Tribblix: manual page: CURLOPT

CURLOPT_SSLVERSION(3) Introduction to Library Functions

NAME

CURLOPT_SSLVERSION - preferred TLS/SSL version

SYNOPSIS

#include <curl/curl.h>

CURLcode curl_easy_setopt(CURL *handle, CURLOPT_SSLVERSION, long version);

DESCRIPTION

Pass a long as parameter to control which version range of SSL/TLS
versions to use.

The SSL and TLS versions have typically developed from the most
insecure version to be more and more secure in this order through
history: SSL v2, SSLv3, TLS v1.0, TLS v1.1, TLS v1.2 and the most
recent TLS v1.3.

Use one of the available defines for this purpose. The available
options are:

CURL_SSLVERSION_DEFAULT
The default acceptable version range. The minimum acceptable
version is by default TLS v1.0 since 7.39.0 (unless the TLS
library has a stricter rule).

CURL_SSLVERSION_TLSv1
TLS v1.0 or later

CURL_SSLVERSION_SSLv2
SSL v2 - refused

CURL_SSLVERSION_SSLv3
SSL v3 - refused

CURL_SSLVERSION_TLSv1_0
TLS v1.0 or later (Added in 7.34.0)

CURL_SSLVERSION_TLSv1_1
TLS v1.1 or later (Added in 7.34.0)

CURL_SSLVERSION_TLSv1_2
TLS v1.2 or later (Added in 7.34.0)

CURL_SSLVERSION_TLSv1_3
TLS v1.3 or later (Added in 7.52.0)

The maximum TLS version can be set by using one of the
CURL_SSLVERSION_MAX_ macros below. It is also possible to OR one of
the CURL_SSLVERSION_ macros with one of the CURL_SSLVERSION_MAX_
macros.

CURL_SSLVERSION_MAX_DEFAULT
The flag defines the maximum supported TLS version by libcurl,
or the default value from the SSL library is used. libcurl
uses a sensible default maximum, which was TLS v1.2 up to
before 7.61.0 and is TLS v1.3 since then - assuming the TLS
library support it. (Added in 7.54.0)

CURL_SSLVERSION_MAX_TLSv1_0
The flag defines maximum supported TLS version as TLS v1.0.
(Added in 7.54.0)

CURL_SSLVERSION_MAX_TLSv1_1
The flag defines maximum supported TLS version as TLS v1.1.
(Added in 7.54.0)

CURL_SSLVERSION_MAX_TLSv1_2
The flag defines maximum supported TLS version as TLS v1.2.
(Added in 7.54.0)

CURL_SSLVERSION_MAX_TLSv1_3
The flag defines maximum supported TLS version as TLS v1.3.
(Added in 7.54.0)

In versions of curl prior to 7.54 the CURL_SSLVERSION_TLS options
were documented to allow only the specified TLS version, but behavior
was inconsistent depending on the TLS library.

DEFAULT

CURL_SSLVERSION_DEFAULT

PROTOCOLS

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

All TLS backends support this option.

EXAMPLE

int main(void)
{
CURL *curl = curl_easy_init();
if(curl) {
curl_easy_setopt(curl, CURLOPT_URL, "https://example.com");

/* ask libcurl to use TLS version 1.0 or later */
curl_easy_setopt(curl, CURLOPT_SSLVERSION, (long)CURL_SSLVERSION_TLSv1);

/* Perform the request */
curl_easy_perform(curl);
}
}

HISTORY

SSLv2 is disabled by default since 7.18.1. Other SSL versions
availability may vary depending on which backend libcurl has been
built to use.

SSLv3 is disabled by default since 7.39.0.

SSLv2 and SSLv3 are refused completely since curl 7.77.0

Since 8.10.0 wolfSSL is fully supported. Before 8.10.0 the MAX macros
were not supported with wolfSSL and the other macros did not set a
minimum, but restricted the TLS version to only the specified one.

Rustls support added in 8.10.0.

AVAILABILITY

Added in curl 7.1

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).