| blob | f5ab1c3e50fd73476ec00ab7ede508d24aaaf94e |
1 =pod
3 =head1 NAME
5 engine - ENGINE cryptographic module support
7 =head1 SYNOPSIS
9 #include <openssl/engine.h>
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);
16 int ENGINE_add(ENGINE *e);
17 int ENGINE_remove(ENGINE *e);
19 ENGINE *ENGINE_by_id(const char *id);
21 int ENGINE_init(ENGINE *e);
22 int ENGINE_finish(ENGINE *e);
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);
40 void ENGINE_cleanup(void);
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);
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);
61 int ENGINE_set_default(ENGINE *e, unsigned int flags);
63 unsigned int ENGINE_get_table_flags(void);
64 void ENGINE_set_table_flags(unsigned int flags);
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);
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);
103 int ENGINE_set_ex_data(ENGINE *e, int idx, void *arg);
104 void *ENGINE_get_ex_data(const ENGINE *e, int idx);
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);
109 ENGINE *ENGINE_new(void);
110 int ENGINE_free(ENGINE *e);
111 int ENGINE_up_ref(ENGINE *e);
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);
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);
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);
160 void ENGINE_add_conf_module(void);
162 =head1 DESCRIPTION
164 These functions create, manipulate, and use cryptographic modules in the
165 form of B<ENGINE> objects. These objects act as containers for
166 implementations of cryptographic algorithms, and support a
167 reference-counted mechanism to allow them to be dynamically loaded in and
168 out of the running application.
170 The cryptographic functionality that can be provided by an B<ENGINE>
171 implementation includes the following abstractions;
173 RSA_METHOD - for providing alternative RSA implementations
174 DSA_METHOD, DH_METHOD, RAND_METHOD, ECDH_METHOD, ECDSA_METHOD,
175 STORE_METHOD - similarly for other OpenSSL APIs
176 EVP_CIPHER - potentially multiple cipher algorithms (indexed by 'nid')
177 EVP_DIGEST - potentially multiple hash algorithms (indexed by 'nid')
178 key-loading - loading public and/or private EVP_PKEY keys
180 =head2 Reference counting and handles
182 Due to the modular nature of the ENGINE API, pointers to ENGINEs need to be
183 treated as handles - ie. not only as pointers, but also as references to
184 the underlying ENGINE object. Ie. one should obtain a new reference when
185 making copies of an ENGINE pointer if the copies will be used (and
186 released) independently.
188 ENGINE objects have two levels of reference-counting to match the way in
189 which the objects are used. At the most basic level, each ENGINE pointer is
190 inherently a B<structural> reference - a structural reference is required
191 to use the pointer value at all, as this kind of reference is a guarantee
192 that the structure can not be deallocated until the reference is released.
194 However, a structural reference provides no guarantee that the ENGINE is
195 initiliased and able to use any of its cryptographic
196 implementations. Indeed it's quite possible that most ENGINEs will not
197 initialise at all in typical environments, as ENGINEs are typically used to
198 support specialised hardware. To use an ENGINE's functionality, you need a
199 B<functional> reference. This kind of reference can be considered a
200 specialised form of structural reference, because each functional reference
201 implicitly contains a structural reference as well - however to avoid
202 difficult-to-find programming bugs, it is recommended to treat the two
203 kinds of reference independently. If you have a functional reference to an
204 ENGINE, you have a guarantee that the ENGINE has been initialised ready to
205 perform cryptographic operations and will remain uninitialised
206 until after you have released your reference.
208 I<Structural references>
210 This basic type of reference is used for instantiating new ENGINEs,
211 iterating across OpenSSL's internal linked-list of loaded
212 ENGINEs, reading information about an ENGINE, etc. Essentially a structural
213 reference is sufficient if you only need to query or manipulate the data of
214 an ENGINE implementation rather than use its functionality.
216 The ENGINE_new() function returns a structural reference to a new (empty)
217 ENGINE object. There are other ENGINE API functions that return structural
218 references such as; ENGINE_by_id(), ENGINE_get_first(), ENGINE_get_last(),
219 ENGINE_get_next(), ENGINE_get_prev(). All structural references should be
220 released by a corresponding to call to the ENGINE_free() function - the
221 ENGINE object itself will only actually be cleaned up and deallocated when
222 the last structural reference is released.
224 It should also be noted that many ENGINE API function calls that accept a
225 structural reference will internally obtain another reference - typically
226 this happens whenever the supplied ENGINE will be needed by OpenSSL after
227 the function has returned. Eg. the function to add a new ENGINE to
228 OpenSSL's internal list is ENGINE_add() - if this function returns success,
229 then OpenSSL will have stored a new structural reference internally so the
230 caller is still responsible for freeing their own reference with
231 ENGINE_free() when they are finished with it. In a similar way, some
232 functions will automatically release the structural reference passed to it
233 if part of the function's job is to do so. Eg. the ENGINE_get_next() and
234 ENGINE_get_prev() functions are used for iterating across the internal
235 ENGINE list - they will return a new structural reference to the next (or
236 previous) ENGINE in the list or NULL if at the end (or beginning) of the
237 list, but in either case the structural reference passed to the function is
238 released on behalf of the caller.
240 To clarify a particular function's handling of references, one should
241 always consult that function's documentation "man" page, or failing that
242 the openssl/engine.h header file includes some hints.
244 I<Functional references>
246 As mentioned, functional references exist when the cryptographic
247 functionality of an ENGINE is required to be available. A functional
248 reference can be obtained in one of two ways; from an existing structural
249 reference to the required ENGINE, or by asking OpenSSL for the default
250 operational ENGINE for a given cryptographic purpose.
252 To obtain a functional reference from an existing structural reference,
253 call the ENGINE_init() function. This returns zero if the ENGINE was not
254 already operational and couldn't be successfully initialised (eg. lack of
255 system drivers, no special hardware attached, etc), otherwise it will
256 return non-zero to indicate that the ENGINE is now operational and will
257 have allocated a new B<functional> reference to the ENGINE. All functional
258 references are released by calling ENGINE_finish() (which removes the
259 implicit structural reference as well).
261 The second way to get a functional reference is by asking OpenSSL for a
262 default implementation for a given task, eg. by ENGINE_get_default_RSA(),
263 ENGINE_get_default_cipher_engine(), etc. These are discussed in the next
264 section, though they are not usually required by application programmers as
265 they are used automatically when creating and using the relevant
266 algorithm-specific types in OpenSSL, such as RSA, DSA, EVP_CIPHER_CTX, etc.
268 =head2 Default implementations
270 For each supported abstraction, the ENGINE code maintains an internal table
271 of state to control which implementations are available for a given
272 abstraction and which should be used by default. These implementations are
273 registered in the tables and indexed by an 'nid' value, because
274 abstractions like EVP_CIPHER and EVP_DIGEST support many distinct
275 algorithms and modes, and ENGINEs can support arbitrarily many of them.
276 In the case of other abstractions like RSA, DSA, etc, there is only one
277 "algorithm" so all implementations implicitly register using the same 'nid'
278 index.
280 When a default ENGINE is requested for a given abstraction/algorithm/mode, (eg.
281 when calling RSA_new_method(NULL)), a "get_default" call will be made to the
282 ENGINE subsystem to process the corresponding state table and return a
283 functional reference to an initialised ENGINE whose implementation should be
284 used. If no ENGINE should (or can) be used, it will return NULL and the caller
285 will operate with a NULL ENGINE handle - this usually equates to using the
286 conventional software implementation. In the latter case, OpenSSL will from
287 then on behave the way it used to before the ENGINE API existed.
289 Each state table has a flag to note whether it has processed this
290 "get_default" query since the table was last modified, because to process
291 this question it must iterate across all the registered ENGINEs in the
292 table trying to initialise each of them in turn, in case one of them is
293 operational. If it returns a functional reference to an ENGINE, it will
294 also cache another reference to speed up processing future queries (without
295 needing to iterate across the table). Likewise, it will cache a NULL
296 response if no ENGINE was available so that future queries won't repeat the
297 same iteration unless the state table changes. This behaviour can also be
298 changed; if the ENGINE_TABLE_FLAG_NOINIT flag is set (using
299 ENGINE_set_table_flags()), no attempted initialisations will take place,
300 instead the only way for the state table to return a non-NULL ENGINE to the
301 "get_default" query will be if one is expressly set in the table. Eg.
302 ENGINE_set_default_RSA() does the same job as ENGINE_register_RSA() except
303 that it also sets the state table's cached response for the "get_default"
304 query. In the case of abstractions like EVP_CIPHER, where implementations are
305 indexed by 'nid', these flags and cached-responses are distinct for each 'nid'
306 value.
308 =head2 Application requirements
310 This section will explain the basic things an application programmer should
311 support to make the most useful elements of the ENGINE functionality
312 available to the user. The first thing to consider is whether the
313 programmer wishes to make alternative ENGINE modules available to the
314 application and user. OpenSSL maintains an internal linked list of
315 "visible" ENGINEs from which it has to operate - at start-up, this list is
316 empty and in fact if an application does not call any ENGINE API calls and
317 it uses static linking against openssl, then the resulting application
318 binary will not contain any alternative ENGINE code at all. So the first
319 consideration is whether any/all available ENGINE implementations should be
320 made visible to OpenSSL - this is controlled by calling the various "load"
321 functions, eg.
323 /* Make the "dynamic" ENGINE available */
324 void ENGINE_load_dynamic(void);
325 /* Make the CryptoSwift hardware acceleration support available */
326 void ENGINE_load_cswift(void);
327 /* Make support for nCipher's "CHIL" hardware available */
328 void ENGINE_load_chil(void);
329 ...
330 /* Make ALL ENGINE implementations bundled with OpenSSL available */
331 void ENGINE_load_builtin_engines(void);
333 Having called any of these functions, ENGINE objects would have been
334 dynamically allocated and populated with these implementations and linked
335 into OpenSSL's internal linked list. At this point it is important to
336 mention an important API function;
338 void ENGINE_cleanup(void);
340 If no ENGINE API functions are called at all in an application, then there
341 are no inherent memory leaks to worry about from the ENGINE functionality,
342 however if any ENGINEs are loaded, even if they are never registered or
343 used, it is necessary to use the ENGINE_cleanup() function to
344 correspondingly cleanup before program exit, if the caller wishes to avoid
345 memory leaks. This mechanism uses an internal callback registration table
346 so that any ENGINE API functionality that knows it requires cleanup can
347 register its cleanup details to be called during ENGINE_cleanup(). This
348 approach allows ENGINE_cleanup() to clean up after any ENGINE functionality
349 at all that your program uses, yet doesn't automatically create linker
350 dependencies to all possible ENGINE functionality - only the cleanup
351 callbacks required by the functionality you do use will be required by the
352 linker.
354 The fact that ENGINEs are made visible to OpenSSL (and thus are linked into
355 the program and loaded into memory at run-time) does not mean they are
356 "registered" or called into use by OpenSSL automatically - that behaviour
357 is something for the application to control. Some applications
358 will want to allow the user to specify exactly which ENGINE they want used
359 if any is to be used at all. Others may prefer to load all support and have
360 OpenSSL automatically use at run-time any ENGINE that is able to
361 successfully initialise - ie. to assume that this corresponds to
362 acceleration hardware attached to the machine or some such thing. There are
363 probably numerous other ways in which applications may prefer to handle
364 things, so we will simply illustrate the consequences as they apply to a
365 couple of simple cases and leave developers to consider these and the
366 source code to openssl's builtin utilities as guides.
368 I<Using a specific ENGINE implementation>
370 Here we'll assume an application has been configured by its user or admin
371 to want to use the "ACME" ENGINE if it is available in the version of
372 OpenSSL the application was compiled with. If it is available, it should be
373 used by default for all RSA, DSA, and symmetric cipher operation, otherwise
374 OpenSSL should use its builtin software as per usual. The following code
375 illustrates how to approach this;
377 ENGINE *e;
378 const char *engine_id = "ACME";
379 ENGINE_load_builtin_engines();
380 e = ENGINE_by_id(engine_id);
381 if(!e)
382 /* the engine isn't available */
383 return;
384 if(!ENGINE_init(e)) {
385 /* the engine couldn't initialise, release 'e' */
386 ENGINE_free(e);
387 return;
388 }
389 if(!ENGINE_set_default_RSA(e))
390 /* This should only happen when 'e' can't initialise, but the previous
391 * statement suggests it did. */
392 abort();
393 ENGINE_set_default_DSA(e);
394 ENGINE_set_default_ciphers(e);
395 /* Release the functional reference from ENGINE_init() */
396 ENGINE_finish(e);
397 /* Release the structural reference from ENGINE_by_id() */
398 ENGINE_free(e);
400 I<Automatically using builtin ENGINE implementations>
402 Here we'll assume we want to load and register all ENGINE implementations
403 bundled with OpenSSL, such that for any cryptographic algorithm required by
404 OpenSSL - if there is an ENGINE that implements it and can be initialise,
405 it should be used. The following code illustrates how this can work;
407 /* Load all bundled ENGINEs into memory and make them visible */
408 ENGINE_load_builtin_engines();
409 /* Register all of them for every algorithm they collectively implement */
410 ENGINE_register_all_complete();
412 That's all that's required. Eg. the next time OpenSSL tries to set up an
413 RSA key, any bundled ENGINEs that implement RSA_METHOD will be passed to
414 ENGINE_init() and if any of those succeed, that ENGINE will be set as the
415 default for RSA use from then on.
417 =head2 Advanced configuration support
419 There is a mechanism supported by the ENGINE framework that allows each
420 ENGINE implementation to define an arbitrary set of configuration
421 "commands" and expose them to OpenSSL and any applications based on
422 OpenSSL. This mechanism is entirely based on the use of name-value pairs
423 and assumes ASCII input (no unicode or UTF for now!), so it is ideal if
424 applications want to provide a transparent way for users to provide
425 arbitrary configuration "directives" directly to such ENGINEs. It is also
426 possible for the application to dynamically interrogate the loaded ENGINE
427 implementations for the names, descriptions, and input flags of their
428 available "control commands", providing a more flexible configuration
429 scheme. However, if the user is expected to know which ENGINE device he/she
430 is using (in the case of specialised hardware, this goes without saying)
431 then applications may not need to concern themselves with discovering the
432 supported control commands and simply prefer to pass settings into ENGINEs
433 exactly as they are provided by the user.
435 Before illustrating how control commands work, it is worth mentioning what
436 they are typically used for. Broadly speaking there are two uses for
437 control commands; the first is to provide the necessary details to the
438 implementation (which may know nothing at all specific to the host system)
439 so that it can be initialised for use. This could include the path to any
440 driver or config files it needs to load, required network addresses,
441 smart-card identifiers, passwords to initialise protected devices,
442 logging information, etc etc. This class of commands typically needs to be
443 passed to an ENGINE B<before> attempting to initialise it, ie. before
444 calling ENGINE_init(). The other class of commands consist of settings or
445 operations that tweak certain behaviour or cause certain operations to take
446 place, and these commands may work either before or after ENGINE_init(), or
447 in some cases both. ENGINE implementations should provide indications of
448 this in the descriptions attached to builtin control commands and/or in
449 external product documentation.
451 I<Issuing control commands to an ENGINE>
453 Let's illustrate by example; a function for which the caller supplies the
454 name of the ENGINE it wishes to use, a table of string-pairs for use before
455 initialisation, and another table for use after initialisation. Note that
456 the string-pairs used for control commands consist of a command "name"
457 followed by the command "parameter" - the parameter could be NULL in some
458 cases but the name can not. This function should initialise the ENGINE
459 (issuing the "pre" commands beforehand and the "post" commands afterwards)
460 and set it as the default for everything except RAND and then return a
461 boolean success or failure.
463 int generic_load_engine_fn(const char *engine_id,
464 const char **pre_cmds, int pre_num,
465 const char **post_cmds, int post_num)
466 {
467 ENGINE *e = ENGINE_by_id(engine_id);
468 if(!e) return 0;
469 while(pre_num--) {
470 if(!ENGINE_ctrl_cmd_string(e, pre_cmds[0], pre_cmds[1], 0)) {
471 fprintf(stderr, "Failed command (%s - %s:%s)\n", engine_id,
472 pre_cmds[0], pre_cmds[1] ? pre_cmds[1] : "(NULL)");
473 ENGINE_free(e);
474 return 0;
475 }
476 pre_cmds += 2;
477 }
478 if(!ENGINE_init(e)) {
479 fprintf(stderr, "Failed initialisation\n");
480 ENGINE_free(e);
481 return 0;
482 }
483 /* ENGINE_init() returned a functional reference, so free the structural
484 * reference from ENGINE_by_id(). */
485 ENGINE_free(e);
486 while(post_num--) {
487 if(!ENGINE_ctrl_cmd_string(e, post_cmds[0], post_cmds[1], 0)) {
488 fprintf(stderr, "Failed command (%s - %s:%s)\n", engine_id,
489 post_cmds[0], post_cmds[1] ? post_cmds[1] : "(NULL)");
490 ENGINE_finish(e);
491 return 0;
492 }
493 post_cmds += 2;
494 }
495 ENGINE_set_default(e, ENGINE_METHOD_ALL & ~ENGINE_METHOD_RAND);
496 /* Success */
497 return 1;
498 }
500 Note that ENGINE_ctrl_cmd_string() accepts a boolean argument that can
501 relax the semantics of the function - if set non-zero it will only return
502 failure if the ENGINE supported the given command name but failed while
503 executing it, if the ENGINE doesn't support the command name it will simply
504 return success without doing anything. In this case we assume the user is
505 only supplying commands specific to the given ENGINE so we set this to
506 FALSE.
508 I<Discovering supported control commands>
510 It is possible to discover at run-time the names, numerical-ids, descriptions
511 and input parameters of the control commands supported by an ENGINE using a
512 structural reference. Note that some control commands are defined by OpenSSL
513 itself and it will intercept and handle these control commands on behalf of the
514 ENGINE, ie. the ENGINE's ctrl() handler is not used for the control command.
515 openssl/engine.h defines an index, ENGINE_CMD_BASE, that all control commands
516 implemented by ENGINEs should be numbered from. Any command value lower than
517 this symbol is considered a "generic" command is handled directly by the
518 OpenSSL core routines.
520 It is using these "core" control commands that one can discover the the control
521 commands implemented by a given ENGINE, specifically the commands;
523 #define ENGINE_HAS_CTRL_FUNCTION 10
524 #define ENGINE_CTRL_GET_FIRST_CMD_TYPE 11
525 #define ENGINE_CTRL_GET_NEXT_CMD_TYPE 12
526 #define ENGINE_CTRL_GET_CMD_FROM_NAME 13
527 #define ENGINE_CTRL_GET_NAME_LEN_FROM_CMD 14
528 #define ENGINE_CTRL_GET_NAME_FROM_CMD 15
529 #define ENGINE_CTRL_GET_DESC_LEN_FROM_CMD 16
530 #define ENGINE_CTRL_GET_DESC_FROM_CMD 17
531 #define ENGINE_CTRL_GET_CMD_FLAGS 18
533 Whilst these commands are automatically processed by the OpenSSL framework code,
534 they use various properties exposed by each ENGINE to process these
535 queries. An ENGINE has 3 properties it exposes that can affect how this behaves;
536 it can supply a ctrl() handler, it can specify ENGINE_FLAGS_MANUAL_CMD_CTRL in
537 the ENGINE's flags, and it can expose an array of control command descriptions.
538 If an ENGINE specifies the ENGINE_FLAGS_MANUAL_CMD_CTRL flag, then it will
539 simply pass all these "core" control commands directly to the ENGINE's ctrl()
540 handler (and thus, it must have supplied one), so it is up to the ENGINE to
541 reply to these "discovery" commands itself. If that flag is not set, then the
542 OpenSSL framework code will work with the following rules;
544 if no ctrl() handler supplied;
545 ENGINE_HAS_CTRL_FUNCTION returns FALSE (zero),
546 all other commands fail.
547 if a ctrl() handler was supplied but no array of control commands;
548 ENGINE_HAS_CTRL_FUNCTION returns TRUE,
549 all other commands fail.
550 if a ctrl() handler and array of control commands was supplied;
551 ENGINE_HAS_CTRL_FUNCTION returns TRUE,
552 all other commands proceed processing ...
554 If the ENGINE's array of control commands is empty then all other commands will
555 fail, otherwise; ENGINE_CTRL_GET_FIRST_CMD_TYPE returns the identifier of
556 the first command supported by the ENGINE, ENGINE_GET_NEXT_CMD_TYPE takes the
557 identifier of a command supported by the ENGINE and returns the next command
558 identifier or fails if there are no more, ENGINE_CMD_FROM_NAME takes a string
559 name for a command and returns the corresponding identifier or fails if no such
560 command name exists, and the remaining commands take a command identifier and
561 return properties of the corresponding commands. All except
562 ENGINE_CTRL_GET_FLAGS return the string length of a command name or description,
563 or populate a supplied character buffer with a copy of the command name or
564 description. ENGINE_CTRL_GET_FLAGS returns a bitwise-OR'd mask of the following
565 possible values;
567 #define ENGINE_CMD_FLAG_NUMERIC (unsigned int)0x0001
568 #define ENGINE_CMD_FLAG_STRING (unsigned int)0x0002
569 #define ENGINE_CMD_FLAG_NO_INPUT (unsigned int)0x0004
570 #define ENGINE_CMD_FLAG_INTERNAL (unsigned int)0x0008
572 If the ENGINE_CMD_FLAG_INTERNAL flag is set, then any other flags are purely
573 informational to the caller - this flag will prevent the command being usable
574 for any higher-level ENGINE functions such as ENGINE_ctrl_cmd_string().
575 "INTERNAL" commands are not intended to be exposed to text-based configuration
576 by applications, administrations, users, etc. These can support arbitrary
577 operations via ENGINE_ctrl(), including passing to and/or from the control
578 commands data of any arbitrary type. These commands are supported in the
579 discovery mechanisms simply to allow applications determinie if an ENGINE
580 supports certain specific commands it might want to use (eg. application "foo"
581 might query various ENGINEs to see if they implement "FOO_GET_VENDOR_LOGO_GIF" -
582 and ENGINE could therefore decide whether or not to support this "foo"-specific
583 extension).
585 =head2 Future developments
587 The ENGINE API and internal architecture is currently being reviewed. Slated for
588 possible release in 0.9.8 is support for transparent loading of "dynamic"
589 ENGINEs (built as self-contained shared-libraries). This would allow ENGINE
590 implementations to be provided independently of OpenSSL libraries and/or
591 OpenSSL-based applications, and would also remove any requirement for
592 applications to explicitly use the "dynamic" ENGINE to bind to shared-library
593 implementations.
595 =head1 SEE ALSO
597 L<rsa(3)|rsa(3)>, L<dsa(3)|dsa(3)>, L<dh(3)|dh(3)>, L<rand(3)|rand(3)>
599 =cut