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1 | =pod |
2 | ||
3 | =head1 NAME | |
4 | ||
5 | engine - ENGINE cryptographic module support | |
6 | ||
7 | =head1 SYNOPSIS | |
8 | ||
9 | #include <openssl/engine.h> | |
10 | ||
11 | ENGINE *ENGINE_get_first(void); | |
12 | ENGINE *ENGINE_get_last(void); | |
13 | ENGINE *ENGINE_get_next(ENGINE *e); | |
14 | ENGINE *ENGINE_get_prev(ENGINE *e); | |
15 | ||
16 | int ENGINE_add(ENGINE *e); | |
17 | int ENGINE_remove(ENGINE *e); | |
18 | ||
19 | ENGINE *ENGINE_by_id(const char *id); | |
20 | ||
21 | int ENGINE_init(ENGINE *e); | |
22 | int ENGINE_finish(ENGINE *e); | |
23 | ||
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24 | void ENGINE_load_builtin_engines(void); |
25 | ||
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26 | ENGINE *ENGINE_get_default_RSA(void); |
27 | ENGINE *ENGINE_get_default_DSA(void); | |
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28 | ENGINE *ENGINE_get_default_ECDH(void); |
29 | ENGINE *ENGINE_get_default_ECDSA(void); | |
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30 | ENGINE *ENGINE_get_default_DH(void); |
31 | ENGINE *ENGINE_get_default_RAND(void); | |
32 | ENGINE *ENGINE_get_cipher_engine(int nid); | |
33 | ENGINE *ENGINE_get_digest_engine(int nid); | |
34 | ||
35 | int ENGINE_set_default_RSA(ENGINE *e); | |
36 | int ENGINE_set_default_DSA(ENGINE *e); | |
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37 | int ENGINE_set_default_ECDH(ENGINE *e); |
38 | int ENGINE_set_default_ECDSA(ENGINE *e); | |
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39 | int ENGINE_set_default_DH(ENGINE *e); |
40 | int ENGINE_set_default_RAND(ENGINE *e); | |
41 | int ENGINE_set_default_ciphers(ENGINE *e); | |
42 | int ENGINE_set_default_digests(ENGINE *e); | |
43 | int ENGINE_set_default_string(ENGINE *e, const char *list); | |
44 | ||
45 | int ENGINE_set_default(ENGINE *e, unsigned int flags); | |
46 | ||
47 | unsigned int ENGINE_get_table_flags(void); | |
48 | void ENGINE_set_table_flags(unsigned int flags); | |
49 | ||
50 | int ENGINE_register_RSA(ENGINE *e); | |
51 | void ENGINE_unregister_RSA(ENGINE *e); | |
52 | void ENGINE_register_all_RSA(void); | |
53 | int ENGINE_register_DSA(ENGINE *e); | |
54 | void ENGINE_unregister_DSA(ENGINE *e); | |
55 | void ENGINE_register_all_DSA(void); | |
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56 | int ENGINE_register_ECDH(ENGINE *e); |
57 | void ENGINE_unregister_ECDH(ENGINE *e); | |
58 | void ENGINE_register_all_ECDH(void); | |
59 | int ENGINE_register_ECDSA(ENGINE *e); | |
60 | void ENGINE_unregister_ECDSA(ENGINE *e); | |
61 | void ENGINE_register_all_ECDSA(void); | |
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62 | int ENGINE_register_DH(ENGINE *e); |
63 | void ENGINE_unregister_DH(ENGINE *e); | |
64 | void ENGINE_register_all_DH(void); | |
65 | int ENGINE_register_RAND(ENGINE *e); | |
66 | void ENGINE_unregister_RAND(ENGINE *e); | |
67 | void ENGINE_register_all_RAND(void); | |
68 | int ENGINE_register_ciphers(ENGINE *e); | |
69 | void ENGINE_unregister_ciphers(ENGINE *e); | |
70 | void ENGINE_register_all_ciphers(void); | |
71 | int ENGINE_register_digests(ENGINE *e); | |
72 | void ENGINE_unregister_digests(ENGINE *e); | |
73 | void ENGINE_register_all_digests(void); | |
74 | int ENGINE_register_complete(ENGINE *e); | |
75 | int ENGINE_register_all_complete(void); | |
76 | ||
6a659296 | 77 | int ENGINE_ctrl(ENGINE *e, int cmd, long i, void *p, void (*f)(void)); |
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78 | int ENGINE_cmd_is_executable(ENGINE *e, int cmd); |
79 | int ENGINE_ctrl_cmd(ENGINE *e, const char *cmd_name, | |
6a659296 | 80 | long i, void *p, void (*f)(void), int cmd_optional); |
3f90e450 | 81 | int ENGINE_ctrl_cmd_string(ENGINE *e, const char *cmd_name, const char *arg, |
6a659296 | 82 | int cmd_optional); |
3f90e450 | 83 | |
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84 | ENGINE *ENGINE_new(void); |
85 | int ENGINE_free(ENGINE *e); | |
6a659296 | 86 | int ENGINE_up_ref(ENGINE *e); |
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87 | |
88 | int ENGINE_set_id(ENGINE *e, const char *id); | |
89 | int ENGINE_set_name(ENGINE *e, const char *name); | |
90 | int ENGINE_set_RSA(ENGINE *e, const RSA_METHOD *rsa_meth); | |
91 | int ENGINE_set_DSA(ENGINE *e, const DSA_METHOD *dsa_meth); | |
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92 | int ENGINE_set_ECDH(ENGINE *e, const ECDH_METHOD *dh_meth); |
93 | int ENGINE_set_ECDSA(ENGINE *e, const ECDSA_METHOD *dh_meth); | |
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94 | int ENGINE_set_DH(ENGINE *e, const DH_METHOD *dh_meth); |
95 | int ENGINE_set_RAND(ENGINE *e, const RAND_METHOD *rand_meth); | |
96 | int ENGINE_set_destroy_function(ENGINE *e, ENGINE_GEN_INT_FUNC_PTR destroy_f); | |
97 | int ENGINE_set_init_function(ENGINE *e, ENGINE_GEN_INT_FUNC_PTR init_f); | |
98 | int ENGINE_set_finish_function(ENGINE *e, ENGINE_GEN_INT_FUNC_PTR finish_f); | |
99 | int ENGINE_set_ctrl_function(ENGINE *e, ENGINE_CTRL_FUNC_PTR ctrl_f); | |
100 | int ENGINE_set_load_privkey_function(ENGINE *e, ENGINE_LOAD_KEY_PTR loadpriv_f); | |
101 | int ENGINE_set_load_pubkey_function(ENGINE *e, ENGINE_LOAD_KEY_PTR loadpub_f); | |
102 | int ENGINE_set_ciphers(ENGINE *e, ENGINE_CIPHERS_PTR f); | |
103 | int ENGINE_set_digests(ENGINE *e, ENGINE_DIGESTS_PTR f); | |
104 | int ENGINE_set_flags(ENGINE *e, int flags); | |
105 | int ENGINE_set_cmd_defns(ENGINE *e, const ENGINE_CMD_DEFN *defns); | |
106 | ||
107 | const char *ENGINE_get_id(const ENGINE *e); | |
108 | const char *ENGINE_get_name(const ENGINE *e); | |
109 | const RSA_METHOD *ENGINE_get_RSA(const ENGINE *e); | |
110 | const DSA_METHOD *ENGINE_get_DSA(const ENGINE *e); | |
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111 | const ECDH_METHOD *ENGINE_get_ECDH(const ENGINE *e); |
112 | const ECDSA_METHOD *ENGINE_get_ECDSA(const ENGINE *e); | |
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113 | const DH_METHOD *ENGINE_get_DH(const ENGINE *e); |
114 | const RAND_METHOD *ENGINE_get_RAND(const ENGINE *e); | |
115 | ENGINE_GEN_INT_FUNC_PTR ENGINE_get_destroy_function(const ENGINE *e); | |
116 | ENGINE_GEN_INT_FUNC_PTR ENGINE_get_init_function(const ENGINE *e); | |
117 | ENGINE_GEN_INT_FUNC_PTR ENGINE_get_finish_function(const ENGINE *e); | |
118 | ENGINE_CTRL_FUNC_PTR ENGINE_get_ctrl_function(const ENGINE *e); | |
119 | ENGINE_LOAD_KEY_PTR ENGINE_get_load_privkey_function(const ENGINE *e); | |
120 | ENGINE_LOAD_KEY_PTR ENGINE_get_load_pubkey_function(const ENGINE *e); | |
121 | ENGINE_CIPHERS_PTR ENGINE_get_ciphers(const ENGINE *e); | |
122 | ENGINE_DIGESTS_PTR ENGINE_get_digests(const ENGINE *e); | |
123 | const EVP_CIPHER *ENGINE_get_cipher(ENGINE *e, int nid); | |
124 | const EVP_MD *ENGINE_get_digest(ENGINE *e, int nid); | |
125 | int ENGINE_get_flags(const ENGINE *e); | |
126 | const ENGINE_CMD_DEFN *ENGINE_get_cmd_defns(const ENGINE *e); | |
127 | ||
128 | EVP_PKEY *ENGINE_load_private_key(ENGINE *e, const char *key_id, | |
129 | UI_METHOD *ui_method, void *callback_data); | |
130 | EVP_PKEY *ENGINE_load_public_key(ENGINE *e, const char *key_id, | |
131 | UI_METHOD *ui_method, void *callback_data); | |
132 | ||
133 | void ENGINE_add_conf_module(void); | |
134 | ||
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135 | Deprecated: |
136 | ||
137 | #if OPENSSL_API_COMPAT < 0x10100000L | |
138 | # define ENGINE_cleanup() | |
139 | #endif | |
140 | ||
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141 | =head1 DESCRIPTION |
142 | ||
143 | These functions create, manipulate, and use cryptographic modules in the | |
144 | form of B<ENGINE> objects. These objects act as containers for | |
145 | implementations of cryptographic algorithms, and support a | |
146 | reference-counted mechanism to allow them to be dynamically loaded in and | |
147 | out of the running application. | |
148 | ||
149 | The cryptographic functionality that can be provided by an B<ENGINE> | |
150 | implementation includes the following abstractions; | |
151 | ||
152 | RSA_METHOD - for providing alternative RSA implementations | |
6a659296 | 153 | DSA_METHOD, DH_METHOD, RAND_METHOD, ECDH_METHOD, ECDSA_METHOD, |
7984f082 | 154 | - similarly for other OpenSSL APIs |
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155 | EVP_CIPHER - potentially multiple cipher algorithms (indexed by 'nid') |
156 | EVP_DIGEST - potentially multiple hash algorithms (indexed by 'nid') | |
157 | key-loading - loading public and/or private EVP_PKEY keys | |
158 | ||
159 | =head2 Reference counting and handles | |
160 | ||
161 | Due to the modular nature of the ENGINE API, pointers to ENGINEs need to be | |
162 | treated as handles - ie. not only as pointers, but also as references to | |
6a659296 | 163 | the underlying ENGINE object. Ie. one should obtain a new reference when |
3f90e450 | 164 | making copies of an ENGINE pointer if the copies will be used (and |
b6a338cb | 165 | released) independently. |
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166 | |
167 | ENGINE objects have two levels of reference-counting to match the way in | |
168 | which the objects are used. At the most basic level, each ENGINE pointer is | |
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169 | inherently a B<structural> reference - a structural reference is required |
170 | to use the pointer value at all, as this kind of reference is a guarantee | |
171 | that the structure can not be deallocated until the reference is released. | |
172 | ||
173 | However, a structural reference provides no guarantee that the ENGINE is | |
740ceb5b | 174 | initialised and able to use any of its cryptographic |
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175 | implementations. Indeed it's quite possible that most ENGINEs will not |
176 | initialise at all in typical environments, as ENGINEs are typically used to | |
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177 | support specialised hardware. To use an ENGINE's functionality, you need a |
178 | B<functional> reference. This kind of reference can be considered a | |
179 | specialised form of structural reference, because each functional reference | |
180 | implicitly contains a structural reference as well - however to avoid | |
181 | difficult-to-find programming bugs, it is recommended to treat the two | |
b6a338cb | 182 | kinds of reference independently. If you have a functional reference to an |
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183 | ENGINE, you have a guarantee that the ENGINE has been initialised and |
184 | is ready to perform cryptographic operations, and will remain initialised | |
6a659296 | 185 | until after you have released your reference. |
3f90e450 | 186 | |
4390d661 | 187 | I<Structural references> |
3f90e450 | 188 | |
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189 | This basic type of reference is used for instantiating new ENGINEs, |
190 | iterating across OpenSSL's internal linked-list of loaded | |
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191 | ENGINEs, reading information about an ENGINE, etc. Essentially a structural |
192 | reference is sufficient if you only need to query or manipulate the data of | |
193 | an ENGINE implementation rather than use its functionality. | |
194 | ||
195 | The ENGINE_new() function returns a structural reference to a new (empty) | |
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196 | ENGINE object. There are other ENGINE API functions that return structural |
197 | references such as; ENGINE_by_id(), ENGINE_get_first(), ENGINE_get_last(), | |
198 | ENGINE_get_next(), ENGINE_get_prev(). All structural references should be | |
199 | released by a corresponding to call to the ENGINE_free() function - the | |
200 | ENGINE object itself will only actually be cleaned up and deallocated when | |
201 | the last structural reference is released. | |
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202 | |
203 | It should also be noted that many ENGINE API function calls that accept a | |
204 | structural reference will internally obtain another reference - typically | |
205 | this happens whenever the supplied ENGINE will be needed by OpenSSL after | |
206 | the function has returned. Eg. the function to add a new ENGINE to | |
207 | OpenSSL's internal list is ENGINE_add() - if this function returns success, | |
208 | then OpenSSL will have stored a new structural reference internally so the | |
209 | caller is still responsible for freeing their own reference with | |
210 | ENGINE_free() when they are finished with it. In a similar way, some | |
211 | functions will automatically release the structural reference passed to it | |
212 | if part of the function's job is to do so. Eg. the ENGINE_get_next() and | |
213 | ENGINE_get_prev() functions are used for iterating across the internal | |
214 | ENGINE list - they will return a new structural reference to the next (or | |
215 | previous) ENGINE in the list or NULL if at the end (or beginning) of the | |
216 | list, but in either case the structural reference passed to the function is | |
217 | released on behalf of the caller. | |
218 | ||
219 | To clarify a particular function's handling of references, one should | |
220 | always consult that function's documentation "man" page, or failing that | |
221 | the openssl/engine.h header file includes some hints. | |
222 | ||
4390d661 | 223 | I<Functional references> |
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224 | |
225 | As mentioned, functional references exist when the cryptographic | |
226 | functionality of an ENGINE is required to be available. A functional | |
227 | reference can be obtained in one of two ways; from an existing structural | |
228 | reference to the required ENGINE, or by asking OpenSSL for the default | |
229 | operational ENGINE for a given cryptographic purpose. | |
230 | ||
231 | To obtain a functional reference from an existing structural reference, | |
232 | call the ENGINE_init() function. This returns zero if the ENGINE was not | |
233 | already operational and couldn't be successfully initialised (eg. lack of | |
234 | system drivers, no special hardware attached, etc), otherwise it will | |
235 | return non-zero to indicate that the ENGINE is now operational and will | |
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236 | have allocated a new B<functional> reference to the ENGINE. All functional |
237 | references are released by calling ENGINE_finish() (which removes the | |
238 | implicit structural reference as well). | |
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239 | |
240 | The second way to get a functional reference is by asking OpenSSL for a | |
241 | default implementation for a given task, eg. by ENGINE_get_default_RSA(), | |
242 | ENGINE_get_default_cipher_engine(), etc. These are discussed in the next | |
243 | section, though they are not usually required by application programmers as | |
244 | they are used automatically when creating and using the relevant | |
245 | algorithm-specific types in OpenSSL, such as RSA, DSA, EVP_CIPHER_CTX, etc. | |
246 | ||
247 | =head2 Default implementations | |
248 | ||
249 | For each supported abstraction, the ENGINE code maintains an internal table | |
250 | of state to control which implementations are available for a given | |
251 | abstraction and which should be used by default. These implementations are | |
6a659296 | 252 | registered in the tables and indexed by an 'nid' value, because |
3f90e450 | 253 | abstractions like EVP_CIPHER and EVP_DIGEST support many distinct |
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254 | algorithms and modes, and ENGINEs can support arbitrarily many of them. |
255 | In the case of other abstractions like RSA, DSA, etc, there is only one | |
256 | "algorithm" so all implementations implicitly register using the same 'nid' | |
257 | index. | |
258 | ||
259 | When a default ENGINE is requested for a given abstraction/algorithm/mode, (eg. | |
260 | when calling RSA_new_method(NULL)), a "get_default" call will be made to the | |
261 | ENGINE subsystem to process the corresponding state table and return a | |
262 | functional reference to an initialised ENGINE whose implementation should be | |
263 | used. If no ENGINE should (or can) be used, it will return NULL and the caller | |
264 | will operate with a NULL ENGINE handle - this usually equates to using the | |
265 | conventional software implementation. In the latter case, OpenSSL will from | |
266 | then on behave the way it used to before the ENGINE API existed. | |
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267 | |
268 | Each state table has a flag to note whether it has processed this | |
269 | "get_default" query since the table was last modified, because to process | |
270 | this question it must iterate across all the registered ENGINEs in the | |
271 | table trying to initialise each of them in turn, in case one of them is | |
272 | operational. If it returns a functional reference to an ENGINE, it will | |
273 | also cache another reference to speed up processing future queries (without | |
274 | needing to iterate across the table). Likewise, it will cache a NULL | |
275 | response if no ENGINE was available so that future queries won't repeat the | |
276 | same iteration unless the state table changes. This behaviour can also be | |
277 | changed; if the ENGINE_TABLE_FLAG_NOINIT flag is set (using | |
278 | ENGINE_set_table_flags()), no attempted initialisations will take place, | |
279 | instead the only way for the state table to return a non-NULL ENGINE to the | |
280 | "get_default" query will be if one is expressly set in the table. Eg. | |
281 | ENGINE_set_default_RSA() does the same job as ENGINE_register_RSA() except | |
282 | that it also sets the state table's cached response for the "get_default" | |
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283 | query. In the case of abstractions like EVP_CIPHER, where implementations are |
284 | indexed by 'nid', these flags and cached-responses are distinct for each 'nid' | |
285 | value. | |
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286 | |
287 | =head2 Application requirements | |
288 | ||
289 | This section will explain the basic things an application programmer should | |
290 | support to make the most useful elements of the ENGINE functionality | |
291 | available to the user. The first thing to consider is whether the | |
292 | programmer wishes to make alternative ENGINE modules available to the | |
293 | application and user. OpenSSL maintains an internal linked list of | |
294 | "visible" ENGINEs from which it has to operate - at start-up, this list is | |
295 | empty and in fact if an application does not call any ENGINE API calls and | |
296 | it uses static linking against openssl, then the resulting application | |
297 | binary will not contain any alternative ENGINE code at all. So the first | |
298 | consideration is whether any/all available ENGINE implementations should be | |
299 | made visible to OpenSSL - this is controlled by calling the various "load" | |
f672aee4 | 300 | functions. |
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301 | |
302 | Having called any of these functions, ENGINE objects would have been | |
303 | dynamically allocated and populated with these implementations and linked | |
304 | into OpenSSL's internal linked list. At this point it is important to | |
305 | mention an important API function; | |
306 | ||
6d4fb1d5 | 307 | ENGINE_cleanup() |
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308 | |
309 | If no ENGINE API functions are called at all in an application, then there | |
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310 | are no inherent memory leaks to worry about from the ENGINE functionality. |
311 | However, prior to OpenSSL 1.1.0 if any ENGINEs are loaded, even if they are | |
312 | never registered or used, it was necessary to use the ENGINE_cleanup() function | |
313 | to correspondingly cleanup before program exit, if the caller wishes to avoid | |
314 | memory leaks. This mechanism used an internal callback registration table | |
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315 | so that any ENGINE API functionality that knows it requires cleanup can |
316 | register its cleanup details to be called during ENGINE_cleanup(). This | |
6d4fb1d5 | 317 | approach allowed ENGINE_cleanup() to clean up after any ENGINE functionality |
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318 | at all that your program uses, yet doesn't automatically create linker |
319 | dependencies to all possible ENGINE functionality - only the cleanup | |
320 | callbacks required by the functionality you do use will be required by the | |
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321 | linker. From OpenSSL 1.1.0 it is no longer necessary to explicitly call |
322 | ENGINE_cleanup and this function is deprecated. Cleanup automatically takes | |
323 | place at program exit. | |
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324 | |
325 | The fact that ENGINEs are made visible to OpenSSL (and thus are linked into | |
326 | the program and loaded into memory at run-time) does not mean they are | |
327 | "registered" or called into use by OpenSSL automatically - that behaviour | |
6a659296 | 328 | is something for the application to control. Some applications |
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329 | will want to allow the user to specify exactly which ENGINE they want used |
330 | if any is to be used at all. Others may prefer to load all support and have | |
331 | OpenSSL automatically use at run-time any ENGINE that is able to | |
332 | successfully initialise - ie. to assume that this corresponds to | |
333 | acceleration hardware attached to the machine or some such thing. There are | |
334 | probably numerous other ways in which applications may prefer to handle | |
335 | things, so we will simply illustrate the consequences as they apply to a | |
336 | couple of simple cases and leave developers to consider these and the | |
337 | source code to openssl's builtin utilities as guides. | |
338 | ||
4390d661 | 339 | I<Using a specific ENGINE implementation> |
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340 | |
341 | Here we'll assume an application has been configured by its user or admin | |
342 | to want to use the "ACME" ENGINE if it is available in the version of | |
343 | OpenSSL the application was compiled with. If it is available, it should be | |
740ceb5b | 344 | used by default for all RSA, DSA, and symmetric cipher operations, otherwise |
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345 | OpenSSL should use its builtin software as per usual. The following code |
346 | illustrates how to approach this; | |
347 | ||
348 | ENGINE *e; | |
349 | const char *engine_id = "ACME"; | |
350 | ENGINE_load_builtin_engines(); | |
351 | e = ENGINE_by_id(engine_id); | |
352 | if(!e) | |
353 | /* the engine isn't available */ | |
354 | return; | |
355 | if(!ENGINE_init(e)) { | |
356 | /* the engine couldn't initialise, release 'e' */ | |
357 | ENGINE_free(e); | |
358 | return; | |
359 | } | |
360 | if(!ENGINE_set_default_RSA(e)) | |
361 | /* This should only happen when 'e' can't initialise, but the previous | |
362 | * statement suggests it did. */ | |
363 | abort(); | |
364 | ENGINE_set_default_DSA(e); | |
365 | ENGINE_set_default_ciphers(e); | |
366 | /* Release the functional reference from ENGINE_init() */ | |
367 | ENGINE_finish(e); | |
368 | /* Release the structural reference from ENGINE_by_id() */ | |
369 | ENGINE_free(e); | |
370 | ||
4390d661 | 371 | I<Automatically using builtin ENGINE implementations> |
3f90e450 GT |
372 | |
373 | Here we'll assume we want to load and register all ENGINE implementations | |
374 | bundled with OpenSSL, such that for any cryptographic algorithm required by | |
740ceb5b | 375 | OpenSSL - if there is an ENGINE that implements it and can be initialised, |
3f90e450 GT |
376 | it should be used. The following code illustrates how this can work; |
377 | ||
378 | /* Load all bundled ENGINEs into memory and make them visible */ | |
379 | ENGINE_load_builtin_engines(); | |
380 | /* Register all of them for every algorithm they collectively implement */ | |
381 | ENGINE_register_all_complete(); | |
382 | ||
383 | That's all that's required. Eg. the next time OpenSSL tries to set up an | |
384 | RSA key, any bundled ENGINEs that implement RSA_METHOD will be passed to | |
385 | ENGINE_init() and if any of those succeed, that ENGINE will be set as the | |
6a659296 | 386 | default for RSA use from then on. |
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387 | |
388 | =head2 Advanced configuration support | |
389 | ||
390 | There is a mechanism supported by the ENGINE framework that allows each | |
391 | ENGINE implementation to define an arbitrary set of configuration | |
392 | "commands" and expose them to OpenSSL and any applications based on | |
393 | OpenSSL. This mechanism is entirely based on the use of name-value pairs | |
6a659296 | 394 | and assumes ASCII input (no unicode or UTF for now!), so it is ideal if |
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395 | applications want to provide a transparent way for users to provide |
396 | arbitrary configuration "directives" directly to such ENGINEs. It is also | |
397 | possible for the application to dynamically interrogate the loaded ENGINE | |
398 | implementations for the names, descriptions, and input flags of their | |
399 | available "control commands", providing a more flexible configuration | |
400 | scheme. However, if the user is expected to know which ENGINE device he/she | |
401 | is using (in the case of specialised hardware, this goes without saying) | |
402 | then applications may not need to concern themselves with discovering the | |
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403 | supported control commands and simply prefer to pass settings into ENGINEs |
404 | exactly as they are provided by the user. | |
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405 | |
406 | Before illustrating how control commands work, it is worth mentioning what | |
407 | they are typically used for. Broadly speaking there are two uses for | |
408 | control commands; the first is to provide the necessary details to the | |
409 | implementation (which may know nothing at all specific to the host system) | |
410 | so that it can be initialised for use. This could include the path to any | |
411 | driver or config files it needs to load, required network addresses, | |
6a659296 | 412 | smart-card identifiers, passwords to initialise protected devices, |
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413 | logging information, etc etc. This class of commands typically needs to be |
414 | passed to an ENGINE B<before> attempting to initialise it, ie. before | |
415 | calling ENGINE_init(). The other class of commands consist of settings or | |
416 | operations that tweak certain behaviour or cause certain operations to take | |
417 | place, and these commands may work either before or after ENGINE_init(), or | |
6a659296 | 418 | in some cases both. ENGINE implementations should provide indications of |
3f90e450 GT |
419 | this in the descriptions attached to builtin control commands and/or in |
420 | external product documentation. | |
421 | ||
4390d661 | 422 | I<Issuing control commands to an ENGINE> |
3f90e450 GT |
423 | |
424 | Let's illustrate by example; a function for which the caller supplies the | |
425 | name of the ENGINE it wishes to use, a table of string-pairs for use before | |
426 | initialisation, and another table for use after initialisation. Note that | |
427 | the string-pairs used for control commands consist of a command "name" | |
428 | followed by the command "parameter" - the parameter could be NULL in some | |
429 | cases but the name can not. This function should initialise the ENGINE | |
430 | (issuing the "pre" commands beforehand and the "post" commands afterwards) | |
431 | and set it as the default for everything except RAND and then return a | |
432 | boolean success or failure. | |
433 | ||
434 | int generic_load_engine_fn(const char *engine_id, | |
435 | const char **pre_cmds, int pre_num, | |
436 | const char **post_cmds, int post_num) | |
437 | { | |
438 | ENGINE *e = ENGINE_by_id(engine_id); | |
439 | if(!e) return 0; | |
440 | while(pre_num--) { | |
441 | if(!ENGINE_ctrl_cmd_string(e, pre_cmds[0], pre_cmds[1], 0)) { | |
442 | fprintf(stderr, "Failed command (%s - %s:%s)\n", engine_id, | |
443 | pre_cmds[0], pre_cmds[1] ? pre_cmds[1] : "(NULL)"); | |
444 | ENGINE_free(e); | |
445 | return 0; | |
446 | } | |
447 | pre_cmds += 2; | |
448 | } | |
449 | if(!ENGINE_init(e)) { | |
450 | fprintf(stderr, "Failed initialisation\n"); | |
451 | ENGINE_free(e); | |
452 | return 0; | |
453 | } | |
454 | /* ENGINE_init() returned a functional reference, so free the structural | |
455 | * reference from ENGINE_by_id(). */ | |
456 | ENGINE_free(e); | |
457 | while(post_num--) { | |
458 | if(!ENGINE_ctrl_cmd_string(e, post_cmds[0], post_cmds[1], 0)) { | |
459 | fprintf(stderr, "Failed command (%s - %s:%s)\n", engine_id, | |
460 | post_cmds[0], post_cmds[1] ? post_cmds[1] : "(NULL)"); | |
461 | ENGINE_finish(e); | |
462 | return 0; | |
463 | } | |
464 | post_cmds += 2; | |
465 | } | |
466 | ENGINE_set_default(e, ENGINE_METHOD_ALL & ~ENGINE_METHOD_RAND); | |
467 | /* Success */ | |
468 | return 1; | |
469 | } | |
470 | ||
471 | Note that ENGINE_ctrl_cmd_string() accepts a boolean argument that can | |
472 | relax the semantics of the function - if set non-zero it will only return | |
473 | failure if the ENGINE supported the given command name but failed while | |
474 | executing it, if the ENGINE doesn't support the command name it will simply | |
475 | return success without doing anything. In this case we assume the user is | |
476 | only supplying commands specific to the given ENGINE so we set this to | |
477 | FALSE. | |
478 | ||
4390d661 | 479 | I<Discovering supported control commands> |
3f90e450 GT |
480 | |
481 | It is possible to discover at run-time the names, numerical-ids, descriptions | |
6a659296 GT |
482 | and input parameters of the control commands supported by an ENGINE using a |
483 | structural reference. Note that some control commands are defined by OpenSSL | |
484 | itself and it will intercept and handle these control commands on behalf of the | |
485 | ENGINE, ie. the ENGINE's ctrl() handler is not used for the control command. | |
486 | openssl/engine.h defines an index, ENGINE_CMD_BASE, that all control commands | |
487 | implemented by ENGINEs should be numbered from. Any command value lower than | |
488 | this symbol is considered a "generic" command is handled directly by the | |
489 | OpenSSL core routines. | |
3f90e450 | 490 | |
b9b6a7e5 | 491 | It is using these "core" control commands that one can discover the control |
3f90e450 GT |
492 | commands implemented by a given ENGINE, specifically the commands; |
493 | ||
494 | #define ENGINE_HAS_CTRL_FUNCTION 10 | |
495 | #define ENGINE_CTRL_GET_FIRST_CMD_TYPE 11 | |
496 | #define ENGINE_CTRL_GET_NEXT_CMD_TYPE 12 | |
497 | #define ENGINE_CTRL_GET_CMD_FROM_NAME 13 | |
498 | #define ENGINE_CTRL_GET_NAME_LEN_FROM_CMD 14 | |
499 | #define ENGINE_CTRL_GET_NAME_FROM_CMD 15 | |
500 | #define ENGINE_CTRL_GET_DESC_LEN_FROM_CMD 16 | |
501 | #define ENGINE_CTRL_GET_DESC_FROM_CMD 17 | |
502 | #define ENGINE_CTRL_GET_CMD_FLAGS 18 | |
503 | ||
504 | Whilst these commands are automatically processed by the OpenSSL framework code, | |
6a659296 GT |
505 | they use various properties exposed by each ENGINE to process these |
506 | queries. An ENGINE has 3 properties it exposes that can affect how this behaves; | |
3f90e450 GT |
507 | it can supply a ctrl() handler, it can specify ENGINE_FLAGS_MANUAL_CMD_CTRL in |
508 | the ENGINE's flags, and it can expose an array of control command descriptions. | |
509 | If an ENGINE specifies the ENGINE_FLAGS_MANUAL_CMD_CTRL flag, then it will | |
510 | simply pass all these "core" control commands directly to the ENGINE's ctrl() | |
511 | handler (and thus, it must have supplied one), so it is up to the ENGINE to | |
512 | reply to these "discovery" commands itself. If that flag is not set, then the | |
513 | OpenSSL framework code will work with the following rules; | |
514 | ||
515 | if no ctrl() handler supplied; | |
516 | ENGINE_HAS_CTRL_FUNCTION returns FALSE (zero), | |
517 | all other commands fail. | |
518 | if a ctrl() handler was supplied but no array of control commands; | |
519 | ENGINE_HAS_CTRL_FUNCTION returns TRUE, | |
520 | all other commands fail. | |
521 | if a ctrl() handler and array of control commands was supplied; | |
522 | ENGINE_HAS_CTRL_FUNCTION returns TRUE, | |
523 | all other commands proceed processing ... | |
524 | ||
525 | If the ENGINE's array of control commands is empty then all other commands will | |
526 | fail, otherwise; ENGINE_CTRL_GET_FIRST_CMD_TYPE returns the identifier of | |
527 | the first command supported by the ENGINE, ENGINE_GET_NEXT_CMD_TYPE takes the | |
528 | identifier of a command supported by the ENGINE and returns the next command | |
529 | identifier or fails if there are no more, ENGINE_CMD_FROM_NAME takes a string | |
530 | name for a command and returns the corresponding identifier or fails if no such | |
531 | command name exists, and the remaining commands take a command identifier and | |
532 | return properties of the corresponding commands. All except | |
533 | ENGINE_CTRL_GET_FLAGS return the string length of a command name or description, | |
534 | or populate a supplied character buffer with a copy of the command name or | |
535 | description. ENGINE_CTRL_GET_FLAGS returns a bitwise-OR'd mask of the following | |
536 | possible values; | |
537 | ||
538 | #define ENGINE_CMD_FLAG_NUMERIC (unsigned int)0x0001 | |
539 | #define ENGINE_CMD_FLAG_STRING (unsigned int)0x0002 | |
540 | #define ENGINE_CMD_FLAG_NO_INPUT (unsigned int)0x0004 | |
541 | #define ENGINE_CMD_FLAG_INTERNAL (unsigned int)0x0008 | |
542 | ||
543 | If the ENGINE_CMD_FLAG_INTERNAL flag is set, then any other flags are purely | |
544 | informational to the caller - this flag will prevent the command being usable | |
545 | for any higher-level ENGINE functions such as ENGINE_ctrl_cmd_string(). | |
546 | "INTERNAL" commands are not intended to be exposed to text-based configuration | |
547 | by applications, administrations, users, etc. These can support arbitrary | |
548 | operations via ENGINE_ctrl(), including passing to and/or from the control | |
549 | commands data of any arbitrary type. These commands are supported in the | |
186bb907 | 550 | discovery mechanisms simply to allow applications to determine if an ENGINE |
3f90e450 GT |
551 | supports certain specific commands it might want to use (eg. application "foo" |
552 | might query various ENGINEs to see if they implement "FOO_GET_VENDOR_LOGO_GIF" - | |
553 | and ENGINE could therefore decide whether or not to support this "foo"-specific | |
554 | extension). | |
555 | ||
3f90e450 GT |
556 | =head1 SEE ALSO |
557 | ||
f672aee4 RS |
558 | L<OPENSSL_init_crypto(3)>, L<rsa(3)>, L<dsa(3)>, L<dh(3)>, L<rand(3)> |
559 | ||
560 | =head1 HISTORY | |
561 | ||
6d4fb1d5 MC |
562 | ENGINE_cleanup(), ENGINE_load_openssl(), ENGINE_load_dynamic(), and |
563 | ENGINE_load_cryptodev() were deprecated in OpenSSL 1.1.0 by | |
564 | OPENSSL_init_crypto(). | |
3f90e450 GT |
565 | |
566 | =cut |