SYNOPSIS
#include <curl/curl.h>

CURLcode curl_easy_setopt(CURL *handle, CURLOPT_SSL_CIPHER_LIST, char *list);

DESCRIPTION
Pass a char pointer, pointing to a null-terminated string holding the list of cipher suites to use for the TLS 1.2 (1.1, 1.0) connection. The list must be syntactically correct, it consists of one or more cipher suite strings separated by colons.

For setting TLS 1.3 ciphers see CURLOPT_TLS13_CIPHERS(3).

A valid example of a cipher list with OpenSSL is:
"ECDHE-ECDSA-AES128-GCM-SHA256:ECDHE-RSA-AES128-GCM-SHA256:"
"ECDHE-ECDSA-CHACHA20-POLY1305:ECDHE-RSA-CHACHA20-POLY1305"

For Schannel, you can use this option to set algorithms but not specific cipher suites. Refer to the ciphers lists document for algorithms.

GnuTLS has the concept of a [priority string](https://gnutls.org/manual/html_node/Priority-Strings.html) which has its own syntax and keywords. The string set via CURLOPT_SSL_CIPHER_LIST(3) directly influences the priority setting.

Find more details about cipher lists on this URL:

 https://curl.se/docs/ssl-ciphers.html

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 to disable its use again.

DEFAULT
NULL, use built-in list

PROTOCOLS
This functionality affects all TLS based protocols: HTTPS, FTPS, IMAPS, POP3S, SMTPS etc.

This option works only with the following TLS backends: GnuTLS, OpenSSL, Schannel, mbedTLS, rustls and wolfSSL

EXAMPLE
int main(void)
{
  CURL *curl = curl_easy_init();
  if(curl) {
    CURLcode res;
    curl_easy_setopt(curl, CURLOPT_URL, "https://example.com/");
    curl_easy_setopt(curl, CURLOPT_SSL_CIPHER_LIST,
                     "ECDHE-ECDSA-CHACHA20-POLY1305:"
                     "ECDHE-RSA-CHACHA20-POLY1305");
    res = curl_easy_perform(curl);
    curl_easy_cleanup(curl);
  }
}

HISTORY
OpenSSL support added in 7.9. wolfSSL support added in 7.53.0. Schannel support added in 7.61.0. mbedTLS support added in 8.8.0. Rustls support added in 8.10.0.

Since curl 8.10.0 returns CURLE_NOT_BUILT_IN when not supported.

AVAILABILITY
Added in curl 7.9

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).

SEE ALSO
CURLOPT_PROXY_SSL_CIPHER_LIST(3), CURLOPT_PROXY_TLS13_CIPHERS(3), CURLOPT_SSLVERSION(3), CURLOPT_TLS13_CIPHERS(3), CURLOPT_USE_SSL(3)