CURLOPT_SSL_EC_CURVES - key exchange curves

Added in curl 7.73.0

"", embedded in SSL backend

Pass a string as parameter with a colon delimited list of Elliptic curve (EC) algorithms. This option defines the client's key exchange algorithms in the SSL handshake (if the SSL backend libcurl is built to use supports it). 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 restore back to internal default.

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_EC_CURVES, "X25519:P-521"); res = curl_easy_perform(curl); curl_easy_cleanup(curl); } }

CURLOPT_SSL_EC_CURVES - key exchange curves

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

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).

CURLOPT_SSL_CIPHER_LIST(3), CURLOPT_SSL_OPTIONS(3), CURLOPT_TLS13_CIPHERS(3) libcurl 2025-06-16 CURLOPT_SSL_EC_CURVES(3)

#include <curl/curl.h> CURLcode curl_easy_setopt(CURL *handle, CURLOPT_SSL_EC_CURVES, char *list);