1engine(3)                           OpenSSL                          engine(3)
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NAME

6       engine - ENGINE cryptographic module support
7

SYNOPSIS

9        #include <openssl/engine.h>
10
11        ENGINE *ENGINE_get_first(void);
12        ENGINE *ENGINE_get_last(void);
13        ENGINE *ENGINE_get_next(ENGINE *e);
14        ENGINE *ENGINE_get_prev(ENGINE *e);
15
16        int ENGINE_add(ENGINE *e);
17        int ENGINE_remove(ENGINE *e);
18
19        ENGINE *ENGINE_by_id(const char *id);
20
21        int ENGINE_init(ENGINE *e);
22        int ENGINE_finish(ENGINE *e);
23
24        void ENGINE_load_openssl(void);
25        void ENGINE_load_dynamic(void);
26        #ifndef OPENSSL_NO_STATIC_ENGINE
27        void ENGINE_load_4758cca(void);
28        void ENGINE_load_aep(void);
29        void ENGINE_load_atalla(void);
30        void ENGINE_load_chil(void);
31        void ENGINE_load_cswift(void);
32        void ENGINE_load_gmp(void);
33        void ENGINE_load_nuron(void);
34        void ENGINE_load_sureware(void);
35        void ENGINE_load_ubsec(void);
36        #endif
37        void ENGINE_load_cryptodev(void);
38        void ENGINE_load_builtin_engines(void);
39
40        void ENGINE_cleanup(void);
41
42        ENGINE *ENGINE_get_default_RSA(void);
43        ENGINE *ENGINE_get_default_DSA(void);
44        ENGINE *ENGINE_get_default_ECDH(void);
45        ENGINE *ENGINE_get_default_ECDSA(void);
46        ENGINE *ENGINE_get_default_DH(void);
47        ENGINE *ENGINE_get_default_RAND(void);
48        ENGINE *ENGINE_get_cipher_engine(int nid);
49        ENGINE *ENGINE_get_digest_engine(int nid);
50
51        int ENGINE_set_default_RSA(ENGINE *e);
52        int ENGINE_set_default_DSA(ENGINE *e);
53        int ENGINE_set_default_ECDH(ENGINE *e);
54        int ENGINE_set_default_ECDSA(ENGINE *e);
55        int ENGINE_set_default_DH(ENGINE *e);
56        int ENGINE_set_default_RAND(ENGINE *e);
57        int ENGINE_set_default_ciphers(ENGINE *e);
58        int ENGINE_set_default_digests(ENGINE *e);
59        int ENGINE_set_default_string(ENGINE *e, const char *list);
60
61        int ENGINE_set_default(ENGINE *e, unsigned int flags);
62
63        unsigned int ENGINE_get_table_flags(void);
64        void ENGINE_set_table_flags(unsigned int flags);
65
66        int ENGINE_register_RSA(ENGINE *e);
67        void ENGINE_unregister_RSA(ENGINE *e);
68        void ENGINE_register_all_RSA(void);
69        int ENGINE_register_DSA(ENGINE *e);
70        void ENGINE_unregister_DSA(ENGINE *e);
71        void ENGINE_register_all_DSA(void);
72        int ENGINE_register_ECDH(ENGINE *e);
73        void ENGINE_unregister_ECDH(ENGINE *e);
74        void ENGINE_register_all_ECDH(void);
75        int ENGINE_register_ECDSA(ENGINE *e);
76        void ENGINE_unregister_ECDSA(ENGINE *e);
77        void ENGINE_register_all_ECDSA(void);
78        int ENGINE_register_DH(ENGINE *e);
79        void ENGINE_unregister_DH(ENGINE *e);
80        void ENGINE_register_all_DH(void);
81        int ENGINE_register_RAND(ENGINE *e);
82        void ENGINE_unregister_RAND(ENGINE *e);
83        void ENGINE_register_all_RAND(void);
84        int ENGINE_register_STORE(ENGINE *e);
85        void ENGINE_unregister_STORE(ENGINE *e);
86        void ENGINE_register_all_STORE(void);
87        int ENGINE_register_ciphers(ENGINE *e);
88        void ENGINE_unregister_ciphers(ENGINE *e);
89        void ENGINE_register_all_ciphers(void);
90        int ENGINE_register_digests(ENGINE *e);
91        void ENGINE_unregister_digests(ENGINE *e);
92        void ENGINE_register_all_digests(void);
93        int ENGINE_register_complete(ENGINE *e);
94        int ENGINE_register_all_complete(void);
95
96        int ENGINE_ctrl(ENGINE *e, int cmd, long i, void *p, void (*f)(void));
97        int ENGINE_cmd_is_executable(ENGINE *e, int cmd);
98        int ENGINE_ctrl_cmd(ENGINE *e, const char *cmd_name,
99                long i, void *p, void (*f)(void), int cmd_optional);
100        int ENGINE_ctrl_cmd_string(ENGINE *e, const char *cmd_name, const char *arg,
101                int cmd_optional);
102
103        int ENGINE_set_ex_data(ENGINE *e, int idx, void *arg);
104        void *ENGINE_get_ex_data(const ENGINE *e, int idx);
105
106        int ENGINE_get_ex_new_index(long argl, void *argp, CRYPTO_EX_new *new_func,
107                CRYPTO_EX_dup *dup_func, CRYPTO_EX_free *free_func);
108
109        ENGINE *ENGINE_new(void);
110        int ENGINE_free(ENGINE *e);
111        int ENGINE_up_ref(ENGINE *e);
112
113        int ENGINE_set_id(ENGINE *e, const char *id);
114        int ENGINE_set_name(ENGINE *e, const char *name);
115        int ENGINE_set_RSA(ENGINE *e, const RSA_METHOD *rsa_meth);
116        int ENGINE_set_DSA(ENGINE *e, const DSA_METHOD *dsa_meth);
117        int ENGINE_set_ECDH(ENGINE *e, const ECDH_METHOD *dh_meth);
118        int ENGINE_set_ECDSA(ENGINE *e, const ECDSA_METHOD *dh_meth);
119        int ENGINE_set_DH(ENGINE *e, const DH_METHOD *dh_meth);
120        int ENGINE_set_RAND(ENGINE *e, const RAND_METHOD *rand_meth);
121        int ENGINE_set_STORE(ENGINE *e, const STORE_METHOD *rand_meth);
122        int ENGINE_set_destroy_function(ENGINE *e, ENGINE_GEN_INT_FUNC_PTR destroy_f);
123        int ENGINE_set_init_function(ENGINE *e, ENGINE_GEN_INT_FUNC_PTR init_f);
124        int ENGINE_set_finish_function(ENGINE *e, ENGINE_GEN_INT_FUNC_PTR finish_f);
125        int ENGINE_set_ctrl_function(ENGINE *e, ENGINE_CTRL_FUNC_PTR ctrl_f);
126        int ENGINE_set_load_privkey_function(ENGINE *e, ENGINE_LOAD_KEY_PTR loadpriv_f);
127        int ENGINE_set_load_pubkey_function(ENGINE *e, ENGINE_LOAD_KEY_PTR loadpub_f);
128        int ENGINE_set_ciphers(ENGINE *e, ENGINE_CIPHERS_PTR f);
129        int ENGINE_set_digests(ENGINE *e, ENGINE_DIGESTS_PTR f);
130        int ENGINE_set_flags(ENGINE *e, int flags);
131        int ENGINE_set_cmd_defns(ENGINE *e, const ENGINE_CMD_DEFN *defns);
132
133        const char *ENGINE_get_id(const ENGINE *e);
134        const char *ENGINE_get_name(const ENGINE *e);
135        const RSA_METHOD *ENGINE_get_RSA(const ENGINE *e);
136        const DSA_METHOD *ENGINE_get_DSA(const ENGINE *e);
137        const ECDH_METHOD *ENGINE_get_ECDH(const ENGINE *e);
138        const ECDSA_METHOD *ENGINE_get_ECDSA(const ENGINE *e);
139        const DH_METHOD *ENGINE_get_DH(const ENGINE *e);
140        const RAND_METHOD *ENGINE_get_RAND(const ENGINE *e);
141        const STORE_METHOD *ENGINE_get_STORE(const ENGINE *e);
142        ENGINE_GEN_INT_FUNC_PTR ENGINE_get_destroy_function(const ENGINE *e);
143        ENGINE_GEN_INT_FUNC_PTR ENGINE_get_init_function(const ENGINE *e);
144        ENGINE_GEN_INT_FUNC_PTR ENGINE_get_finish_function(const ENGINE *e);
145        ENGINE_CTRL_FUNC_PTR ENGINE_get_ctrl_function(const ENGINE *e);
146        ENGINE_LOAD_KEY_PTR ENGINE_get_load_privkey_function(const ENGINE *e);
147        ENGINE_LOAD_KEY_PTR ENGINE_get_load_pubkey_function(const ENGINE *e);
148        ENGINE_CIPHERS_PTR ENGINE_get_ciphers(const ENGINE *e);
149        ENGINE_DIGESTS_PTR ENGINE_get_digests(const ENGINE *e);
150        const EVP_CIPHER *ENGINE_get_cipher(ENGINE *e, int nid);
151        const EVP_MD *ENGINE_get_digest(ENGINE *e, int nid);
152        int ENGINE_get_flags(const ENGINE *e);
153        const ENGINE_CMD_DEFN *ENGINE_get_cmd_defns(const ENGINE *e);
154
155        EVP_PKEY *ENGINE_load_private_key(ENGINE *e, const char *key_id,
156            UI_METHOD *ui_method, void *callback_data);
157        EVP_PKEY *ENGINE_load_public_key(ENGINE *e, const char *key_id,
158            UI_METHOD *ui_method, void *callback_data);
159
160        void ENGINE_add_conf_module(void);
161

DESCRIPTION

163       These functions create, manipulate, and use cryptographic modules in
164       the form of ENGINE objects. These objects act as containers for
165       implementations of cryptographic algorithms, and support a reference-
166       counted mechanism to allow them to be dynamically loaded in and out of
167       the running application.
168
169       The cryptographic functionality that can be provided by an ENGINE
170       implementation includes the following abstractions;
171
172        RSA_METHOD - for providing alternative RSA implementations
173        DSA_METHOD, DH_METHOD, RAND_METHOD, ECDH_METHOD, ECDSA_METHOD,
174              STORE_METHOD - similarly for other OpenSSL APIs
175        EVP_CIPHER - potentially multiple cipher algorithms (indexed by 'nid')
176        EVP_DIGEST - potentially multiple hash algorithms (indexed by 'nid')
177        key-loading - loading public and/or private EVP_PKEY keys
178
179   Reference counting and handles
180       Due to the modular nature of the ENGINE API, pointers to ENGINEs need
181       to be treated as handles - ie. not only as pointers, but also as
182       references to the underlying ENGINE object. Ie. one should obtain a new
183       reference when making copies of an ENGINE pointer if the copies will be
184       used (and released) independently.
185
186       ENGINE objects have two levels of reference-counting to match the way
187       in which the objects are used. At the most basic level, each ENGINE
188       pointer is inherently a structural reference - a structural reference
189       is required to use the pointer value at all, as this kind of reference
190       is a guarantee that the structure can not be deallocated until the
191       reference is released.
192
193       However, a structural reference provides no guarantee that the ENGINE
194       is initialised and able to use any of its cryptographic
195       implementations. Indeed it's quite possible that most ENGINEs will not
196       initialise at all in typical environments, as ENGINEs are typically
197       used to support specialised hardware. To use an ENGINE's functionality,
198       you need a functional reference. This kind of reference can be
199       considered a specialised form of structural reference, because each
200       functional reference implicitly contains a structural reference as well
201       - however to avoid difficult-to-find programming bugs, it is
202       recommended to treat the two kinds of reference independently. If you
203       have a functional reference to an ENGINE, you have a guarantee that the
204       ENGINE has been initialised and is ready to perform cryptographic
205       operations, and will remain initialised until after you have released
206       your reference.
207
208       Structural references
209
210       This basic type of reference is used for instantiating new ENGINEs,
211       iterating across OpenSSL's internal linked-list of loaded ENGINEs,
212       reading information about an ENGINE, etc. Essentially a structural
213       reference is sufficient if you only need to query or manipulate the
214       data of an ENGINE implementation rather than use its functionality.
215
216       The ENGINE_new() function returns a structural reference to a new
217       (empty) ENGINE object. There are other ENGINE API functions that return
218       structural references such as; ENGINE_by_id(), ENGINE_get_first(),
219       ENGINE_get_last(), ENGINE_get_next(), ENGINE_get_prev(). All structural
220       references should be released by a corresponding to call to the
221       ENGINE_free() function - the ENGINE object itself will only actually be
222       cleaned up and deallocated when the last structural reference is
223       released.
224
225       It should also be noted that many ENGINE API function calls that accept
226       a structural reference will internally obtain another reference -
227       typically this happens whenever the supplied ENGINE will be needed by
228       OpenSSL after the function has returned. Eg. the function to add a new
229       ENGINE to OpenSSL's internal list is ENGINE_add() - if this function
230       returns success, then OpenSSL will have stored a new structural
231       reference internally so the caller is still responsible for freeing
232       their own reference with ENGINE_free() when they are finished with it.
233       In a similar way, some functions will automatically release the
234       structural reference passed to it if part of the function's job is to
235       do so. Eg. the ENGINE_get_next() and ENGINE_get_prev() functions are
236       used for iterating across the internal ENGINE list - they will return a
237       new structural reference to the next (or previous) ENGINE in the list
238       or NULL if at the end (or beginning) of the list, but in either case
239       the structural reference passed to the function is released on behalf
240       of the caller.
241
242       To clarify a particular function's handling of references, one should
243       always consult that function's documentation "man" page, or failing
244       that the openssl/engine.h header file includes some hints.
245
246       Functional references
247
248       As mentioned, functional references exist when the cryptographic
249       functionality of an ENGINE is required to be available. A functional
250       reference can be obtained in one of two ways; from an existing
251       structural reference to the required ENGINE, or by asking OpenSSL for
252       the default operational ENGINE for a given cryptographic purpose.
253
254       To obtain a functional reference from an existing structural reference,
255       call the ENGINE_init() function. This returns zero if the ENGINE was
256       not already operational and couldn't be successfully initialised (eg.
257       lack of system drivers, no special hardware attached, etc), otherwise
258       it will return non-zero to indicate that the ENGINE is now operational
259       and will have allocated a new functional reference to the ENGINE. All
260       functional references are released by calling ENGINE_finish() (which
261       removes the implicit structural reference as well).
262
263       The second way to get a functional reference is by asking OpenSSL for a
264       default implementation for a given task, eg. by
265       ENGINE_get_default_RSA(), ENGINE_get_default_cipher_engine(), etc.
266       These are discussed in the next section, though they are not usually
267       required by application programmers as they are used automatically when
268       creating and using the relevant algorithm-specific types in OpenSSL,
269       such as RSA, DSA, EVP_CIPHER_CTX, etc.
270
271   Default implementations
272       For each supported abstraction, the ENGINE code maintains an internal
273       table of state to control which implementations are available for a
274       given abstraction and which should be used by default. These
275       implementations are registered in the tables and indexed by an 'nid'
276       value, because abstractions like EVP_CIPHER and EVP_DIGEST support many
277       distinct algorithms and modes, and ENGINEs can support arbitrarily many
278       of them.  In the case of other abstractions like RSA, DSA, etc, there
279       is only one "algorithm" so all implementations implicitly register
280       using the same 'nid' index.
281
282       When a default ENGINE is requested for a given
283       abstraction/algorithm/mode, (eg.  when calling RSA_new_method(NULL)), a
284       "get_default" call will be made to the ENGINE subsystem to process the
285       corresponding state table and return a functional reference to an
286       initialised ENGINE whose implementation should be used. If no ENGINE
287       should (or can) be used, it will return NULL and the caller will
288       operate with a NULL ENGINE handle - this usually equates to using the
289       conventional software implementation. In the latter case, OpenSSL will
290       from then on behave the way it used to before the ENGINE API existed.
291
292       Each state table has a flag to note whether it has processed this
293       "get_default" query since the table was last modified, because to
294       process this question it must iterate across all the registered ENGINEs
295       in the table trying to initialise each of them in turn, in case one of
296       them is operational. If it returns a functional reference to an ENGINE,
297       it will also cache another reference to speed up processing future
298       queries (without needing to iterate across the table). Likewise, it
299       will cache a NULL response if no ENGINE was available so that future
300       queries won't repeat the same iteration unless the state table changes.
301       This behaviour can also be changed; if the ENGINE_TABLE_FLAG_NOINIT
302       flag is set (using ENGINE_set_table_flags()), no attempted
303       initialisations will take place, instead the only way for the state
304       table to return a non-NULL ENGINE to the "get_default" query will be if
305       one is expressly set in the table. Eg.  ENGINE_set_default_RSA() does
306       the same job as ENGINE_register_RSA() except that it also sets the
307       state table's cached response for the "get_default" query. In the case
308       of abstractions like EVP_CIPHER, where implementations are indexed by
309       'nid', these flags and cached-responses are distinct for each 'nid'
310       value.
311
312   Application requirements
313       This section will explain the basic things an application programmer
314       should support to make the most useful elements of the ENGINE
315       functionality available to the user. The first thing to consider is
316       whether the programmer wishes to make alternative ENGINE modules
317       available to the application and user. OpenSSL maintains an internal
318       linked list of "visible" ENGINEs from which it has to operate - at
319       start-up, this list is empty and in fact if an application does not
320       call any ENGINE API calls and it uses static linking against openssl,
321       then the resulting application binary will not contain any alternative
322       ENGINE code at all. So the first consideration is whether any/all
323       available ENGINE implementations should be made visible to OpenSSL -
324       this is controlled by calling the various "load" functions, eg.
325
326        /* Make the "dynamic" ENGINE available */
327        void ENGINE_load_dynamic(void);
328        /* Make the CryptoSwift hardware acceleration support available */
329        void ENGINE_load_cswift(void);
330        /* Make support for nCipher's "CHIL" hardware available */
331        void ENGINE_load_chil(void);
332        ...
333        /* Make ALL ENGINE implementations bundled with OpenSSL available */
334        void ENGINE_load_builtin_engines(void);
335
336       Having called any of these functions, ENGINE objects would have been
337       dynamically allocated and populated with these implementations and
338       linked into OpenSSL's internal linked list. At this point it is
339       important to mention an important API function;
340
341        void ENGINE_cleanup(void);
342
343       If no ENGINE API functions are called at all in an application, then
344       there are no inherent memory leaks to worry about from the ENGINE
345       functionality, however if any ENGINEs are loaded, even if they are
346       never registered or used, it is necessary to use the ENGINE_cleanup()
347       function to correspondingly cleanup before program exit, if the caller
348       wishes to avoid memory leaks. This mechanism uses an internal callback
349       registration table so that any ENGINE API functionality that knows it
350       requires cleanup can register its cleanup details to be called during
351       ENGINE_cleanup(). This approach allows ENGINE_cleanup() to clean up
352       after any ENGINE functionality at all that your program uses, yet
353       doesn't automatically create linker dependencies to all possible ENGINE
354       functionality - only the cleanup callbacks required by the
355       functionality you do use will be required by the linker.
356
357       The fact that ENGINEs are made visible to OpenSSL (and thus are linked
358       into the program and loaded into memory at run-time) does not mean they
359       are "registered" or called into use by OpenSSL automatically - that
360       behaviour is something for the application to control. Some
361       applications will want to allow the user to specify exactly which
362       ENGINE they want used if any is to be used at all. Others may prefer to
363       load all support and have OpenSSL automatically use at run-time any
364       ENGINE that is able to successfully initialise - ie. to assume that
365       this corresponds to acceleration hardware attached to the machine or
366       some such thing. There are probably numerous other ways in which
367       applications may prefer to handle things, so we will simply illustrate
368       the consequences as they apply to a couple of simple cases and leave
369       developers to consider these and the source code to openssl's builtin
370       utilities as guides.
371
372       Using a specific ENGINE implementation
373
374       Here we'll assume an application has been configured by its user or
375       admin to want to use the "ACME" ENGINE if it is available in the
376       version of OpenSSL the application was compiled with. If it is
377       available, it should be used by default for all RSA, DSA, and symmetric
378       cipher operations, otherwise OpenSSL should use its builtin software as
379       per usual. The following code illustrates how to approach this;
380
381        ENGINE *e;
382        const char *engine_id = "ACME";
383        ENGINE_load_builtin_engines();
384        e = ENGINE_by_id(engine_id);
385        if(!e)
386            /* the engine isn't available */
387            return;
388        if(!ENGINE_init(e)) {
389            /* the engine couldn't initialise, release 'e' */
390            ENGINE_free(e);
391            return;
392        }
393        if(!ENGINE_set_default_RSA(e))
394            /* This should only happen when 'e' can't initialise, but the previous
395             * statement suggests it did. */
396            abort();
397        ENGINE_set_default_DSA(e);
398        ENGINE_set_default_ciphers(e);
399        /* Release the functional reference from ENGINE_init() */
400        ENGINE_finish(e);
401        /* Release the structural reference from ENGINE_by_id() */
402        ENGINE_free(e);
403
404       Automatically using builtin ENGINE implementations
405
406       Here we'll assume we want to load and register all ENGINE
407       implementations bundled with OpenSSL, such that for any cryptographic
408       algorithm required by OpenSSL - if there is an ENGINE that implements
409       it and can be initialised, it should be used. The following code
410       illustrates how this can work;
411
412        /* Load all bundled ENGINEs into memory and make them visible */
413        ENGINE_load_builtin_engines();
414        /* Register all of them for every algorithm they collectively implement */
415        ENGINE_register_all_complete();
416
417       That's all that's required. Eg. the next time OpenSSL tries to set up
418       an RSA key, any bundled ENGINEs that implement RSA_METHOD will be
419       passed to ENGINE_init() and if any of those succeed, that ENGINE will
420       be set as the default for RSA use from then on.
421
422   Advanced configuration support
423       There is a mechanism supported by the ENGINE framework that allows each
424       ENGINE implementation to define an arbitrary set of configuration
425       "commands" and expose them to OpenSSL and any applications based on
426       OpenSSL. This mechanism is entirely based on the use of name-value
427       pairs and assumes ASCII input (no unicode or UTF for now!), so it is
428       ideal if applications want to provide a transparent way for users to
429       provide arbitrary configuration "directives" directly to such ENGINEs.
430       It is also possible for the application to dynamically interrogate the
431       loaded ENGINE implementations for the names, descriptions, and input
432       flags of their available "control commands", providing a more flexible
433       configuration scheme. However, if the user is expected to know which
434       ENGINE device he/she is using (in the case of specialised hardware,
435       this goes without saying) then applications may not need to concern
436       themselves with discovering the supported control commands and simply
437       prefer to pass settings into ENGINEs exactly as they are provided by
438       the user.
439
440       Before illustrating how control commands work, it is worth mentioning
441       what they are typically used for. Broadly speaking there are two uses
442       for control commands; the first is to provide the necessary details to
443       the implementation (which may know nothing at all specific to the host
444       system) so that it can be initialised for use. This could include the
445       path to any driver or config files it needs to load, required network
446       addresses, smart-card identifiers, passwords to initialise protected
447       devices, logging information, etc etc. This class of commands typically
448       needs to be passed to an ENGINE before attempting to initialise it, ie.
449       before calling ENGINE_init(). The other class of commands consist of
450       settings or operations that tweak certain behaviour or cause certain
451       operations to take place, and these commands may work either before or
452       after ENGINE_init(), or in some cases both. ENGINE implementations
453       should provide indications of this in the descriptions attached to
454       builtin control commands and/or in external product documentation.
455
456       Issuing control commands to an ENGINE
457
458       Let's illustrate by example; a function for which the caller supplies
459       the name of the ENGINE it wishes to use, a table of string-pairs for
460       use before initialisation, and another table for use after
461       initialisation. Note that the string-pairs used for control commands
462       consist of a command "name" followed by the command "parameter" - the
463       parameter could be NULL in some cases but the name can not. This
464       function should initialise the ENGINE (issuing the "pre" commands
465       beforehand and the "post" commands afterwards) and set it as the
466       default for everything except RAND and then return a boolean success or
467       failure.
468
469        int generic_load_engine_fn(const char *engine_id,
470                                   const char **pre_cmds, int pre_num,
471                                   const char **post_cmds, int post_num)
472        {
473            ENGINE *e = ENGINE_by_id(engine_id);
474            if(!e) return 0;
475            while(pre_num--) {
476                if(!ENGINE_ctrl_cmd_string(e, pre_cmds[0], pre_cmds[1], 0)) {
477                    fprintf(stderr, "Failed command (%s - %s:%s)\n", engine_id,
478                        pre_cmds[0], pre_cmds[1] ? pre_cmds[1] : "(NULL)");
479                    ENGINE_free(e);
480                    return 0;
481                }
482                pre_cmds += 2;
483            }
484            if(!ENGINE_init(e)) {
485                fprintf(stderr, "Failed initialisation\n");
486                ENGINE_free(e);
487                return 0;
488            }
489            /* ENGINE_init() returned a functional reference, so free the structural
490             * reference from ENGINE_by_id(). */
491            ENGINE_free(e);
492            while(post_num--) {
493                if(!ENGINE_ctrl_cmd_string(e, post_cmds[0], post_cmds[1], 0)) {
494                    fprintf(stderr, "Failed command (%s - %s:%s)\n", engine_id,
495                        post_cmds[0], post_cmds[1] ? post_cmds[1] : "(NULL)");
496                    ENGINE_finish(e);
497                    return 0;
498                }
499                post_cmds += 2;
500            }
501            ENGINE_set_default(e, ENGINE_METHOD_ALL & ~ENGINE_METHOD_RAND);
502            /* Success */
503            return 1;
504        }
505
506       Note that ENGINE_ctrl_cmd_string() accepts a boolean argument that can
507       relax the semantics of the function - if set non-zero it will only
508       return failure if the ENGINE supported the given command name but
509       failed while executing it, if the ENGINE doesn't support the command
510       name it will simply return success without doing anything. In this case
511       we assume the user is only supplying commands specific to the given
512       ENGINE so we set this to FALSE.
513
514       Discovering supported control commands
515
516       It is possible to discover at run-time the names, numerical-ids,
517       descriptions and input parameters of the control commands supported by
518       an ENGINE using a structural reference. Note that some control commands
519       are defined by OpenSSL itself and it will intercept and handle these
520       control commands on behalf of the ENGINE, ie. the ENGINE's ctrl()
521       handler is not used for the control command.  openssl/engine.h defines
522       an index, ENGINE_CMD_BASE, that all control commands implemented by
523       ENGINEs should be numbered from. Any command value lower than this
524       symbol is considered a "generic" command is handled directly by the
525       OpenSSL core routines.
526
527       It is using these "core" control commands that one can discover the the
528       control commands implemented by a given ENGINE, specifically the
529       commands;
530
531        #define ENGINE_HAS_CTRL_FUNCTION               10
532        #define ENGINE_CTRL_GET_FIRST_CMD_TYPE         11
533        #define ENGINE_CTRL_GET_NEXT_CMD_TYPE          12
534        #define ENGINE_CTRL_GET_CMD_FROM_NAME          13
535        #define ENGINE_CTRL_GET_NAME_LEN_FROM_CMD      14
536        #define ENGINE_CTRL_GET_NAME_FROM_CMD          15
537        #define ENGINE_CTRL_GET_DESC_LEN_FROM_CMD      16
538        #define ENGINE_CTRL_GET_DESC_FROM_CMD          17
539        #define ENGINE_CTRL_GET_CMD_FLAGS              18
540
541       Whilst these commands are automatically processed by the OpenSSL
542       framework code, they use various properties exposed by each ENGINE to
543       process these queries. An ENGINE has 3 properties it exposes that can
544       affect how this behaves; it can supply a ctrl() handler, it can specify
545       ENGINE_FLAGS_MANUAL_CMD_CTRL in the ENGINE's flags, and it can expose
546       an array of control command descriptions.  If an ENGINE specifies the
547       ENGINE_FLAGS_MANUAL_CMD_CTRL flag, then it will simply pass all these
548       "core" control commands directly to the ENGINE's ctrl() handler (and
549       thus, it must have supplied one), so it is up to the ENGINE to reply to
550       these "discovery" commands itself. If that flag is not set, then the
551       OpenSSL framework code will work with the following rules;
552
553        if no ctrl() handler supplied;
554            ENGINE_HAS_CTRL_FUNCTION returns FALSE (zero),
555            all other commands fail.
556        if a ctrl() handler was supplied but no array of control commands;
557            ENGINE_HAS_CTRL_FUNCTION returns TRUE,
558            all other commands fail.
559        if a ctrl() handler and array of control commands was supplied;
560            ENGINE_HAS_CTRL_FUNCTION returns TRUE,
561            all other commands proceed processing ...
562
563       If the ENGINE's array of control commands is empty then all other
564       commands will fail, otherwise; ENGINE_CTRL_GET_FIRST_CMD_TYPE returns
565       the identifier of the first command supported by the ENGINE,
566       ENGINE_GET_NEXT_CMD_TYPE takes the identifier of a command supported by
567       the ENGINE and returns the next command identifier or fails if there
568       are no more, ENGINE_CMD_FROM_NAME takes a string name for a command and
569       returns the corresponding identifier or fails if no such command name
570       exists, and the remaining commands take a command identifier and return
571       properties of the corresponding commands. All except
572       ENGINE_CTRL_GET_FLAGS return the string length of a command name or
573       description, or populate a supplied character buffer with a copy of the
574       command name or description. ENGINE_CTRL_GET_FLAGS returns a bitwise-
575       OR'd mask of the following possible values;
576
577        #define ENGINE_CMD_FLAG_NUMERIC                (unsigned int)0x0001
578        #define ENGINE_CMD_FLAG_STRING                 (unsigned int)0x0002
579        #define ENGINE_CMD_FLAG_NO_INPUT               (unsigned int)0x0004
580        #define ENGINE_CMD_FLAG_INTERNAL               (unsigned int)0x0008
581
582       If the ENGINE_CMD_FLAG_INTERNAL flag is set, then any other flags are
583       purely informational to the caller - this flag will prevent the command
584       being usable for any higher-level ENGINE functions such as
585       ENGINE_ctrl_cmd_string().  "INTERNAL" commands are not intended to be
586       exposed to text-based configuration by applications, administrations,
587       users, etc. These can support arbitrary operations via ENGINE_ctrl(),
588       including passing to and/or from the control commands data of any
589       arbitrary type. These commands are supported in the discovery
590       mechanisms simply to allow applications determinie if an ENGINE
591       supports certain specific commands it might want to use (eg.
592       application "foo" might query various ENGINEs to see if they implement
593       "FOO_GET_VENDOR_LOGO_GIF" - and ENGINE could therefore decide whether
594       or not to support this "foo"-specific extension).
595
596   Future developments
597       The ENGINE API and internal architecture is currently being reviewed.
598       Slated for possible release in 0.9.8 is support for transparent loading
599       of "dynamic" ENGINEs (built as self-contained shared-libraries). This
600       would allow ENGINE implementations to be provided independently of
601       OpenSSL libraries and/or OpenSSL-based applications, and would also
602       remove any requirement for applications to explicitly use the "dynamic"
603       ENGINE to bind to shared-library implementations.
604

SEE ALSO

606       rsa(3), dsa(3), dh(3), rand(3)
607
608
609
6101.0.2o                            2020-08-01                         engine(3)
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