1engine(3) OpenSSL engine(3)
2
6 engine - ENGINE cryptographic module support
7
9 #include <openssl/engine.h>
10 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 int ENGINE_add(ENGINE *e);
17 int ENGINE_remove(ENGINE *e);
18 ENGINE *ENGINE_by_id(const char *id);
20 int ENGINE_init(ENGINE *e);
22 int ENGINE_finish(ENGINE *e);
23 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 void ENGINE_cleanup(void);
41 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 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 int ENGINE_set_default(ENGINE *e, unsigned int flags);
62 unsigned int ENGINE_get_table_flags(void);
64 void ENGINE_set_table_flags(unsigned int flags);
65 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 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 int ENGINE_set_ex_data(ENGINE *e, int idx, void *arg);
104 void *ENGINE_get_ex_data(const ENGINE *e, int idx);
105 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 ENGINE *ENGINE_new(void);
110 int ENGINE_free(ENGINE *e);
111 int ENGINE_up_ref(ENGINE *e);
112 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 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 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 void ENGINE_add_conf_module(void);
161
163 These functions create, manipulate, and use cryptographic modules in
164 the form of ENGINE objects. These objects act as containers for imple‐
165 mentations of cryptographic algorithms, and support a reference-counted
166 mechanism to allow them to be dynamically loaded in and out of the run‐
167 ning application.
168 The cryptographic functionality that can be provided by an ENGINE
170 implementation includes the following abstractions;
171 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 Reference counting and handles
180 Due to the modular nature of the ENGINE API, pointers to ENGINEs need
182 to be treated as handles - ie. not only as pointers, but also as refer‐
183 ences to the underlying ENGINE object. Ie. one should obtain a new ref‐
184 erence when making copies of an ENGINE pointer if the copies will be
185 used (and released) independantly.
186 ENGINE objects have two levels of reference-counting to match the way
188 in which the objects are used. At the most basic level, each ENGINE
189 pointer is inherently a structural reference - a structural reference
190 is required to use the pointer value at all, as this kind of reference
191 is a guarantee that the structure can not be deallocated until the ref‐
192 erence is released.
193 However, a structural reference provides no guarantee that the ENGINE
195 is initiliased and able to use any of its cryptographic implementa‐
196 tions. Indeed it's quite possible that most ENGINEs will not initialise
197 at all in typical environments, as ENGINEs are typically used to sup‐
198 port specialised hardware. To use an ENGINE's functionality, you need a
199 functional reference. This kind of reference can be considered a spe‐
200 cialised form of structural reference, because each functional refer‐
201 ence implicitly contains a structural reference as well - however to
202 avoid difficult-to-find programming bugs, it is recommended to treat
203 the two kinds of reference independantly. If you have a functional ref‐
204 erence to an ENGINE, you have a guarantee that the ENGINE has been ini‐
205 tialised ready to perform cryptographic operations and will remain
206 uninitialised until after you have released your reference.
207 Structural references
209 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 ref‐
213 erence is sufficient if you only need to query or manipulate the data
214 of an ENGINE implementation rather than use its functionality.
215 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 It should also be noted that many ENGINE API function calls that accept
226 a structural reference will internally obtain another reference - typi‐
227 cally 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 refer‐
231 ence internally so the caller is still responsible for freeing their
232 own reference with ENGINE_free() when they are finished with it. In a
233 similar way, some functions will automatically release the structural
234 reference passed to it if part of the function's job is to do so. Eg.
235 the ENGINE_get_next() and ENGINE_get_prev() functions are used for
236 iterating across the internal ENGINE list - they will return a new
237 structural reference to the next (or previous) ENGINE in the list or
238 NULL if at the end (or beginning) of the list, but in either case the
239 structural reference passed to the function is released on behalf of
240 the caller.
241 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 Functional references
247 As mentioned, functional references exist when the cryptographic func‐
249 tionality of an ENGINE is required to be available. A functional refer‐
250 ence can be obtained in one of two ways; from an existing structural
251 reference to the required ENGINE, or by asking OpenSSL for the default
252 operational ENGINE for a given cryptographic purpose.
253 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 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 Default implementations
272 For each supported abstraction, the ENGINE code maintains an internal
274 table of state to control which implementations are available for a
275 given abstraction and which should be used by default. These implemen‐
276 tations are registered in the tables and indexed by an 'nid' value,
277 because abstractions like EVP_CIPHER and EVP_DIGEST support many dis‐
278 tinct algorithms and modes, and ENGINEs can support arbitrarily many of
279 them. In the case of other abstractions like RSA, DSA, etc, there is
280 only one "algorithm" so all implementations implicitly register using
281 the same 'nid' index.
282 When a default ENGINE is requested for a given abstraction/algo‐
284 rithm/mode, (eg. when calling RSA_new_method(NULL)), a "get_default"
285 call will be made to the ENGINE subsystem to process the corresponding
286 state table and return a functional reference to an initialised ENGINE
287 whose implementation should be used. If no ENGINE should (or can) be
288 used, it will return NULL and the caller will operate with a NULL
289 ENGINE handle - this usually equates to using the conventional software
290 implementation. In the latter case, OpenSSL will from then on behave
291 the way it used to before the ENGINE API existed.
292 Each state table has a flag to note whether it has processed this
294 "get_default" query since the table was last modified, because to
295 process this question it must iterate across all the registered ENGINEs
296 in the table trying to initialise each of them in turn, in case one of
297 them is operational. If it returns a functional reference to an ENGINE,
298 it will also cache another reference to speed up processing future
299 queries (without needing to iterate across the table). Likewise, it
300 will cache a NULL response if no ENGINE was available so that future
301 queries won't repeat the same iteration unless the state table changes.
302 This behaviour can also be changed; if the ENGINE_TABLE_FLAG_NOINIT
303 flag is set (using ENGINE_set_table_flags()), no attempted initialisa‐
304 tions will take place, instead the only way for the state table to
305 return a non-NULL ENGINE to the "get_default" query will be if one is
306 expressly set in the table. Eg. ENGINE_set_default_RSA() does the same
307 job as ENGINE_register_RSA() except that it also sets the state table's
308 cached response for the "get_default" query. In the case of abstrac‐
309 tions like EVP_CIPHER, where implementations are indexed by 'nid',
310 these flags and cached-responses are distinct for each 'nid' value.
311 Application requirements
313 This section will explain the basic things an application programmer
315 should support to make the most useful elements of the ENGINE function‐
316 ality available to the user. The first thing to consider is whether the
317 programmer wishes to make alternative ENGINE modules available to the
318 application and user. OpenSSL maintains an internal linked list of
319 "visible" ENGINEs from which it has to operate - at start-up, this list
320 is empty and in fact if an application does not call any ENGINE API
321 calls and it uses static linking against openssl, then the resulting
322 application binary will not contain any alternative ENGINE code at all.
323 So the first consideration is whether any/all available ENGINE imple‐
324 mentations should be made visible to OpenSSL - this is controlled by
325 calling the various "load" functions, eg.
326 /* Make the "dynamic" ENGINE available */
328 void ENGINE_load_dynamic(void);
329 /* Make the CryptoSwift hardware acceleration support available */
330 void ENGINE_load_cswift(void);
331 /* Make support for nCipher's "CHIL" hardware available */
332 void ENGINE_load_chil(void);
333 ...
334 /* Make ALL ENGINE implementations bundled with OpenSSL available */
335 void ENGINE_load_builtin_engines(void);
336 Having called any of these functions, ENGINE objects would have been
338 dynamically allocated and populated with these implementations and
339 linked into OpenSSL's internal linked list. At this point it is impor‐
340 tant to mention an important API function;
341 void ENGINE_cleanup(void);
343 If no ENGINE API functions are called at all in an application, then
345 there are no inherent memory leaks to worry about from the ENGINE func‐
346 tionality, however if any ENGINEs are loaded, even if they are never
347 registered or used, it is necessary to use the ENGINE_cleanup() func‐
348 tion to correspondingly cleanup before program exit, if the caller
349 wishes to avoid memory leaks. This mechanism uses an internal callback
350 registration table so that any ENGINE API functionality that knows it
351 requires cleanup can register its cleanup details to be called during
352 ENGINE_cleanup(). This approach allows ENGINE_cleanup() to clean up
353 after any ENGINE functionality at all that your program uses, yet
354 doesn't automatically create linker dependencies to all possible ENGINE
355 functionality - only the cleanup callbacks required by the functional‐
356 ity you do use will be required by the linker.
357 The fact that ENGINEs are made visible to OpenSSL (and thus are linked
359 into the program and loaded into memory at run-time) does not mean they
360 are "registered" or called into use by OpenSSL automatically - that be‐
361 haviour is something for the application to control. Some applications
362 will want to allow the user to specify exactly which ENGINE they want
363 used if any is to be used at all. Others may prefer to load all support
364 and have OpenSSL automatically use at run-time any ENGINE that is able
365 to successfully initialise - ie. to assume that this corresponds to
366 acceleration hardware attached to the machine or some such thing. There
367 are probably numerous other ways in which applications may prefer to
368 handle things, so we will simply illustrate the consequences as they
369 apply to a couple of simple cases and leave developers to consider
370 these and the source code to openssl's builtin utilities as guides.
371 Using a specific ENGINE implementation
373 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 ver‐
376 sion of OpenSSL the application was compiled with. If it is available,
377 it should be used by default for all RSA, DSA, and symmetric cipher
378 operation, otherwise OpenSSL should use its builtin software as per
379 usual. The following code illustrates how to approach this;
380 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 Automatically using builtin ENGINE implementations
405 Here we'll assume we want to load and register all ENGINE implementa‐
407 tions bundled with OpenSSL, such that for any cryptographic algorithm
408 required by OpenSSL - if there is an ENGINE that implements it and can
409 be initialise, it should be used. The following code illustrates how
410 this can work;
411 /* 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 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 Advanced configuration support
423 There is a mechanism supported by the ENGINE framework that allows each
425 ENGINE implementation to define an arbitrary set of configuration "com‐
426 mands" and expose them to OpenSSL and any applications based on
427 OpenSSL. This mechanism is entirely based on the use of name-value
428 pairs and assumes ASCII input (no unicode or UTF for now!), so it is
429 ideal if applications want to provide a transparent way for users to
430 provide arbitrary configuration "directives" directly to such ENGINEs.
431 It is also possible for the application to dynamically interrogate the
432 loaded ENGINE implementations for the names, descriptions, and input
433 flags of their available "control commands", providing a more flexible
434 configuration scheme. However, if the user is expected to know which
435 ENGINE device he/she is using (in the case of specialised hardware,
436 this goes without saying) then applications may not need to concern
437 themselves with discovering the supported control commands and simply
438 prefer to pass settings into ENGINEs exactly as they are provided by
439 the user.
440 Before illustrating how control commands work, it is worth mentioning
442 what they are typically used for. Broadly speaking there are two uses
443 for control commands; the first is to provide the necessary details to
444 the implementation (which may know nothing at all specific to the host
445 system) so that it can be initialised for use. This could include the
446 path to any driver or config files it needs to load, required network
447 addresses, smart-card identifiers, passwords to initialise protected
448 devices, logging information, etc etc. This class of commands typically
449 needs to be passed to an ENGINE before attempting to initialise it, ie.
450 before calling ENGINE_init(). The other class of commands consist of
451 settings or operations that tweak certain behaviour or cause certain
452 operations to take place, and these commands may work either before or
453 after ENGINE_init(), or in some cases both. ENGINE implementations
454 should provide indications of this in the descriptions attached to
455 builtin control commands and/or in external product documentation.
456 Issuing control commands to an ENGINE
458 Let's illustrate by example; a function for which the caller supplies
460 the name of the ENGINE it wishes to use, a table of string-pairs for
461 use before initialisation, and another table for use after initialisa‐
462 tion. Note that the string-pairs used for control commands consist of a
463 command "name" followed by the command "parameter" - the parameter
464 could be NULL in some cases but the name can not. This function should
465 initialise the ENGINE (issuing the "pre" commands beforehand and the
466 "post" commands afterwards) and set it as the default for everything
467 except RAND and then return a boolean success or failure.
468 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 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 Discovering supported control commands
515 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() han‐
521 dler is not used for the control command. openssl/engine.h defines an
522 index, ENGINE_CMD_BASE, that all control commands implemented by
523 ENGINEs should be numbered from. Any command value lower than this sym‐
524 bol is considered a "generic" command is handled directly by the
525 OpenSSL core routines.
526 It is using these "core" control commands that one can discover the the
528 control commands implemented by a given ENGINE, specifically the com‐
529 mands;
530 #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 Whilst these commands are automatically processed by the OpenSSL frame‐
542 work 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 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 If the ENGINE's array of control commands is empty then all other com‐
564 mands will fail, otherwise; ENGINE_CTRL_GET_FIRST_CMD_TYPE returns the
565 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 bit‐
575 wise-OR'd mask of the following possible values;
576 #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 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 arbi‐
589 trary type. These commands are supported in the discovery mechanisms
590 simply to allow applications determinie if an ENGINE supports certain
591 specific commands it might want to use (eg. application "foo" might
592 query various ENGINEs to see if they implement "FOO_GET_VEN‐
593 DOR_LOGO_GIF" - and ENGINE could therefore decide whether or not to
594 support this "foo"-specific extension).
595 Future developments
597 The ENGINE API and internal architecture is currently being reviewed.
599 Slated for possible release in 0.9.8 is support for transparent loading
600 of "dynamic" ENGINEs (built as self-contained shared-libraries). This
601 would allow ENGINE implementations to be provided independantly of
602 OpenSSL libraries and/or OpenSSL-based applications, and would also
603 remove any requirement for applications to explicitly use the "dynamic"
604 ENGINE to bind to shared-library implementations.
605
607 rsa(3), dsa(3), dh(3), rand(3)
6080.9.8b 2004-06-17 engine(3)