5 ENGINE_get_DH, ENGINE_get_DSA, ENGINE_get_ECDH, ENGINE_get_ECDSA,
6 ENGINE_by_id, ENGINE_get_cipher_engine, ENGINE_get_default_DH,
7 ENGINE_get_default_DSA, ENGINE_get_default_ECDH,
8 ENGINE_get_default_ECDSA, ENGINE_get_default_RAND,
9 ENGINE_get_default_RSA, ENGINE_get_digest_engine, ENGINE_get_first,
10 ENGINE_get_last, ENGINE_get_next, ENGINE_get_prev, ENGINE_new,
11 ENGINE_get_ciphers, ENGINE_get_ctrl_function, ENGINE_get_digests,
12 ENGINE_get_destroy_function, ENGINE_get_finish_function,
13 ENGINE_get_init_function, ENGINE_get_load_privkey_function,
14 ENGINE_get_load_pubkey_function, ENGINE_load_private_key,
15 ENGINE_load_public_key, ENGINE_get_RAND, ENGINE_get_RSA, ENGINE_get_id,
16 ENGINE_get_name, ENGINE_get_cmd_defns, EVP_CIPHER ENGINE_get_cipher,
17 ENGINE_get_digest, ENGINE_add, ENGINE_cmd_is_executable,
18 ENGINE_ctrl, ENGINE_ctrl_cmd, ENGINE_ctrl_cmd_string,
19 ENGINE_finish, ENGINE_free, ENGINE_get_flags, ENGINE_init,
20 ENGINE_register_DH, ENGINE_register_DSA, ENGINE_register_ECDH,
21 ENGINE_register_ECDSA, ENGINE_register_RAND, ENGINE_register_RSA,
22 ENGINE_register_all_complete, ENGINE_register_ciphers,
23 ENGINE_register_complete, ENGINE_register_digests, ENGINE_remove,
24 ENGINE_set_DH, ENGINE_set_DSA, ENGINE_set_ECDH, ENGINE_set_ECDSA,
25 ENGINE_set_RAND, ENGINE_set_RSA, ENGINE_set_ciphers,
26 ENGINE_set_cmd_defns, ENGINE_set_ctrl_function, ENGINE_set_default,
27 ENGINE_set_default_DH, ENGINE_set_default_DSA, ENGINE_set_default_ECDH,
28 ENGINE_set_default_ECDSA, ENGINE_set_default_RAND, ENGINE_set_default_RSA,
29 ENGINE_set_default_ciphers, ENGINE_set_default_digests,
30 ENGINE_set_default_string, ENGINE_set_destroy_function,
31 ENGINE_set_digests, ENGINE_set_finish_function, ENGINE_set_flags,
32 ENGINE_set_id, ENGINE_set_init_function, ENGINE_set_load_privkey_function,
33 ENGINE_set_load_pubkey_function, ENGINE_set_name, ENGINE_up_ref,
34 ENGINE_get_table_flags, ENGINE_cleanup,
35 ENGINE_load_builtin_engines, ENGINE_register_all_DH,
36 ENGINE_register_all_DSA, ENGINE_register_all_ECDH,
37 ENGINE_register_all_ECDSA, ENGINE_register_all_RAND,
38 ENGINE_register_all_RSA, ENGINE_register_all_ciphers,
39 ENGINE_register_all_digests, ENGINE_set_table_flags, ENGINE_unregister_DH,
40 ENGINE_unregister_DSA, ENGINE_unregister_ECDH, ENGINE_unregister_ECDSA,
41 ENGINE_unregister_RAND, ENGINE_unregister_RSA, ENGINE_unregister_ciphers,
42 ENGINE_unregister_digests
43 - ENGINE cryptographic module support
47 #include <openssl/engine.h>
49 ENGINE *ENGINE_get_first(void);
50 ENGINE *ENGINE_get_last(void);
51 ENGINE *ENGINE_get_next(ENGINE *e);
52 ENGINE *ENGINE_get_prev(ENGINE *e);
54 int ENGINE_add(ENGINE *e);
55 int ENGINE_remove(ENGINE *e);
57 ENGINE *ENGINE_by_id(const char *id);
59 int ENGINE_init(ENGINE *e);
60 int ENGINE_finish(ENGINE *e);
62 void ENGINE_load_builtin_engines(void);
64 ENGINE *ENGINE_get_default_RSA(void);
65 ENGINE *ENGINE_get_default_DSA(void);
66 ENGINE *ENGINE_get_default_ECDH(void);
67 ENGINE *ENGINE_get_default_ECDSA(void);
68 ENGINE *ENGINE_get_default_DH(void);
69 ENGINE *ENGINE_get_default_RAND(void);
70 ENGINE *ENGINE_get_cipher_engine(int nid);
71 ENGINE *ENGINE_get_digest_engine(int nid);
73 int ENGINE_set_default_RSA(ENGINE *e);
74 int ENGINE_set_default_DSA(ENGINE *e);
75 int ENGINE_set_default_ECDH(ENGINE *e);
76 int ENGINE_set_default_ECDSA(ENGINE *e);
77 int ENGINE_set_default_DH(ENGINE *e);
78 int ENGINE_set_default_RAND(ENGINE *e);
79 int ENGINE_set_default_ciphers(ENGINE *e);
80 int ENGINE_set_default_digests(ENGINE *e);
81 int ENGINE_set_default_string(ENGINE *e, const char *list);
83 int ENGINE_set_default(ENGINE *e, unsigned int flags);
85 unsigned int ENGINE_get_table_flags(void);
86 void ENGINE_set_table_flags(unsigned int flags);
88 int ENGINE_register_RSA(ENGINE *e);
89 void ENGINE_unregister_RSA(ENGINE *e);
90 void ENGINE_register_all_RSA(void);
91 int ENGINE_register_DSA(ENGINE *e);
92 void ENGINE_unregister_DSA(ENGINE *e);
93 void ENGINE_register_all_DSA(void);
94 int ENGINE_register_ECDH(ENGINE *e);
95 void ENGINE_unregister_ECDH(ENGINE *e);
96 void ENGINE_register_all_ECDH(void);
97 int ENGINE_register_ECDSA(ENGINE *e);
98 void ENGINE_unregister_ECDSA(ENGINE *e);
99 void ENGINE_register_all_ECDSA(void);
100 int ENGINE_register_DH(ENGINE *e);
101 void ENGINE_unregister_DH(ENGINE *e);
102 void ENGINE_register_all_DH(void);
103 int ENGINE_register_RAND(ENGINE *e);
104 void ENGINE_unregister_RAND(ENGINE *e);
105 void ENGINE_register_all_RAND(void);
106 int ENGINE_register_ciphers(ENGINE *e);
107 void ENGINE_unregister_ciphers(ENGINE *e);
108 void ENGINE_register_all_ciphers(void);
109 int ENGINE_register_digests(ENGINE *e);
110 void ENGINE_unregister_digests(ENGINE *e);
111 void ENGINE_register_all_digests(void);
112 int ENGINE_register_complete(ENGINE *e);
113 int ENGINE_register_all_complete(void);
115 int ENGINE_ctrl(ENGINE *e, int cmd, long i, void *p, void (*f)(void));
116 int ENGINE_cmd_is_executable(ENGINE *e, int cmd);
117 int ENGINE_ctrl_cmd(ENGINE *e, const char *cmd_name,
118 long i, void *p, void (*f)(void), int cmd_optional);
119 int ENGINE_ctrl_cmd_string(ENGINE *e, const char *cmd_name, const char *arg,
122 ENGINE *ENGINE_new(void);
123 int ENGINE_free(ENGINE *e);
124 int ENGINE_up_ref(ENGINE *e);
126 int ENGINE_set_id(ENGINE *e, const char *id);
127 int ENGINE_set_name(ENGINE *e, const char *name);
128 int ENGINE_set_RSA(ENGINE *e, const RSA_METHOD *rsa_meth);
129 int ENGINE_set_DSA(ENGINE *e, const DSA_METHOD *dsa_meth);
130 int ENGINE_set_ECDH(ENGINE *e, const ECDH_METHOD *dh_meth);
131 int ENGINE_set_ECDSA(ENGINE *e, const ECDSA_METHOD *dh_meth);
132 int ENGINE_set_DH(ENGINE *e, const DH_METHOD *dh_meth);
133 int ENGINE_set_RAND(ENGINE *e, const RAND_METHOD *rand_meth);
134 int ENGINE_set_destroy_function(ENGINE *e, ENGINE_GEN_INT_FUNC_PTR destroy_f);
135 int ENGINE_set_init_function(ENGINE *e, ENGINE_GEN_INT_FUNC_PTR init_f);
136 int ENGINE_set_finish_function(ENGINE *e, ENGINE_GEN_INT_FUNC_PTR finish_f);
137 int ENGINE_set_ctrl_function(ENGINE *e, ENGINE_CTRL_FUNC_PTR ctrl_f);
138 int ENGINE_set_load_privkey_function(ENGINE *e, ENGINE_LOAD_KEY_PTR loadpriv_f);
139 int ENGINE_set_load_pubkey_function(ENGINE *e, ENGINE_LOAD_KEY_PTR loadpub_f);
140 int ENGINE_set_ciphers(ENGINE *e, ENGINE_CIPHERS_PTR f);
141 int ENGINE_set_digests(ENGINE *e, ENGINE_DIGESTS_PTR f);
142 int ENGINE_set_flags(ENGINE *e, int flags);
143 int ENGINE_set_cmd_defns(ENGINE *e, const ENGINE_CMD_DEFN *defns);
145 const char *ENGINE_get_id(const ENGINE *e);
146 const char *ENGINE_get_name(const ENGINE *e);
147 const RSA_METHOD *ENGINE_get_RSA(const ENGINE *e);
148 const DSA_METHOD *ENGINE_get_DSA(const ENGINE *e);
149 const ECDH_METHOD *ENGINE_get_ECDH(const ENGINE *e);
150 const ECDSA_METHOD *ENGINE_get_ECDSA(const ENGINE *e);
151 const DH_METHOD *ENGINE_get_DH(const ENGINE *e);
152 const RAND_METHOD *ENGINE_get_RAND(const ENGINE *e);
153 ENGINE_GEN_INT_FUNC_PTR ENGINE_get_destroy_function(const ENGINE *e);
154 ENGINE_GEN_INT_FUNC_PTR ENGINE_get_init_function(const ENGINE *e);
155 ENGINE_GEN_INT_FUNC_PTR ENGINE_get_finish_function(const ENGINE *e);
156 ENGINE_CTRL_FUNC_PTR ENGINE_get_ctrl_function(const ENGINE *e);
157 ENGINE_LOAD_KEY_PTR ENGINE_get_load_privkey_function(const ENGINE *e);
158 ENGINE_LOAD_KEY_PTR ENGINE_get_load_pubkey_function(const ENGINE *e);
159 ENGINE_CIPHERS_PTR ENGINE_get_ciphers(const ENGINE *e);
160 ENGINE_DIGESTS_PTR ENGINE_get_digests(const ENGINE *e);
161 const EVP_CIPHER *ENGINE_get_cipher(ENGINE *e, int nid);
162 const EVP_MD *ENGINE_get_digest(ENGINE *e, int nid);
163 int ENGINE_get_flags(const ENGINE *e);
164 const ENGINE_CMD_DEFN *ENGINE_get_cmd_defns(const ENGINE *e);
166 EVP_PKEY *ENGINE_load_private_key(ENGINE *e, const char *key_id,
167 UI_METHOD *ui_method, void *callback_data);
168 EVP_PKEY *ENGINE_load_public_key(ENGINE *e, const char *key_id,
169 UI_METHOD *ui_method, void *callback_data);
173 #if OPENSSL_API_COMPAT < 0x10100000L
174 void ENGINE_cleanup(void)
179 These functions create, manipulate, and use cryptographic modules in the
180 form of B<ENGINE> objects. These objects act as containers for
181 implementations of cryptographic algorithms, and support a
182 reference-counted mechanism to allow them to be dynamically loaded in and
183 out of the running application.
185 The cryptographic functionality that can be provided by an B<ENGINE>
186 implementation includes the following abstractions;
188 RSA_METHOD - for providing alternative RSA implementations
189 DSA_METHOD, DH_METHOD, RAND_METHOD, ECDH_METHOD, ECDSA_METHOD,
190 - similarly for other OpenSSL APIs
191 EVP_CIPHER - potentially multiple cipher algorithms (indexed by 'nid')
192 EVP_DIGEST - potentially multiple hash algorithms (indexed by 'nid')
193 key-loading - loading public and/or private EVP_PKEY keys
195 =head2 Reference counting and handles
197 Due to the modular nature of the ENGINE API, pointers to ENGINEs need to be
198 treated as handles - ie. not only as pointers, but also as references to
199 the underlying ENGINE object. Ie. one should obtain a new reference when
200 making copies of an ENGINE pointer if the copies will be used (and
201 released) independently.
203 ENGINE objects have two levels of reference-counting to match the way in
204 which the objects are used. At the most basic level, each ENGINE pointer is
205 inherently a B<structural> reference - a structural reference is required
206 to use the pointer value at all, as this kind of reference is a guarantee
207 that the structure can not be deallocated until the reference is released.
209 However, a structural reference provides no guarantee that the ENGINE is
210 initialised and able to use any of its cryptographic
211 implementations. Indeed it's quite possible that most ENGINEs will not
212 initialise at all in typical environments, as ENGINEs are typically used to
213 support specialised hardware. To use an ENGINE's functionality, you need a
214 B<functional> reference. This kind of reference can be considered a
215 specialised form of structural reference, because each functional reference
216 implicitly contains a structural reference as well - however to avoid
217 difficult-to-find programming bugs, it is recommended to treat the two
218 kinds of reference independently. If you have a functional reference to an
219 ENGINE, you have a guarantee that the ENGINE has been initialised and
220 is ready to perform cryptographic operations, and will remain initialised
221 until after you have released your reference.
223 I<Structural references>
225 This basic type of reference is used for instantiating new ENGINEs,
226 iterating across OpenSSL's internal linked-list of loaded
227 ENGINEs, reading information about an ENGINE, etc. Essentially a structural
228 reference is sufficient if you only need to query or manipulate the data of
229 an ENGINE implementation rather than use its functionality.
231 The ENGINE_new() function returns a structural reference to a new (empty)
232 ENGINE object. There are other ENGINE API functions that return structural
233 references such as; ENGINE_by_id(), ENGINE_get_first(), ENGINE_get_last(),
234 ENGINE_get_next(), ENGINE_get_prev(). All structural references should be
235 released by a corresponding to call to the ENGINE_free() function - the
236 ENGINE object itself will only actually be cleaned up and deallocated when
237 the last structural reference is released.
239 It should also be noted that many ENGINE API function calls that accept a
240 structural reference will internally obtain another reference - typically
241 this happens whenever the supplied ENGINE will be needed by OpenSSL after
242 the function has returned. Eg. the function to add a new ENGINE to
243 OpenSSL's internal list is ENGINE_add() - if this function returns success,
244 then OpenSSL will have stored a new structural reference internally so the
245 caller is still responsible for freeing their own reference with
246 ENGINE_free() when they are finished with it. In a similar way, some
247 functions will automatically release the structural reference passed to it
248 if part of the function's job is to do so. Eg. the ENGINE_get_next() and
249 ENGINE_get_prev() functions are used for iterating across the internal
250 ENGINE list - they will return a new structural reference to the next (or
251 previous) ENGINE in the list or NULL if at the end (or beginning) of the
252 list, but in either case the structural reference passed to the function is
253 released on behalf of the caller.
255 To clarify a particular function's handling of references, one should
256 always consult that function's documentation "man" page, or failing that
257 the openssl/engine.h header file includes some hints.
259 I<Functional references>
261 As mentioned, functional references exist when the cryptographic
262 functionality of an ENGINE is required to be available. A functional
263 reference can be obtained in one of two ways; from an existing structural
264 reference to the required ENGINE, or by asking OpenSSL for the default
265 operational ENGINE for a given cryptographic purpose.
267 To obtain a functional reference from an existing structural reference,
268 call the ENGINE_init() function. This returns zero if the ENGINE was not
269 already operational and couldn't be successfully initialised (eg. lack of
270 system drivers, no special hardware attached, etc), otherwise it will
271 return non-zero to indicate that the ENGINE is now operational and will
272 have allocated a new B<functional> reference to the ENGINE. All functional
273 references are released by calling ENGINE_finish() (which removes the
274 implicit structural reference as well).
276 The second way to get a functional reference is by asking OpenSSL for a
277 default implementation for a given task, eg. by ENGINE_get_default_RSA(),
278 ENGINE_get_default_cipher_engine(), etc. These are discussed in the next
279 section, though they are not usually required by application programmers as
280 they are used automatically when creating and using the relevant
281 algorithm-specific types in OpenSSL, such as RSA, DSA, EVP_CIPHER_CTX, etc.
283 =head2 Default implementations
285 For each supported abstraction, the ENGINE code maintains an internal table
286 of state to control which implementations are available for a given
287 abstraction and which should be used by default. These implementations are
288 registered in the tables and indexed by an 'nid' value, because
289 abstractions like EVP_CIPHER and EVP_DIGEST support many distinct
290 algorithms and modes, and ENGINEs can support arbitrarily many of them.
291 In the case of other abstractions like RSA, DSA, etc, there is only one
292 "algorithm" so all implementations implicitly register using the same 'nid'
295 When a default ENGINE is requested for a given abstraction/algorithm/mode, (eg.
296 when calling RSA_new_method(NULL)), a "get_default" call will be made to the
297 ENGINE subsystem to process the corresponding state table and return a
298 functional reference to an initialised ENGINE whose implementation should be
299 used. If no ENGINE should (or can) be used, it will return NULL and the caller
300 will operate with a NULL ENGINE handle - this usually equates to using the
301 conventional software implementation. In the latter case, OpenSSL will from
302 then on behave the way it used to before the ENGINE API existed.
304 Each state table has a flag to note whether it has processed this
305 "get_default" query since the table was last modified, because to process
306 this question it must iterate across all the registered ENGINEs in the
307 table trying to initialise each of them in turn, in case one of them is
308 operational. If it returns a functional reference to an ENGINE, it will
309 also cache another reference to speed up processing future queries (without
310 needing to iterate across the table). Likewise, it will cache a NULL
311 response if no ENGINE was available so that future queries won't repeat the
312 same iteration unless the state table changes. This behaviour can also be
313 changed; if the ENGINE_TABLE_FLAG_NOINIT flag is set (using
314 ENGINE_set_table_flags()), no attempted initialisations will take place,
315 instead the only way for the state table to return a non-NULL ENGINE to the
316 "get_default" query will be if one is expressly set in the table. Eg.
317 ENGINE_set_default_RSA() does the same job as ENGINE_register_RSA() except
318 that it also sets the state table's cached response for the "get_default"
319 query. In the case of abstractions like EVP_CIPHER, where implementations are
320 indexed by 'nid', these flags and cached-responses are distinct for each 'nid'
323 =head2 Application requirements
325 This section will explain the basic things an application programmer should
326 support to make the most useful elements of the ENGINE functionality
327 available to the user. The first thing to consider is whether the
328 programmer wishes to make alternative ENGINE modules available to the
329 application and user. OpenSSL maintains an internal linked list of
330 "visible" ENGINEs from which it has to operate - at start-up, this list is
331 empty and in fact if an application does not call any ENGINE API calls and
332 it uses static linking against openssl, then the resulting application
333 binary will not contain any alternative ENGINE code at all. So the first
334 consideration is whether any/all available ENGINE implementations should be
335 made visible to OpenSSL - this is controlled by calling the various "load"
338 Having called any of these functions, ENGINE objects would have been
339 dynamically allocated and populated with these implementations and linked
340 into OpenSSL's internal linked list. At this point it is important to
341 mention an important API function;
343 void ENGINE_cleanup(void)
345 If no ENGINE API functions are called at all in an application, then there
346 are no inherent memory leaks to worry about from the ENGINE functionality.
347 However, prior to OpenSSL 1.1.0 if any ENGINEs are loaded, even if they are
348 never registered or used, it was necessary to use the ENGINE_cleanup() function
349 to correspondingly cleanup before program exit, if the caller wishes to avoid
350 memory leaks. This mechanism used an internal callback registration table
351 so that any ENGINE API functionality that knows it requires cleanup can
352 register its cleanup details to be called during ENGINE_cleanup(). This
353 approach allowed ENGINE_cleanup() to clean up after any ENGINE functionality
354 at all that your program uses, yet doesn't automatically create linker
355 dependencies to all possible ENGINE functionality - only the cleanup
356 callbacks required by the functionality you do use will be required by the
357 linker. From OpenSSL 1.1.0 it is no longer necessary to explicitly call
358 ENGINE_cleanup and this function is deprecated. Cleanup automatically takes
359 place at program exit.
361 The fact that ENGINEs are made visible to OpenSSL (and thus are linked into
362 the program and loaded into memory at run-time) does not mean they are
363 "registered" or called into use by OpenSSL automatically - that behaviour
364 is something for the application to control. Some applications
365 will want to allow the user to specify exactly which ENGINE they want used
366 if any is to be used at all. Others may prefer to load all support and have
367 OpenSSL automatically use at run-time any ENGINE that is able to
368 successfully initialise - ie. to assume that this corresponds to
369 acceleration hardware attached to the machine or some such thing. There are
370 probably numerous other ways in which applications may prefer to handle
371 things, so we will simply illustrate the consequences as they apply to a
372 couple of simple cases and leave developers to consider these and the
373 source code to openssl's builtin utilities as guides.
375 I<Using a specific ENGINE implementation>
377 Here we'll assume an application has been configured by its user or admin
378 to want to use the "ACME" ENGINE if it is available in the version of
379 OpenSSL the application was compiled with. If it is available, it should be
380 used by default for all RSA, DSA, and symmetric cipher operations, otherwise
381 OpenSSL should use its builtin software as per usual. The following code
382 illustrates how to approach this;
385 const char *engine_id = "ACME";
386 ENGINE_load_builtin_engines();
387 e = ENGINE_by_id(engine_id);
389 /* the engine isn't available */
391 if(!ENGINE_init(e)) {
392 /* the engine couldn't initialise, release 'e' */
396 if(!ENGINE_set_default_RSA(e))
397 /* This should only happen when 'e' can't initialise, but the previous
398 * statement suggests it did. */
400 ENGINE_set_default_DSA(e);
401 ENGINE_set_default_ciphers(e);
402 /* Release the functional reference from ENGINE_init() */
404 /* Release the structural reference from ENGINE_by_id() */
407 I<Automatically using builtin ENGINE implementations>
409 Here we'll assume we want to load and register all ENGINE implementations
410 bundled with OpenSSL, such that for any cryptographic algorithm required by
411 OpenSSL - if there is an ENGINE that implements it and can be initialised,
412 it should be used. The following code illustrates how this can work;
414 /* Load all bundled ENGINEs into memory and make them visible */
415 ENGINE_load_builtin_engines();
416 /* Register all of them for every algorithm they collectively implement */
417 ENGINE_register_all_complete();
419 That's all that's required. Eg. the next time OpenSSL tries to set up an
420 RSA key, any bundled ENGINEs that implement RSA_METHOD will be passed to
421 ENGINE_init() and if any of those succeed, that ENGINE will be set as the
422 default for RSA use from then on.
424 =head2 Advanced configuration support
426 There is a mechanism supported by the ENGINE framework that allows each
427 ENGINE implementation to define an arbitrary set of configuration
428 "commands" and expose them to OpenSSL and any applications based on
429 OpenSSL. This mechanism is entirely based on the use of name-value pairs
430 and assumes ASCII input (no unicode or UTF for now!), so it is ideal if
431 applications want to provide a transparent way for users to provide
432 arbitrary configuration "directives" directly to such ENGINEs. It is also
433 possible for the application to dynamically interrogate the loaded ENGINE
434 implementations for the names, descriptions, and input flags of their
435 available "control commands", providing a more flexible configuration
436 scheme. However, if the user is expected to know which ENGINE device he/she
437 is using (in the case of specialised hardware, this goes without saying)
438 then applications may not need to concern themselves with discovering the
439 supported control commands and simply prefer to pass settings into ENGINEs
440 exactly as they are provided by the user.
442 Before illustrating how control commands work, it is worth mentioning what
443 they are typically used for. Broadly speaking there are two uses for
444 control commands; the first is to provide the necessary details to the
445 implementation (which may know nothing at all specific to the host system)
446 so that it can be initialised for use. This could include the path to any
447 driver or config files it needs to load, required network addresses,
448 smart-card identifiers, passwords to initialise protected devices,
449 logging information, etc etc. This class of commands typically needs to be
450 passed to an ENGINE B<before> attempting to initialise it, ie. before
451 calling ENGINE_init(). The other class of commands consist of settings or
452 operations that tweak certain behaviour or cause certain operations to take
453 place, and these commands may work either before or after ENGINE_init(), or
454 in some cases both. ENGINE implementations should provide indications of
455 this in the descriptions attached to builtin control commands and/or in
456 external product documentation.
458 I<Issuing control commands to an ENGINE>
460 Let's illustrate by example; a function for which the caller supplies the
461 name of the ENGINE it wishes to use, a table of string-pairs for use before
462 initialisation, and another table for use after initialisation. Note that
463 the string-pairs used for control commands consist of a command "name"
464 followed by the command "parameter" - the parameter could be NULL in some
465 cases but the name can not. This function should initialise the ENGINE
466 (issuing the "pre" commands beforehand and the "post" commands afterwards)
467 and set it as the default for everything except RAND and then return a
468 boolean success or failure.
470 int generic_load_engine_fn(const char *engine_id,
471 const char **pre_cmds, int pre_num,
472 const char **post_cmds, int post_num)
474 ENGINE *e = ENGINE_by_id(engine_id);
477 if(!ENGINE_ctrl_cmd_string(e, pre_cmds[0], pre_cmds[1], 0)) {
478 fprintf(stderr, "Failed command (%s - %s:%s)\n", engine_id,
479 pre_cmds[0], pre_cmds[1] ? pre_cmds[1] : "(NULL)");
485 if(!ENGINE_init(e)) {
486 fprintf(stderr, "Failed initialisation\n");
490 /* ENGINE_init() returned a functional reference, so free the structural
491 * reference from ENGINE_by_id(). */
494 if(!ENGINE_ctrl_cmd_string(e, post_cmds[0], post_cmds[1], 0)) {
495 fprintf(stderr, "Failed command (%s - %s:%s)\n", engine_id,
496 post_cmds[0], post_cmds[1] ? post_cmds[1] : "(NULL)");
502 ENGINE_set_default(e, ENGINE_METHOD_ALL & ~ENGINE_METHOD_RAND);
507 Note that ENGINE_ctrl_cmd_string() accepts a boolean argument that can
508 relax the semantics of the function - if set non-zero it will only return
509 failure if the ENGINE supported the given command name but failed while
510 executing it, if the ENGINE doesn't support the command name it will simply
511 return success without doing anything. In this case we assume the user is
512 only supplying commands specific to the given ENGINE so we set this to
515 I<Discovering supported control commands>
517 It is possible to discover at run-time the names, numerical-ids, descriptions
518 and input parameters of the control commands supported by an ENGINE using a
519 structural reference. Note that some control commands are defined by OpenSSL
520 itself and it will intercept and handle these control commands on behalf of the
521 ENGINE, ie. the ENGINE's ctrl() handler is not used for the control command.
522 openssl/engine.h defines an index, ENGINE_CMD_BASE, that all control commands
523 implemented by ENGINEs should be numbered from. Any command value lower than
524 this symbol is considered a "generic" command is handled directly by the
525 OpenSSL core routines.
527 It is using these "core" control commands that one can discover the control
528 commands implemented by a given ENGINE, specifically the commands;
530 #define ENGINE_HAS_CTRL_FUNCTION 10
531 #define ENGINE_CTRL_GET_FIRST_CMD_TYPE 11
532 #define ENGINE_CTRL_GET_NEXT_CMD_TYPE 12
533 #define ENGINE_CTRL_GET_CMD_FROM_NAME 13
534 #define ENGINE_CTRL_GET_NAME_LEN_FROM_CMD 14
535 #define ENGINE_CTRL_GET_NAME_FROM_CMD 15
536 #define ENGINE_CTRL_GET_DESC_LEN_FROM_CMD 16
537 #define ENGINE_CTRL_GET_DESC_FROM_CMD 17
538 #define ENGINE_CTRL_GET_CMD_FLAGS 18
540 Whilst these commands are automatically processed by the OpenSSL framework code,
541 they use various properties exposed by each ENGINE to process these
542 queries. An ENGINE has 3 properties it exposes that can affect how this behaves;
543 it can supply a ctrl() handler, it can specify ENGINE_FLAGS_MANUAL_CMD_CTRL in
544 the ENGINE's flags, and it can expose an array of control command descriptions.
545 If an ENGINE specifies the ENGINE_FLAGS_MANUAL_CMD_CTRL flag, then it will
546 simply pass all these "core" control commands directly to the ENGINE's ctrl()
547 handler (and thus, it must have supplied one), so it is up to the ENGINE to
548 reply to these "discovery" commands itself. If that flag is not set, then the
549 OpenSSL framework code will work with the following rules;
551 if no ctrl() handler supplied;
552 ENGINE_HAS_CTRL_FUNCTION returns FALSE (zero),
553 all other commands fail.
554 if a ctrl() handler was supplied but no array of control commands;
555 ENGINE_HAS_CTRL_FUNCTION returns TRUE,
556 all other commands fail.
557 if a ctrl() handler and array of control commands was supplied;
558 ENGINE_HAS_CTRL_FUNCTION returns TRUE,
559 all other commands proceed processing ...
561 If the ENGINE's array of control commands is empty then all other commands will
562 fail, otherwise; ENGINE_CTRL_GET_FIRST_CMD_TYPE returns the identifier of
563 the first command supported by the ENGINE, ENGINE_GET_NEXT_CMD_TYPE takes the
564 identifier of a command supported by the ENGINE and returns the next command
565 identifier or fails if there are no more, ENGINE_CMD_FROM_NAME takes a string
566 name for a command and returns the corresponding identifier or fails if no such
567 command name exists, and the remaining commands take a command identifier and
568 return properties of the corresponding commands. All except
569 ENGINE_CTRL_GET_FLAGS return the string length of a command name or description,
570 or populate a supplied character buffer with a copy of the command name or
571 description. ENGINE_CTRL_GET_FLAGS returns a bitwise-OR'd mask of the following
574 #define ENGINE_CMD_FLAG_NUMERIC (unsigned int)0x0001
575 #define ENGINE_CMD_FLAG_STRING (unsigned int)0x0002
576 #define ENGINE_CMD_FLAG_NO_INPUT (unsigned int)0x0004
577 #define ENGINE_CMD_FLAG_INTERNAL (unsigned int)0x0008
579 If the ENGINE_CMD_FLAG_INTERNAL flag is set, then any other flags are purely
580 informational to the caller - this flag will prevent the command being usable
581 for any higher-level ENGINE functions such as ENGINE_ctrl_cmd_string().
582 "INTERNAL" commands are not intended to be exposed to text-based configuration
583 by applications, administrations, users, etc. These can support arbitrary
584 operations via ENGINE_ctrl(), including passing to and/or from the control
585 commands data of any arbitrary type. These commands are supported in the
586 discovery mechanisms simply to allow applications to determine if an ENGINE
587 supports certain specific commands it might want to use (eg. application "foo"
588 might query various ENGINEs to see if they implement "FOO_GET_VENDOR_LOGO_GIF" -
589 and ENGINE could therefore decide whether or not to support this "foo"-specific
594 L<OPENSSL_init_crypto(3)>, L<RSA_new_method(3)>, L<dsa(3)>, L<dh(3)>, L<rand(3)>
598 ENGINE_cleanup(), ENGINE_load_openssl(), ENGINE_load_dynamic(), and
599 ENGINE_load_cryptodev() were deprecated in OpenSSL 1.1.0 by
600 OPENSSL_init_crypto().
604 Copyright 2002-2016 The OpenSSL Project Authors. All Rights Reserved.
606 Licensed under the OpenSSL license (the "License"). You may not use
607 this file except in compliance with the License. You can obtain a copy
608 in the file LICENSE in the source distribution or at
609 L<https://www.openssl.org/source/license.html>.