SSL_CTX_config¶

NAME¶

SSL_CTX_config, SSL_config - configure SSL_CTX or SSL structure

SYNOPSIS¶

#include <openssl/ssl.h>

int SSL_CTX_config(SSL_CTX *ctx, const char *name);
int SSL_config(SSL *s, const char *name);

DESCRIPTION¶

The functions SSL_CTX_config() and SSL_config() apply additional configuration settings to an SSL_CTX or SSL structure using the configuration name. The name must match a parameter in the configuration file's ssl module section, whose value is the name of another section with SSL configuration commands. See SSL_CONF_cmd(3) for a description of the available commands.

By calling SSL_CTX_config() or SSL_config() an application can perform many complex tasks based on the contents of the configuration file: greatly simplifying application configuration code. Some future-proofing can be attained this way: the specified configuration section can specify settings supported by the run-time version of OpenSSL that were not known at the time the application code was written.

A configuration file must have been previously loaded, for example using CONF_modules_load_file(3). See config(5) for details of the configuration file syntax. In most applications the default openssl.cnf file is loaded automatically as part of library initialisation.

RETURN VALUES¶

SSL_CTX_config() and SSL_config() return 1 for success or 0 if an error occurred.

EXAMPLES¶

If, for example, the loaded configuration file contains the following:

# Top level "default" section, if no application name was specified as part
# initialisation, it defaults to "openssl_conf".
openssl_conf = openssl_init

[openssl_init]
# SSL module initialisation
ssl_conf = ssl_init

[ssl_init]
system_default = default_ssl_settings
tweaks_for_tls12 = tls12_custom_settings
tweaks_for_tls13 = tls13_custom_settings

[default_ssl_settings]
MinProtocol = TLSv1.2
# Defaults are typically the wisest choice, override only with good cause.
MinProtocol = ...
Ciphers = ...
Groups = ...
SignatureAlgorithms = ...

[tls12_custom_settings]
# Defaults are typically the wisest choice, override only with good cause.
MaxProtocol = TLSv1.2
...

[tls13_custom_settings]
# Defaults are typically the wisest choice, override only with good cause.
MinProtocol = TLSv1.3
...

An application that wants to only use "TLS 1.2" might call:

/* Initialised per "system_default" settings */
if ((ctx = SSL_CTX_new(TLS_server_method())) == NULL) {
    fprintf(stderr, "Error creating the SSL context.\n");
    goto err;
}

/*
 * Further tweaks per the "ssl" module "tweaks_for_tls12" setting, i.e. the
 * configuration file's "tls12_custom_settings" section.
 */
if (SSL_CTX_config(ctx, "tweaks_for_tls12") == 0) {
    fprintf(stderr, "Error applying 'tweaks_for_tls12' context configuration.\n");
    goto err;
}

The setting of the protocol version ceiling and any other settings relevant to TLS 1.2 are in the configuration file, and don't need to be hard-coded in the application. Similarly, using tweaks_for_tls13 as the configuration name applies the corresponding settings from the "tls13_custom_settings" section (per the SSL module tweaks_for_tls13 parameter).

HISTORY¶

The SSL_CTX_config() and SSL_config() functions were added in OpenSSL 1.1.0.

COPYRIGHT¶

Licensed under the Apache License 2.0 (the "License"). You may not use this file except in compliance with the License. You can obtain a copy in the file LICENSE in the source distribution or at https://www.openssl.org/source/license.html.