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ENGINE_ADD(3)			    OpenSSL			 ENGINE_ADD(3)

NAME
       ENGINE_get_DH, ENGINE_get_DSA, ENGINE_by_id, ENGINE_get_cipher_engine,
       ENGINE_get_default_DH, ENGINE_get_default_DSA, ENGINE_get_default_RAND,
       ENGINE_get_default_RSA, ENGINE_get_digest_engine, ENGINE_get_first,
       ENGINE_get_last,	ENGINE_get_next, ENGINE_get_prev, ENGINE_new,
       ENGINE_get_ciphers, ENGINE_get_ctrl_function, ENGINE_get_digests,
       ENGINE_get_destroy_function, ENGINE_get_finish_function,
       ENGINE_get_init_function, ENGINE_get_load_privkey_function,
       ENGINE_get_load_pubkey_function,	ENGINE_load_private_key,
       ENGINE_load_public_key, ENGINE_get_RAND,	ENGINE_get_RSA,	ENGINE_get_id,
       ENGINE_get_name,	ENGINE_get_cmd_defns, ENGINE_get_cipher,
       ENGINE_get_digest, ENGINE_add, ENGINE_cmd_is_executable,	ENGINE_ctrl,
       ENGINE_ctrl_cmd,	ENGINE_ctrl_cmd_string,	ENGINE_finish, ENGINE_free,
       ENGINE_get_flags, ENGINE_init, ENGINE_register_DH, ENGINE_register_DSA,
       ENGINE_register_RAND, ENGINE_register_RSA,
       ENGINE_register_all_complete, ENGINE_register_ciphers,
       ENGINE_register_complete, ENGINE_register_digests, ENGINE_remove,
       ENGINE_set_DH, ENGINE_set_DSA, ENGINE_set_RAND, ENGINE_set_RSA,
       ENGINE_set_ciphers, ENGINE_set_cmd_defns, ENGINE_set_ctrl_function,
       ENGINE_set_default, ENGINE_set_default_DH, ENGINE_set_default_DSA,
       ENGINE_set_default_RAND,	ENGINE_set_default_RSA,
       ENGINE_set_default_ciphers, ENGINE_set_default_digests,
       ENGINE_set_default_string, ENGINE_set_destroy_function,
       ENGINE_set_digests, ENGINE_set_finish_function, ENGINE_set_flags,
       ENGINE_set_id, ENGINE_set_init_function,
       ENGINE_set_load_privkey_function, ENGINE_set_load_pubkey_function,
       ENGINE_set_name,	ENGINE_up_ref, ENGINE_get_table_flags, ENGINE_cleanup,
       ENGINE_load_builtin_engines, ENGINE_register_all_DH,
       ENGINE_register_all_DSA,	ENGINE_register_all_RAND,
       ENGINE_register_all_RSA,	ENGINE_register_all_ciphers,
       ENGINE_register_all_digests, ENGINE_set_table_flags,
       ENGINE_unregister_DH, ENGINE_unregister_DSA, ENGINE_unregister_RAND,
       ENGINE_unregister_RSA, ENGINE_unregister_ciphers,
       ENGINE_unregister_digests - ENGINE cryptographic	module support

SYNOPSIS
	#include <openssl/engine.h>

	ENGINE *ENGINE_get_first(void);
	ENGINE *ENGINE_get_last(void);
	ENGINE *ENGINE_get_next(ENGINE *e);
	ENGINE *ENGINE_get_prev(ENGINE *e);

	int ENGINE_add(ENGINE *e);
	int ENGINE_remove(ENGINE *e);

	ENGINE *ENGINE_by_id(const char	*id);

	int ENGINE_init(ENGINE *e);
	int ENGINE_finish(ENGINE *e);

	void ENGINE_load_builtin_engines(void);

	ENGINE *ENGINE_get_default_RSA(void);
	ENGINE *ENGINE_get_default_DSA(void);
	ENGINE *ENGINE_get_default_DH(void);
	ENGINE *ENGINE_get_default_RAND(void);
	ENGINE *ENGINE_get_cipher_engine(int nid);
	ENGINE *ENGINE_get_digest_engine(int nid);

	int ENGINE_set_default_RSA(ENGINE *e);
	int ENGINE_set_default_DSA(ENGINE *e);
	int ENGINE_set_default_DH(ENGINE *e);
	int ENGINE_set_default_RAND(ENGINE *e);
	int ENGINE_set_default_ciphers(ENGINE *e);
	int ENGINE_set_default_digests(ENGINE *e);
	int ENGINE_set_default_string(ENGINE *e, const char *list);

	int ENGINE_set_default(ENGINE *e, unsigned int flags);

	unsigned int ENGINE_get_table_flags(void);
	void ENGINE_set_table_flags(unsigned int flags);

	int ENGINE_register_RSA(ENGINE *e);
	void ENGINE_unregister_RSA(ENGINE *e);
	void ENGINE_register_all_RSA(void);
	int ENGINE_register_DSA(ENGINE *e);
	void ENGINE_unregister_DSA(ENGINE *e);
	void ENGINE_register_all_DSA(void);
	int ENGINE_register_DH(ENGINE *e);
	void ENGINE_unregister_DH(ENGINE *e);
	void ENGINE_register_all_DH(void);
	int ENGINE_register_RAND(ENGINE	*e);
	void ENGINE_unregister_RAND(ENGINE *e);
	void ENGINE_register_all_RAND(void);
	int ENGINE_register_ciphers(ENGINE *e);
	void ENGINE_unregister_ciphers(ENGINE *e);
	void ENGINE_register_all_ciphers(void);
	int ENGINE_register_digests(ENGINE *e);
	void ENGINE_unregister_digests(ENGINE *e);
	void ENGINE_register_all_digests(void);
	int ENGINE_register_complete(ENGINE *e);
	int ENGINE_register_all_complete(void);

	int ENGINE_ctrl(ENGINE *e, int cmd, long i, void *p, void (*f)(void));
	int ENGINE_cmd_is_executable(ENGINE *e,	int cmd);
	int ENGINE_ctrl_cmd(ENGINE *e, const char *cmd_name,
			    long i, void *p, void (*f)(void), int cmd_optional);
	int ENGINE_ctrl_cmd_string(ENGINE *e, const char *cmd_name, const char *arg,
				   int cmd_optional);

	ENGINE *ENGINE_new(void);
	int ENGINE_free(ENGINE *e);
	int ENGINE_up_ref(ENGINE *e);

	int ENGINE_set_id(ENGINE *e, const char	*id);
	int ENGINE_set_name(ENGINE *e, const char *name);
	int ENGINE_set_RSA(ENGINE *e, const RSA_METHOD *rsa_meth);
	int ENGINE_set_DSA(ENGINE *e, const DSA_METHOD *dsa_meth);
	int ENGINE_set_DH(ENGINE *e, const DH_METHOD *dh_meth);
	int ENGINE_set_RAND(ENGINE *e, const RAND_METHOD *rand_meth);
	int ENGINE_set_destroy_function(ENGINE *e, ENGINE_GEN_INT_FUNC_PTR destroy_f);
	int ENGINE_set_init_function(ENGINE *e,	ENGINE_GEN_INT_FUNC_PTR	init_f);
	int ENGINE_set_finish_function(ENGINE *e, ENGINE_GEN_INT_FUNC_PTR finish_f);
	int ENGINE_set_ctrl_function(ENGINE *e,	ENGINE_CTRL_FUNC_PTR ctrl_f);
	int ENGINE_set_load_privkey_function(ENGINE *e,	ENGINE_LOAD_KEY_PTR loadpriv_f);
	int ENGINE_set_load_pubkey_function(ENGINE *e, ENGINE_LOAD_KEY_PTR loadpub_f);
	int ENGINE_set_ciphers(ENGINE *e, ENGINE_CIPHERS_PTR f);
	int ENGINE_set_digests(ENGINE *e, ENGINE_DIGESTS_PTR f);
	int ENGINE_set_flags(ENGINE *e,	int flags);
	int ENGINE_set_cmd_defns(ENGINE	*e, const ENGINE_CMD_DEFN *defns);

	const char *ENGINE_get_id(const	ENGINE *e);
	const char *ENGINE_get_name(const ENGINE *e);
	const RSA_METHOD *ENGINE_get_RSA(const ENGINE *e);
	const DSA_METHOD *ENGINE_get_DSA(const ENGINE *e);
	const DH_METHOD	*ENGINE_get_DH(const ENGINE *e);
	const RAND_METHOD *ENGINE_get_RAND(const ENGINE	*e);
	ENGINE_GEN_INT_FUNC_PTR	ENGINE_get_destroy_function(const ENGINE *e);
	ENGINE_GEN_INT_FUNC_PTR	ENGINE_get_init_function(const ENGINE *e);
	ENGINE_GEN_INT_FUNC_PTR	ENGINE_get_finish_function(const ENGINE	*e);
	ENGINE_CTRL_FUNC_PTR ENGINE_get_ctrl_function(const ENGINE *e);
	ENGINE_LOAD_KEY_PTR ENGINE_get_load_privkey_function(const ENGINE *e);
	ENGINE_LOAD_KEY_PTR ENGINE_get_load_pubkey_function(const ENGINE *e);
	ENGINE_CIPHERS_PTR ENGINE_get_ciphers(const ENGINE *e);
	ENGINE_DIGESTS_PTR ENGINE_get_digests(const ENGINE *e);
	const EVP_CIPHER *ENGINE_get_cipher(ENGINE *e, int nid);
	const EVP_MD *ENGINE_get_digest(ENGINE *e, int nid);
	int ENGINE_get_flags(const ENGINE *e);
	const ENGINE_CMD_DEFN *ENGINE_get_cmd_defns(const ENGINE *e);

	EVP_PKEY *ENGINE_load_private_key(ENGINE *e, const char	*key_id,
					  UI_METHOD *ui_method,	void *callback_data);
	EVP_PKEY *ENGINE_load_public_key(ENGINE	*e, const char *key_id,
					 UI_METHOD *ui_method, void *callback_data);

       Deprecated:

	#if OPENSSL_API_COMPAT < 0x10100000L
	void ENGINE_cleanup(void)
	#endif

DESCRIPTION
       These functions create, manipulate, and use cryptographic modules in
       the form	of ENGINE objects. These objects act as	containers for
       implementations of cryptographic	algorithms, and	support	a reference-
       counted mechanism to allow them to be dynamically loaded	in and out of
       the running application.

       The cryptographic functionality that can	be provided by an ENGINE
       implementation includes the following abstractions;

	RSA_METHOD - for providing alternative RSA implementations
	DSA_METHOD, DH_METHOD, RAND_METHOD, ECDH_METHOD, ECDSA_METHOD,
	      -	similarly for other OpenSSL APIs
	EVP_CIPHER - potentially multiple cipher algorithms (indexed by	'nid')
	EVP_DIGEST - potentially multiple hash algorithms (indexed by 'nid')
	key-loading - loading public and/or private EVP_PKEY keys

   Reference counting and handles
       Due to the modular nature of the	ENGINE API, pointers to	ENGINEs	need
       to be treated as	handles	- ie. not only as pointers, but	also as
       references to the underlying ENGINE object. Ie. one should obtain a new
       reference when making copies of an ENGINE pointer if the	copies will be
       used (and released) independently.

       ENGINE objects have two levels of reference-counting to match the way
       in which	the objects are	used. At the most basic	level, each ENGINE
       pointer is inherently a structural reference - a	structural reference
       is required to use the pointer value at all, as this kind of reference
       is a guarantee that the structure can not be deallocated	until the
       reference is released.

       However,	a structural reference provides	no guarantee that the ENGINE
       is initialised and able to use any of its cryptographic
       implementations.	Indeed it's quite possible that	most ENGINEs will not
       initialise at all in typical environments, as ENGINEs are typically
       used to support specialised hardware. To	use an ENGINE's	functionality,
       you need	a functional reference.	This kind of reference can be
       considered a specialised	form of	structural reference, because each
       functional reference implicitly contains	a structural reference as well
       - however to avoid difficult-to-find programming	bugs, it is
       recommended to treat the	two kinds of reference independently. If you
       have a functional reference to an ENGINE, you have a guarantee that the
       ENGINE has been initialised and is ready	to perform cryptographic
       operations, and will remain initialised until after you have released
       your reference.

       Structural references

       This basic type of reference is used for	instantiating new ENGINEs,
       iterating across	OpenSSL's internal linked-list of loaded ENGINEs,
       reading information about an ENGINE, etc. Essentially a structural
       reference is sufficient if you only need	to query or manipulate the
       data of an ENGINE implementation	rather than use	its functionality.

       The ENGINE_new()	function returns a structural reference	to a new
       (empty) ENGINE object. There are	other ENGINE API functions that	return
       structural references such as; ENGINE_by_id(), ENGINE_get_first(),
       ENGINE_get_last(), ENGINE_get_next(), ENGINE_get_prev().	All structural
       references should be released by	a corresponding	to call	to the
       ENGINE_free() function -	the ENGINE object itself will only actually be
       cleaned up and deallocated when the last	structural reference is
       released.

       It should also be noted that many ENGINE	API function calls that	accept
       a structural reference will internally obtain another reference -
       typically this happens whenever the supplied ENGINE will	be needed by
       OpenSSL after the function has returned.	Eg. the	function to add	a new
       ENGINE to OpenSSL's internal list is ENGINE_add() - if this function
       returns success,	then OpenSSL will have stored a	new structural
       reference internally so the caller is still responsible for freeing
       their own reference with	ENGINE_free() when they	are finished with it.
       In a similar way, some functions	will automatically release the
       structural reference passed to it if part of the	function's job is to
       do so. Eg. the ENGINE_get_next()	and ENGINE_get_prev() functions	are
       used for	iterating across the internal ENGINE list - they will return a
       new structural reference	to the next (or	previous) ENGINE in the	list
       or NULL if at the end (or beginning) of the list, but in	either case
       the structural reference	passed to the function is released on behalf
       of the caller.

       To clarify a particular function's handling of references, one should
       always consult that function's documentation "man" page,	or failing
       that the	openssl/engine.h header	file includes some hints.

       Functional references

       As mentioned, functional	references exist when the cryptographic
       functionality of	an ENGINE is required to be available. A functional
       reference can be	obtained in one	of two ways; from an existing
       structural reference to the required ENGINE, or by asking OpenSSL for
       the default operational ENGINE for a given cryptographic	purpose.

       To obtain a functional reference	from an	existing structural reference,
       call the	ENGINE_init() function.	This returns zero if the ENGINE	was
       not already operational and couldn't be successfully initialised	(eg.
       lack of system drivers, no special hardware attached, etc), otherwise
       it will return non-zero to indicate that	the ENGINE is now operational
       and will	have allocated a new functional	reference to the ENGINE. All
       functional references are released by calling ENGINE_finish() (which
       removes the implicit structural reference as well).

       The second way to get a functional reference is by asking OpenSSL for a
       default implementation for a given task,	eg. by
       ENGINE_get_default_RSA(), ENGINE_get_default_cipher_engine(), etc.
       These are discussed in the next section,	though they are	not usually
       required	by application programmers as they are used automatically when
       creating	and using the relevant algorithm-specific types	in OpenSSL,
       such as RSA, DSA, EVP_CIPHER_CTX, etc.

   Default implementations
       For each	supported abstraction, the ENGINE code maintains an internal
       table of	state to control which implementations are available for a
       given abstraction and which should be used by default. These
       implementations are registered in the tables and	indexed	by an 'nid'
       value, because abstractions like	EVP_CIPHER and EVP_DIGEST support many
       distinct	algorithms and modes, and ENGINEs can support arbitrarily many
       of them.	 In the	case of	other abstractions like	RSA, DSA, etc, there
       is only one "algorithm" so all implementations implicitly register
       using the same 'nid' index.

       When a default ENGINE is	requested for a	given
       abstraction/algorithm/mode, (eg.	 when calling RSA_new_method(NULL)), a
       "get_default" call will be made to the ENGINE subsystem to process the
       corresponding state table and return a functional reference to an
       initialised ENGINE whose	implementation should be used. If no ENGINE
       should (or can) be used,	it will	return NULL and	the caller will
       operate with a NULL ENGINE handle - this	usually	equates	to using the
       conventional software implementation. In	the latter case, OpenSSL will
       from then on behave the way it used to before the ENGINE	API existed.

       Each state table	has a flag to note whether it has processed this
       "get_default" query since the table was last modified, because to
       process this question it	must iterate across all	the registered ENGINEs
       in the table trying to initialise each of them in turn, in case one of
       them is operational. If it returns a functional reference to an ENGINE,
       it will also cache another reference to speed up	processing future
       queries (without	needing	to iterate across the table). Likewise,	it
       will cache a NULL response if no	ENGINE was available so	that future
       queries won't repeat the	same iteration unless the state	table changes.
       This behaviour can also be changed; if the ENGINE_TABLE_FLAG_NOINIT
       flag is set (using ENGINE_set_table_flags()), no	attempted
       initialisations will take place,	instead	the only way for the state
       table to	return a non-NULL ENGINE to the	"get_default" query will be if
       one is expressly	set in the table. Eg.  ENGINE_set_default_RSA()	does
       the same	job as ENGINE_register_RSA() except that it also sets the
       state table's cached response for the "get_default" query. In the case
       of abstractions like EVP_CIPHER,	where implementations are indexed by
       'nid', these flags and cached-responses are distinct for	each 'nid'
       value.

   Application requirements
       This section will explain the basic things an application programmer
       should support to make the most useful elements of the ENGINE
       functionality available to the user. The	first thing to consider	is
       whether the programmer wishes to	make alternative ENGINE	modules
       available to the	application and	user. OpenSSL maintains	an internal
       linked list of "visible"	ENGINEs	from which it has to operate - at
       start-up, this list is empty and	in fact	if an application does not
       call any	ENGINE API calls and it	uses static linking against openssl,
       then the	resulting application binary will not contain any alternative
       ENGINE code at all. So the first	consideration is whether any/all
       available ENGINE	implementations	should be made visible to OpenSSL -
       this is controlled by calling the various "load"	functions.

       The fact	that ENGINEs are made visible to OpenSSL (and thus are linked
       into the	program	and loaded into	memory at run-time) does not mean they
       are "registered"	or called into use by OpenSSL automatically - that
       behaviour is something for the application to control. Some
       applications will want to allow the user	to specify exactly which
       ENGINE they want	used if	any is to be used at all. Others may prefer to
       load all	support	and have OpenSSL automatically use at run-time any
       ENGINE that is able to successfully initialise -	ie. to assume that
       this corresponds	to acceleration	hardware attached to the machine or
       some such thing.	There are probably numerous other ways in which
       applications may	prefer to handle things, so we will simply illustrate
       the consequences	as they	apply to a couple of simple cases and leave
       developers to consider these and	the source code	to openssl's builtin
       utilities as guides.

       If no ENGINE API	functions are called within an application, then
       OpenSSL will not	allocate any internal resources.  Prior	to OpenSSL
       1.1.0, however, if any ENGINEs are loaded, even if not registered or
       used, it	was necessary to call ENGINE_cleanup() before the program
       exits.

       Using a specific	ENGINE implementation

       Here we'll assume an application	has been configured by its user	or
       admin to	want to	use the	"ACME" ENGINE if it is available in the
       version of OpenSSL the application was compiled with. If	it is
       available, it should be used by default for all RSA, DSA, and symmetric
       cipher operations, otherwise OpenSSL should use its builtin software as
       per usual. The following	code illustrates how to	approach this;

	ENGINE *e;
	const char *engine_id =	"ACME";
	ENGINE_load_builtin_engines();
	e = ENGINE_by_id(engine_id);
	if (!e)
	    /* the engine isn't	available */
	    return;
	if (!ENGINE_init(e)) {
	    /* the engine couldn't initialise, release 'e' */
	    ENGINE_free(e);
	    return;
	}
	if (!ENGINE_set_default_RSA(e))
	    /*
	     * This should only	happen when 'e'	can't initialise, but the previous
	     * statement suggests it did.
	     */
	    abort();
	ENGINE_set_default_DSA(e);
	ENGINE_set_default_ciphers(e);
	/* Release the functional reference from ENGINE_init() */
	ENGINE_finish(e);
	/* Release the structural reference from ENGINE_by_id()	*/
	ENGINE_free(e);

       Automatically using builtin ENGINE implementations

       Here we'll assume we want to load and register all ENGINE
       implementations bundled with OpenSSL, such that for any cryptographic
       algorithm required by OpenSSL - if there	is an ENGINE that implements
       it and can be initialised, it should be used. The following code
       illustrates how this can	work;

	/* Load	all bundled ENGINEs into memory	and make them visible */
	ENGINE_load_builtin_engines();
	/* Register all	of them	for every algorithm they collectively implement	*/
	ENGINE_register_all_complete();

       That's all that's required. Eg. the next	time OpenSSL tries to set up
       an RSA key, any bundled ENGINEs that implement RSA_METHOD will be
       passed to ENGINE_init() and if any of those succeed, that ENGINE	will
       be set as the default for RSA use from then on.

   Advanced configuration support
       There is	a mechanism supported by the ENGINE framework that allows each
       ENGINE implementation to	define an arbitrary set	of configuration
       "commands" and expose them to OpenSSL and any applications based	on
       OpenSSL.	This mechanism is entirely based on the	use of name-value
       pairs and assumes ASCII input (no unicode or UTF	for now!), so it is
       ideal if	applications want to provide a transparent way for users to
       provide arbitrary configuration "directives" directly to	such ENGINEs.
       It is also possible for the application to dynamically interrogate the
       loaded ENGINE implementations for the names, descriptions, and input
       flags of	their available	"control commands", providing a	more flexible
       configuration scheme. However, if the user is expected to know which
       ENGINE device he/she is using (in the case of specialised hardware,
       this goes without saying) then applications may not need	to concern
       themselves with discovering the supported control commands and simply
       prefer to pass settings into ENGINEs exactly as they are	provided by
       the user.

       Before illustrating how control commands	work, it is worth mentioning
       what they are typically used for. Broadly speaking there	are two	uses
       for control commands; the first is to provide the necessary details to
       the implementation (which may know nothing at all specific to the host
       system) so that it can be initialised for use. This could include the
       path to any driver or config files it needs to load, required network
       addresses, smart-card identifiers, passwords to initialise protected
       devices,	logging	information, etc etc. This class of commands typically
       needs to	be passed to an	ENGINE before attempting to initialise it, ie.
       before calling ENGINE_init(). The other class of	commands consist of
       settings	or operations that tweak certain behaviour or cause certain
       operations to take place, and these commands may	work either before or
       after ENGINE_init(), or in some cases both. ENGINE implementations
       should provide indications of this in the descriptions attached to
       builtin control commands	and/or in external product documentation.

       Issuing control commands	to an ENGINE

       Let's illustrate	by example; a function for which the caller supplies
       the name	of the ENGINE it wishes	to use,	a table	of string-pairs	for
       use before initialisation, and another table for	use after
       initialisation. Note that the string-pairs used for control commands
       consist of a command "name" followed by the command "parameter" - the
       parameter could be NULL in some cases but the name can not. This
       function	should initialise the ENGINE (issuing the "pre"	commands
       beforehand and the "post" commands afterwards) and set it as the
       default for everything except RAND and then return a boolean success or
       failure.

	int generic_load_engine_fn(const char *engine_id,
				   const char **pre_cmds, int pre_num,
				   const char **post_cmds, int post_num)
	{
	    ENGINE *e =	ENGINE_by_id(engine_id);
	    if (!e) return 0;
	    while (pre_num--) {
		if (!ENGINE_ctrl_cmd_string(e, pre_cmds[0], pre_cmds[1], 0)) {
		    fprintf(stderr, "Failed command (%s	- %s:%s)\n", engine_id,
			    pre_cmds[0], pre_cmds[1] ? pre_cmds[1] : "(NULL)");
		    ENGINE_free(e);
		    return 0;
		}
		pre_cmds += 2;
	    }
	    if (!ENGINE_init(e)) {
		fprintf(stderr,	"Failed	initialisation\n");
		ENGINE_free(e);
		return 0;
	    }
	    /*
	     * ENGINE_init() returned a	functional reference, so free the structural
	     * reference from ENGINE_by_id().
	     */
	    ENGINE_free(e);
	    while (post_num--) {
		if (!ENGINE_ctrl_cmd_string(e, post_cmds[0], post_cmds[1], 0)) {
		    fprintf(stderr, "Failed command (%s	- %s:%s)\n", engine_id,
			    post_cmds[0], post_cmds[1] ? post_cmds[1] :	"(NULL)");
		    ENGINE_finish(e);
		    return 0;
		}
		post_cmds += 2;
	    }
	    ENGINE_set_default(e, ENGINE_METHOD_ALL & ~ENGINE_METHOD_RAND);
	    /* Success */
	    return 1;
	}

       Note that ENGINE_ctrl_cmd_string() accepts a boolean argument that can
       relax the semantics of the function - if	set non-zero it	will only
       return failure if the ENGINE supported the given	command	name but
       failed while executing it, if the ENGINE	doesn't	support	the command
       name it will simply return success without doing	anything. In this case
       we assume the user is only supplying commands specific to the given
       ENGINE so we set	this to	FALSE.

       Discovering supported control commands

       It is possible to discover at run-time the names, numerical-ids,
       descriptions and	input parameters of the	control	commands supported by
       an ENGINE using a structural reference. Note that some control commands
       are defined by OpenSSL itself and it will intercept and handle these
       control commands	on behalf of the ENGINE, ie. the ENGINE's ctrl()
       handler is not used for the control command.  openssl/engine.h defines
       an index, ENGINE_CMD_BASE, that all control commands implemented	by
       ENGINEs should be numbered from.	Any command value lower	than this
       symbol is considered a "generic"	command	is handled directly by the
       OpenSSL core routines.

       It is using these "core"	control	commands that one can discover the
       control commands	implemented by a given ENGINE, specifically the
       commands:

	ENGINE_HAS_CTRL_FUNCTION
	ENGINE_CTRL_GET_FIRST_CMD_TYPE
	ENGINE_CTRL_GET_NEXT_CMD_TYPE
	ENGINE_CTRL_GET_CMD_FROM_NAME
	ENGINE_CTRL_GET_NAME_LEN_FROM_CMD
	ENGINE_CTRL_GET_NAME_FROM_CMD
	ENGINE_CTRL_GET_DESC_LEN_FROM_CMD
	ENGINE_CTRL_GET_DESC_FROM_CMD
	ENGINE_CTRL_GET_CMD_FLAGS

       Whilst these commands are automatically processed by the	OpenSSL
       framework code, they use	various	properties exposed by each ENGINE to
       process these queries. An ENGINE	has 3 properties it exposes that can
       affect how this behaves;	it can supply a	ctrl() handler,	it can specify
       ENGINE_FLAGS_MANUAL_CMD_CTRL in the ENGINE's flags, and it can expose
       an array	of control command descriptions.  If an	ENGINE specifies the
       ENGINE_FLAGS_MANUAL_CMD_CTRL flag, then it will simply pass all these
       "core" control commands directly	to the ENGINE's	ctrl() handler (and
       thus, it	must have supplied one), so it is up to	the ENGINE to reply to
       these "discovery" commands itself. If that flag is not set, then	the
       OpenSSL framework code will work	with the following rules:

	if no ctrl() handler supplied;
	    ENGINE_HAS_CTRL_FUNCTION returns FALSE (zero),
	    all	other commands fail.
	if a ctrl() handler was	supplied but no	array of control commands;
	    ENGINE_HAS_CTRL_FUNCTION returns TRUE,
	    all	other commands fail.
	if a ctrl() handler and	array of control commands was supplied;
	    ENGINE_HAS_CTRL_FUNCTION returns TRUE,
	    all	other commands proceed processing ...

       If the ENGINE's array of	control	commands is empty then all other
       commands	will fail, otherwise; ENGINE_CTRL_GET_FIRST_CMD_TYPE returns
       the identifier of the first command supported by	the ENGINE,
       ENGINE_GET_NEXT_CMD_TYPE	takes the identifier of	a command supported by
       the ENGINE and returns the next command identifier or fails if there
       are no more, ENGINE_CMD_FROM_NAME takes a string	name for a command and
       returns the corresponding identifier or fails if	no such	command	name
       exists, and the remaining commands take a command identifier and	return
       properties of the corresponding commands. All except
       ENGINE_CTRL_GET_FLAGS return the	string length of a command name	or
       description, or populate	a supplied character buffer with a copy	of the
       command name or description. ENGINE_CTRL_GET_FLAGS returns a bitwise-
       OR'd mask of the	following possible values:

	ENGINE_CMD_FLAG_NUMERIC
	ENGINE_CMD_FLAG_STRING
	ENGINE_CMD_FLAG_NO_INPUT
	ENGINE_CMD_FLAG_INTERNAL

       If the ENGINE_CMD_FLAG_INTERNAL flag is set, then any other flags are
       purely informational to the caller - this flag will prevent the command
       being usable for	any higher-level ENGINE	functions such as
       ENGINE_ctrl_cmd_string().  "INTERNAL" commands are not intended to be
       exposed to text-based configuration by applications, administrations,
       users, etc. These can support arbitrary operations via ENGINE_ctrl(),
       including passing to and/or from	the control commands data of any
       arbitrary type. These commands are supported in the discovery
       mechanisms simply to allow applications to determine if an ENGINE
       supports	certain	specific commands it might want	to use (eg.
       application "foo" might query various ENGINEs to	see if they implement
       "FOO_GET_VENDOR_LOGO_GIF" - and ENGINE could therefore decide whether
       or not to support this "foo"-specific extension).

ENVIRONMENT
       OPENSSL_ENGINES
	   The path to the engines directory.  Ignored in set-user-ID and set-
	   group-ID programs.

RETURN VALUES
       ENGINE_get_first(), ENGINE_get_last(), ENGINE_get_next()	and
       ENGINE_get_prev() return	a valid	ENGINE structure or NULL if an error
       occurred.

       ENGINE_add() and	ENGINE_remove()	return 1 on success or 0 on error.

       ENGINE_by_id() returns a	valid ENGINE structure or NULL if an error
       occurred.

       ENGINE_init() and ENGINE_finish() return	1 on success or	0 on error.

       All ENGINE_get_default_TYPE() functions,	ENGINE_get_cipher_engine() and
       ENGINE_get_digest_engine() return a valid ENGINE	structure on success
       or NULL if an error occurred.

       All ENGINE_set_default_TYPE() functions return 1	on success or 0	on
       error.

       ENGINE_set_default() returns 1 on success or 0 on error.

       ENGINE_get_table_flags()	returns	an unsigned integer value representing
       the global table	flags which are	used to	control	the registration
       behaviour of ENGINE implementations.

       All ENGINE_register_TYPE() functions return 1 on	success	or 0 on	error.

       ENGINE_register_complete() and ENGINE_register_all_complete() return 1
       on success or 0 on error.

       ENGINE_ctrl() returns a positive	value on success or others on error.

       ENGINE_cmd_is_executable() returns 1 if cmd is executable or 0
       otherwise.

       ENGINE_ctrl_cmd() and ENGINE_ctrl_cmd_string() return 1 on success or 0
       on error.

       ENGINE_new() returns a valid ENGINE structure on	success	or NULL	if an
       error occurred.

       ENGINE_free() returns 1 on success or 0 on error.

       ENGINE_up_ref() returns 1 on success or 0 on error.

       ENGINE_set_id() and ENGINE_set_name() return 1 on success or 0 on
       error.

       All other ENGINE_set_* functions	return 1 on success or 0 on error.

       ENGINE_get_id() and ENGINE_get_name() return a string representing the
       identifier and the name of the ENGINE e respectively.

       ENGINE_get_RSA(), ENGINE_get_DSA(), ENGINE_get_DH() and
       ENGINE_get_RAND() return	corresponding method structures	for each
       algorithms.

       ENGINE_get_destroy_function(), ENGINE_get_init_function(),
       ENGINE_get_finish_function(), ENGINE_get_ctrl_function(),
       ENGINE_get_load_privkey_function(), ENGINE_get_load_pubkey_function(),
       ENGINE_get_ciphers() and	ENGINE_get_digests() return corresponding
       function	pointers of the	callbacks.

       ENGINE_get_cipher() returns a valid EVP_CIPHER structure	on success or
       NULL if an error	occurred.

       ENGINE_get_digest() returns a valid EVP_MD structure on success or NULL
       if an error occurred.

       ENGINE_get_flags() returns an integer representing the ENGINE flags
       which are used to control various behaviours of an ENGINE.

       ENGINE_get_cmd_defns() returns an ENGINE_CMD_DEFN structure or NULL if
       it's not	set.

       ENGINE_load_private_key() and ENGINE_load_public_key() return a valid
       EVP_PKEY	structure on success or	NULL if	an error occurred.

SEE ALSO
       OPENSSL_init_crypto(3), RSA_new_method(3), DSA_new(3), DH_new(3),
       RAND_bytes(3), config(5)

HISTORY
       ENGINE_cleanup()	was deprecated in OpenSSL 1.1.0	by the automatic
       cleanup done by OPENSSL_cleanup() and should not	be used.

COPYRIGHT
       Copyright 2002-2018 The OpenSSL Project Authors.	All Rights Reserved.

       Licensed	under the OpenSSL license (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>.

1.1.1d				  2019-09-10			 ENGINE_ADD(3)

NAME | SYNOPSIS | DESCRIPTION | ENVIRONMENT | RETURN VALUES | SEE ALSO | HISTORY | COPYRIGHT

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