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.