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engine(3)				     OpenSSL					engine(3)

       engine - ENGINE cryptographic module support

	#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_openssl(void);
	void ENGINE_load_dynamic(void);
	void ENGINE_load_cswift(void);
	void ENGINE_load_chil(void);
	void ENGINE_load_atalla(void);
	void ENGINE_load_nuron(void);
	void ENGINE_load_ubsec(void);
	void ENGINE_load_aep(void);
	void ENGINE_load_sureware(void);
	void ENGINE_load_4758cca(void);
	void ENGINE_load_openbsd_dev_crypto(void);
	void ENGINE_load_builtin_engines(void);

	void ENGINE_cleanup(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)());
	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)(), int cmd_optional);
	int ENGINE_ctrl_cmd_string(ENGINE *e, const char *cmd_name, const char *arg,
			int cmd_optional);

	int ENGINE_set_ex_data(ENGINE *e, int idx, void *arg);
	void *ENGINE_get_ex_data(const ENGINE *e, int idx);

	int ENGINE_get_ex_new_index(long argl, void *argp, CRYPTO_EX_new *new_func,
		CRYPTO_EX_dup *dup_func, CRYPTO_EX_free *free_func);

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

	void ENGINE_add_conf_module(void);

       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
	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. you should obtain a new reference when making copies of an ENGINE pointer if
       the copies will be used (and released) independantly.

       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 refer-
       ence - you need a structural reference simply to refer to the pointer value at all, as
       this kind of reference is your guarantee that the structure can not be deallocated until
       you release your reference.

       However, a structural reference provides no guarantee that the ENGINE has been initiliased
       to be usable to perform any of its cryptographic implementations - and indeed it's quite
       possible that most ENGINEs will not initialised at all on standard setups, 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 independantly. If you have a functional reference to
       an ENGINE, you have a guarantee that the ENGINE has been initialised ready to perform
       cryptographic operations and will not be uninitialised or cleaned up until after you have
       released your reference.

       We will discuss the two kinds of reference separately, including how to tell which one you
       are dealing with at any given point in time (after all they are both simply (ENGINE *)
       pointers, the difference is in the way they are used).

       Structural references

       This basic type of reference is typically used for creating new ENGINEs dynamically, iter-
       ating 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.
       Other than that, structural references come from return values to various ENGINE API func-
       tions 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 ref-
       erence will internally obtain another reference - typically this happens whenever the sup-
       plied 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 fin-
       ished 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 inter-
       nal 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 oper-
       ational and will have allocated a new functional reference to the ENGINE. In this case,
       the supplied ENGINE pointer is, from the point of the view of the caller, both a struc-
       tural reference and a functional reference - so if the caller intends to use it as a func-
       tional reference it should free the structural reference with ENGINE_free() first. If the
       caller wishes to use it only as a structural reference (eg. if the ENGINE_init() call was
       simply to test if the ENGINE seems available/online), then it should free the functional
       reference; all functional references are released by the ENGINE_finish() function.

       The second way to get a functional reference is by asking OpenSSL for a default implemen-
       tation 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 separated-out by an
       'nid' index, because abstractions like EVP_CIPHER and EVP_DIGEST support many distinct
       algorithms and modes - ENGINEs will support different numbers and combinations of these.
       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. ENGINEs can be registered
       into these tables to make themselves available for use automatically by the various
       abstractions, eg. RSA. For illustrative purposes, we continue with the RSA example, though
       all comments apply similarly to the other abstractions (they each get their own table and
       linkage to the corresponding section of openssl code).

       When a new RSA key is being created, ie. in RSA_new_method(), a "get_default" call will be
       made to the ENGINE subsystem to process the RSA state table and return a functional refer-
       ence to an initialised ENGINE whose RSA_METHOD should be used. If no ENGINE should (or
       can) be used, it will return NULL and the RSA key will operate with a NULL ENGINE handle
       by using the conventional RSA implementation in OpenSSL (and will from then on behave the
       way it used to before the ENGINE API existed - for details see RSA_new_method(3)).

       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 avail-
       able 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.

       It is worth illustrating the difference between "registration" of ENGINEs into these per-
       algorithm state tables and using the alternative "set_default" functions. The latter han-
       dles both "registration" and also setting the cached "default" ENGINE in each relevant
       state table - so registered ENGINEs will only have a chance to be initialised for use as a
       default if a default ENGINE wasn't already set for the same state table.  Eg. if ENGINE X
       supports cipher nids {A,B} and RSA, ENGINE Y supports ciphers {A} and DSA, and the follow-
       ing code is executed;

	e1 = ENGINE_get_default_RSA();
	e2 = ENGINE_get_cipher_engine(A);
	e3 = ENGINE_get_cipher_engine(B);
	e4 = ENGINE_get_default_DSA();
	e5 = ENGINE_get_cipher_engine(C);

       The results would be as follows;

	assert(e1 == X);
	assert(e2 == Y);
	assert(e3 == X);
	assert(e4 == Y);
	assert(e5 == NULL);

       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 "visi-
       ble" 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 implementa-
       tions should be made visible to OpenSSL - this is controlled by calling the various "load"
       functions, eg.

	/* Make the "dynamic" ENGINE available */
	void ENGINE_load_dynamic(void);
	/* Make the CryptoSwift hardware acceleration support available */
	void ENGINE_load_cswift(void);
	/* Make support for nCipher's "CHIL" hardware available */
	void ENGINE_load_chil(void);
	/* Make ALL ENGINE implementations bundled with OpenSSL available */
	void ENGINE_load_builtin_engines(void);

       Having called any of these functions, ENGINE objects would have been dynamically allocated
       and populated with these implementations and linked into OpenSSL's internal linked list.
       At this point it is important to mention an important API function;

	void ENGINE_cleanup(void);

       If no ENGINE API functions are called at all in an application, then there are no inherent
       memory leaks to worry about from the ENGINE functionality, however if any ENGINEs are
       "load"ed, even if they are never registered or used, it is necessary to use the
       ENGINE_cleanup() function to correspondingly cleanup before program exit, if the caller
       wishes to avoid memory leaks. This mechanism uses an internal callback registration table
       so that any ENGINE API functionality that knows it requires cleanup can register its
       cleanup details to be called during ENGINE_cleanup(). This approach allows
       ENGINE_cleanup() to clean up after any ENGINE functionality at all that your program uses,
       yet doesn't automatically create linker dependencies to all possible ENGINE functionality
       - only the cleanup callbacks required by the functionality you do use will be required by
       the linker.

       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 have control
       over. 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.

       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 com-
       piled with. If it is available, it should be used by default for all RSA, DSA, and symmet-
       ric cipher operation, otherwise OpenSSL should use its builtin software as per usual. The
       following code illustrates how to approach this;

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

       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 initialise, it should be used. The following code
       illustrates how this can work;

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

       That's all that's required. Eg. the next time OpenSSL tries to set up an RSA key, any bun-
       dled 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 use with RSA from then on.

       Advanced configuration support

       There is a mechanism supported by the ENGINE framework that allows each ENGINE implementa-
       tion 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 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 configura-
       tion "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
       allow settings to passed into ENGINEs exactly as they are provided by the user.

       Before illustrating how control commands work, it is worth mentioning what they are typi-
       cally 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 spe-
       cific 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 password-protected devices, logging information,
       etc etc. This class of commands typically needs to be passed to an ENGINE before attempt-
       ing to initialise it, ie. before calling ENGINE_init(). The other class of commands con-
       sist 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 same
       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)");
		    return 0;
		pre_cmds += 2;
	    if(!ENGINE_init(e)) {
		fprintf(stderr, "Failed initialisation\n");
		return 0;
	    /* ENGINE_init() returned a functional reference, so free the structural
	     * reference from ENGINE_by_id(). */
	    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)");
		    return 0;
		post_cmds += 2;
	    /* 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 com-
       mand 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 from a structural reference to any ENGINE. It
       is first important to 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 a symbol,
       ENGINE_CMD_BASE, that all control commands implemented by ENGINEs 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 the control commands
       implemented by a given ENGINE, specifically the commands;

	#define ENGINE_HAS_CTRL_FUNCTION	       10
	#define ENGINE_CTRL_GET_NEXT_CMD_TYPE	       12
	#define ENGINE_CTRL_GET_CMD_FROM_NAME	       13
	#define ENGINE_CTRL_GET_NAME_FROM_CMD	       15
	#define ENGINE_CTRL_GET_DESC_FROM_CMD	       17
	#define ENGINE_CTRL_GET_CMD_FLAGS	       18

       Whilst these commands are automatically processed by the OpenSSL framework code, they use
       various properties exposed by each ENGINE by which to process these queries. An ENGINE has
       3 properties it exposes that can affect this behaviour; 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;
	    all other commands fail.
	if a ctrl() handler was supplied but no array of control commands;
	    all other commands fail.
	if a ctrl() handler and array of control commands was supplied;
	    all other commands proceed processing ...

       If the ENGINE's array of control commands is empty then all other commands will fail, oth-
       erwise; ENGINE_CTRL_GET_FIRST_CMD_TYPE returns the identifier of the first command sup-
       ported 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 iden-
       tifier 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 popu-
       late 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;

	#define ENGINE_CMD_FLAG_NUMERIC 	       (unsigned int)0x0001
	#define ENGINE_CMD_FLAG_STRING		       (unsigned int)0x0002
	#define ENGINE_CMD_FLAG_NO_INPUT	       (unsigned int)0x0004
	#define ENGINE_CMD_FLAG_INTERNAL	       (unsigned int)0x0008

       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 dis-
       covery mechanisms simply to allow applications determinie 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).

       Future developments

       The ENGINE API and internal architecture is currently being reviewed. Slated for possible
       release in 0.9.8 is support for transparent loading of "dynamic" ENGINEs (built as self-
       contained shared-libraries). This would allow ENGINE implementations to be provided inde-
       pendantly of OpenSSL libraries and/or OpenSSL-based applications, and would also remove
       any requirement for applications to explicitly use the "dynamic" ENGINE to bind to shared-
       library implementations.

       rsa(3), dsa(3), dh(3), rand(3), RSA_new_method(3)

0.9.7a					    2002-12-15					engine(3)
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