OPENSSL_INIT_CRYPTO(3)

NAME
OPENSSL_INIT_new, OPENSSL_INIT_set_config_filename, OPENSSL_INIT_set_config_appname, OPENSSL_INIT_set_config_file_flags, OPENSSL_INIT_free, OPENSSL_init_crypto, OPENSSL_cleanup, OPENSSL_thread_stop_ex, OPENSSL_thread_stop - OpenSSL initialisation and deinitialisation functions

SYNOPSIS
 #include <openssl/crypto.h>

 void OPENSSL_cleanup(void);
 int OPENSSL_init_crypto(uint64_t opts, const OPENSSL_INIT_SETTINGS *settings);
 void OPENSSL_thread_stop_ex(OSSL_LIB_CTX *ctx);
 void OPENSSL_thread_stop(void);

 OPENSSL_INIT_SETTINGS *OPENSSL_INIT_new(void);
 int OPENSSL_INIT_set_config_filename(OPENSSL_INIT_SETTINGS *init,
                                      const char* filename);
 int OPENSSL_INIT_set_config_file_flags(OPENSSL_INIT_SETTINGS *init,
                                        unsigned long flags);
 int OPENSSL_INIT_set_config_appname(OPENSSL_INIT_SETTINGS *init,
                                     const char* name);
 void OPENSSL_INIT_free(OPENSSL_INIT_SETTINGS *init);

DESCRIPTION
During normal operation OpenSSL (libcrypto) will allocate various resources at start up that must, subsequently, be freed on close down of the library. Additionally some resources are allocated on a per thread basis (if the application is multi-threaded), and these resources must be freed prior to the thread closing.

As of version 1.1.0 OpenSSL will automatically allocate all resources that it needs so no explicit initialisation is required.

However, there may be situations when explicit initialisation is desirable or needed, for example when some nondefault initialisation is required. The function OPENSSL_init_crypto() can be used for this purpose for libcrypto (see also OPENSSL_init_ssl(3) for the libssl equivalent).

Numerous internal OpenSSL functions call OPENSSL_init_crypto(). Therefore, in order to perform nondefault initialisation, OPENSSL_init_crypto() MUST be called by application code prior to any other OpenSSL function calls.

The opts parameter specifies which aspects of libcrypto should be initialised. Valid options are:

OPENSSL_INIT_NO_LOAD_CRYPTO_STRINGS
    Suppress automatic loading of the libcrypto error strings. This option is not a default option. Once selected subsequent calls to OPENSSL_init_crypto() with the option OPENSSL_INIT_LOAD_CRYPTO_STRINGS will be ignored.

OPENSSL_INIT_LOAD_CRYPTO_STRINGS
    Automatic loading of the libcrypto error strings. With this option the library will automatically load the libcrypto error strings. This option is a default option. Once selected subsequent calls to OPENSSL_init_crypto() with the option OPENSSL_INIT_NO_LOAD_CRYPTO_STRINGS will be ignored.

OPENSSL_INIT_ADD_ALL_CIPHERS
    With this option the library will automatically load and make available all libcrypto ciphers. This option is a default option. Once selected subsequent calls to OPENSSL_init_crypto() with the option OPENSSL_INIT_NO_ADD_ALL_CIPHERS will be ignored.

OPENSSL_INIT_ADD_ALL_DIGESTS
    With this option the library will automatically load and make available all libcrypto digests. This option is a default option. Once selected subsequent calls to OPENSSL_init_crypto() with the option OPENSSL_INIT_NO_ADD_ALL_DIGESTS will be ignored.

OPENSSL_INIT_NO_ADD_ALL_CIPHERS
    With this option the library will suppress automatic loading of libcrypto ciphers. This option is not a default option. Once selected subsequent calls to OPENSSL_init_crypto() with the option OPENSSL_INIT_ADD_ALL_CIPHERS will be ignored.

OPENSSL_INIT_NO_ADD_ALL_DIGESTS
    With this option the library will suppress automatic loading of libcrypto digests. This option is not a default option. Once selected subsequent calls to OPENSSL_init_crypto() with the option OPENSSL_INIT_ADD_ALL_DIGESTS will be ignored.

OPENSSL_INIT_LOAD_CONFIG
    With this option an OpenSSL configuration file will be automatically loaded and used by calling OPENSSL_config(). This is a default option. Note that in OpenSSL 1.1.1 this was the default for libssl but not for libcrypto (see OPENSSL_init_ssl(3) for further details about libssl initialisation). In OpenSSL 1.1.0 this was a nondefault option for both libssl and libcrypto. See the description of OPENSSL_INIT_new(), below.

OPENSSL_INIT_NO_LOAD_CONFIG
    With this option the loading of OpenSSL configuration files will be suppressed. It is the equivalent of calling OPENSSL_no_config(). This is not a default option.

OPENSSL_INIT_ASYNC
    With this option the library with automatically initialise the libcrypto async sub-library (see ASYNC_start_job(3)). This is a default option.

OPENSSL_INIT_ATFORK
    With this option the library will register its fork handlers. See OPENSSL_fork_prepare(3) for details.

OPENSSL_INIT_NO_ATEXIT
    The option has no effect in 4.0 and later.

Multiple options may be combined together in a single call to OPENSSL_init_crypto(). For example:

 OPENSSL_init_crypto(OPENSSL_INIT_NO_ADD_ALL_CIPHERS
                     | OPENSSL_INIT_NO_ADD_ALL_DIGESTS, NULL);

The OPENSSL_cleanup() function requests deinitialization of OpenSSL (both libcrypto and libssl). OpenSSL installs a global destructor function at initialization time if the toolchain supports this. This destructor is run after exit and after subordinate library destructors have run. By default the destructor does nothing. If deinitialization has been requested by a call to OPENSSL_cleanup(), then the destructor frees all global resources allocated by OpenSSL.

If the toolchain building OpenSSL does not support a global destructor, by default OPENSSL_cleanup will do nothing, as this is the safest option, allowing the operating system to then reap all library resources on process exit. Note, this may, on some leak detection tools (like valgrind) result in reports that indicate reachable memory remains on exit in certain configurations. As these are not formally leaks, it is recommended that reachable memory reports be suppressed when running such tools.

If OpenSSL is compiled with the compile time option of DO_NOT_SKIP_OPENSSL_CLEANUP OPENSSL_cleanup() will deinitialize the library immediately when called. This is not normally recommended unless you are certain that the global resources will not be used by something after the point at which OPENSSL_cleanup() is called.

Once OPENSSL_cleanup() has been called the library cannot be reinitialised. Attempts to call OPENSSL_init_crypto() will fail and an ERR_R_INIT_FAIL error will be added to the error stack. Note that because initialisation has failed OpenSSL error strings will not be available, only an error code. This code can be put through the openssl errstr command line application to produce a human readable error (see openssl-errstr(1)).

The OPENSSL_thread_stop_ex() function deallocates resources associated with the current thread for the given OSSL_LIB_CTX ctx. The ctx parameter can be NULL in which case the default OSSL_LIB_CTX is used.

Typically, this function will be called automatically by the library when the thread exits as long as the OSSL_LIB_CTX has not been freed before the thread exits. If OSSL_LIB_CTX_free() is called OPENSSL_thread_stop_ex will be called automatically for the current thread (but not any other threads that may have used this OSSL_LIB_CTX).

OPENSSL_thread_stop_ex should be called on all threads that will exit after the OSSL_LIB_CTX is freed. Typically this is not necessary for the default OSSL_LIB_CTX (because all resources are cleaned up on library exit) except if thread local resources should be freed before library exit, or under the circumstances described in the NOTES section below.

OPENSSL_thread_stop() is the same as OPENSSL_thread_stop_ex() except that the default OSSL_LIB_CTX is always used.

The OPENSSL_INIT_LOAD_CONFIG flag will load a configuration file, as with CONF_modules_load_file(3) with, by default, NULL filename and application name and the CONF_MFLAGS_IGNORE_MISSING_FILE, CONF_MFLAGS_IGNORE_RETURN_CODES and CONF_MFLAGS_DEFAULT_SECTION flags. The filename, application name, and flags can be customized by providing a non-null OPENSSL_INIT_SETTINGS object. The object can be allocated via OPENSSL_INIT_new(). The OPENSSL_INIT_set_config_filename() function can be used to specify a nondefault filename, which is copied and need not refer to persistent storage. Similarly, OPENSSL_INIT_set_config_appname() can be used to specify a nondefault application name. Finally, OPENSSL_INIT_set_file_flags can be used to specify nondefault flags. If the CONF_MFLAGS_IGNORE_RETURN_CODES flag is not included, any errors in the configuration file will cause an error return from OPENSSL_init_crypto or indirectly OPENSSL_init_ssl(3). The object can be released with OPENSSL_INIT_free() when done. If the argument to OPENSSL_INIT_free() is NULL, nothing is done.

NOTES
Resources local to a thread are deallocated automatically when the thread exits (e.g. in a pthreads environment, when pthread_exit() is called). On Windows platforms this is done in response to a DLL_THREAD_DETACH message being sent to the libcrypto32.dll entry point. Some windows functions may cause threads to exit without sending this message (for example ExitProcess()). If the application uses such functions, then the application must free up OpenSSL resources directly via a call to OPENSSL_thread_stop() on each thread. Similarly this message will also not be sent if OpenSSL is linked statically, and therefore applications using static linking should also call OPENSSL_thread_stop() on each thread. Additionally if OpenSSL is loaded dynamically via LoadLibrary() and the threads are not destroyed until after FreeLibrary() is called then each thread should call OPENSSL_thread_stop() prior to the FreeLibrary() call.

On Linux/Unix where OpenSSL has been loaded via dlopen() and the application is multi-threaded and if dlclose() is subsequently called prior to the threads being destroyed then OpenSSL will not be able to deallocate resources associated with those threads. The application should either call OPENSSL_thread_stop() on each thread prior to the dlclose() call, or alternatively the original dlopen() call should use the RTLD_NODELETE flag (where available on the platform).

RETURN VALUES
The functions OPENSSL_init_crypto, and OPENSSL_INIT_set_config_appname() return 1 on success or 0 on error.

SEE ALSO
OPENSSL_init_ssl(3)

HISTORY
The OPENSSL_init_crypto(), OPENSSL_cleanup() OPENSSL_thread_stop(), OPENSSL_INIT_new(), OPENSSL_INIT_set_config_appname() and OPENSSL_INIT_free() functions were added in OpenSSL 1.1.0.

OPENSSL_INIT_ENGINE_RDRAND, OPENSSL_INIT_ENGINE_DYNAMIC, OPENSSL_INIT_ENGINE_OPENSSL, OPENSSL_INIT_ENGINE_CRYPTODEV, OPENSSL_INIT_ENGINE_CAPI, OPENSSL_INIT_ENGINE_PADLOCK, OPENSSL_INIT_ENGINE_AFALG OPENSSL_init_crypto() opts were removed in OpenSSL 4.0.

OPENSSL_INIT_ENGINE_ALL_BUILTIN is defined to 0 since OpenSSL 4.0.

COPYRIGHT
Copyright 2016-2026 The OpenSSL Project Authors. All Rights Reserved.

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>.