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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 | ||
24 | void ENGINE_load_openssl(void); | |
25 | void ENGINE_load_dynamic(void); | |
6a659296 | 26 | #ifndef OPENSSL_NO_STATIC_ENGINE |
6a659296 | 27 | void ENGINE_load_chil(void); |
6a659296 | 28 | void ENGINE_load_gmp(void); |
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29 | void ENGINE_load_ubsec(void); |
30 | #endif | |
31 | void ENGINE_load_cryptodev(void); | |
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32 | void ENGINE_load_builtin_engines(void); |
33 | ||
34 | void ENGINE_cleanup(void); | |
35 | ||
36 | ENGINE *ENGINE_get_default_RSA(void); | |
37 | ENGINE *ENGINE_get_default_DSA(void); | |
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38 | ENGINE *ENGINE_get_default_ECDH(void); |
39 | ENGINE *ENGINE_get_default_ECDSA(void); | |
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40 | ENGINE *ENGINE_get_default_DH(void); |
41 | ENGINE *ENGINE_get_default_RAND(void); | |
42 | ENGINE *ENGINE_get_cipher_engine(int nid); | |
43 | ENGINE *ENGINE_get_digest_engine(int nid); | |
44 | ||
45 | int ENGINE_set_default_RSA(ENGINE *e); | |
46 | int ENGINE_set_default_DSA(ENGINE *e); | |
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47 | int ENGINE_set_default_ECDH(ENGINE *e); |
48 | int ENGINE_set_default_ECDSA(ENGINE *e); | |
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49 | int ENGINE_set_default_DH(ENGINE *e); |
50 | int ENGINE_set_default_RAND(ENGINE *e); | |
51 | int ENGINE_set_default_ciphers(ENGINE *e); | |
52 | int ENGINE_set_default_digests(ENGINE *e); | |
53 | int ENGINE_set_default_string(ENGINE *e, const char *list); | |
54 | ||
55 | int ENGINE_set_default(ENGINE *e, unsigned int flags); | |
56 | ||
57 | unsigned int ENGINE_get_table_flags(void); | |
58 | void ENGINE_set_table_flags(unsigned int flags); | |
59 | ||
60 | int ENGINE_register_RSA(ENGINE *e); | |
61 | void ENGINE_unregister_RSA(ENGINE *e); | |
62 | void ENGINE_register_all_RSA(void); | |
63 | int ENGINE_register_DSA(ENGINE *e); | |
64 | void ENGINE_unregister_DSA(ENGINE *e); | |
65 | void ENGINE_register_all_DSA(void); | |
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66 | int ENGINE_register_ECDH(ENGINE *e); |
67 | void ENGINE_unregister_ECDH(ENGINE *e); | |
68 | void ENGINE_register_all_ECDH(void); | |
69 | int ENGINE_register_ECDSA(ENGINE *e); | |
70 | void ENGINE_unregister_ECDSA(ENGINE *e); | |
71 | void ENGINE_register_all_ECDSA(void); | |
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72 | int ENGINE_register_DH(ENGINE *e); |
73 | void ENGINE_unregister_DH(ENGINE *e); | |
74 | void ENGINE_register_all_DH(void); | |
75 | int ENGINE_register_RAND(ENGINE *e); | |
76 | void ENGINE_unregister_RAND(ENGINE *e); | |
77 | void ENGINE_register_all_RAND(void); | |
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78 | int ENGINE_register_STORE(ENGINE *e); |
79 | void ENGINE_unregister_STORE(ENGINE *e); | |
80 | void ENGINE_register_all_STORE(void); | |
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81 | int ENGINE_register_ciphers(ENGINE *e); |
82 | void ENGINE_unregister_ciphers(ENGINE *e); | |
83 | void ENGINE_register_all_ciphers(void); | |
84 | int ENGINE_register_digests(ENGINE *e); | |
85 | void ENGINE_unregister_digests(ENGINE *e); | |
86 | void ENGINE_register_all_digests(void); | |
87 | int ENGINE_register_complete(ENGINE *e); | |
88 | int ENGINE_register_all_complete(void); | |
89 | ||
6a659296 | 90 | int ENGINE_ctrl(ENGINE *e, int cmd, long i, void *p, void (*f)(void)); |
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91 | int ENGINE_cmd_is_executable(ENGINE *e, int cmd); |
92 | int ENGINE_ctrl_cmd(ENGINE *e, const char *cmd_name, | |
6a659296 | 93 | long i, void *p, void (*f)(void), int cmd_optional); |
3f90e450 | 94 | int ENGINE_ctrl_cmd_string(ENGINE *e, const char *cmd_name, const char *arg, |
6a659296 | 95 | int cmd_optional); |
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96 | |
97 | int ENGINE_set_ex_data(ENGINE *e, int idx, void *arg); | |
98 | void *ENGINE_get_ex_data(const ENGINE *e, int idx); | |
99 | ||
100 | int ENGINE_get_ex_new_index(long argl, void *argp, CRYPTO_EX_new *new_func, | |
101 | CRYPTO_EX_dup *dup_func, CRYPTO_EX_free *free_func); | |
102 | ||
103 | ENGINE *ENGINE_new(void); | |
104 | int ENGINE_free(ENGINE *e); | |
6a659296 | 105 | int ENGINE_up_ref(ENGINE *e); |
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106 | |
107 | int ENGINE_set_id(ENGINE *e, const char *id); | |
108 | int ENGINE_set_name(ENGINE *e, const char *name); | |
109 | int ENGINE_set_RSA(ENGINE *e, const RSA_METHOD *rsa_meth); | |
110 | int ENGINE_set_DSA(ENGINE *e, const DSA_METHOD *dsa_meth); | |
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111 | int ENGINE_set_ECDH(ENGINE *e, const ECDH_METHOD *dh_meth); |
112 | int ENGINE_set_ECDSA(ENGINE *e, const ECDSA_METHOD *dh_meth); | |
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113 | int ENGINE_set_DH(ENGINE *e, const DH_METHOD *dh_meth); |
114 | int ENGINE_set_RAND(ENGINE *e, const RAND_METHOD *rand_meth); | |
6a659296 | 115 | int ENGINE_set_STORE(ENGINE *e, const STORE_METHOD *rand_meth); |
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116 | int ENGINE_set_destroy_function(ENGINE *e, ENGINE_GEN_INT_FUNC_PTR destroy_f); |
117 | int ENGINE_set_init_function(ENGINE *e, ENGINE_GEN_INT_FUNC_PTR init_f); | |
118 | int ENGINE_set_finish_function(ENGINE *e, ENGINE_GEN_INT_FUNC_PTR finish_f); | |
119 | int ENGINE_set_ctrl_function(ENGINE *e, ENGINE_CTRL_FUNC_PTR ctrl_f); | |
120 | int ENGINE_set_load_privkey_function(ENGINE *e, ENGINE_LOAD_KEY_PTR loadpriv_f); | |
121 | int ENGINE_set_load_pubkey_function(ENGINE *e, ENGINE_LOAD_KEY_PTR loadpub_f); | |
122 | int ENGINE_set_ciphers(ENGINE *e, ENGINE_CIPHERS_PTR f); | |
123 | int ENGINE_set_digests(ENGINE *e, ENGINE_DIGESTS_PTR f); | |
124 | int ENGINE_set_flags(ENGINE *e, int flags); | |
125 | int ENGINE_set_cmd_defns(ENGINE *e, const ENGINE_CMD_DEFN *defns); | |
126 | ||
127 | const char *ENGINE_get_id(const ENGINE *e); | |
128 | const char *ENGINE_get_name(const ENGINE *e); | |
129 | const RSA_METHOD *ENGINE_get_RSA(const ENGINE *e); | |
130 | const DSA_METHOD *ENGINE_get_DSA(const ENGINE *e); | |
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131 | const ECDH_METHOD *ENGINE_get_ECDH(const ENGINE *e); |
132 | const ECDSA_METHOD *ENGINE_get_ECDSA(const ENGINE *e); | |
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133 | const DH_METHOD *ENGINE_get_DH(const ENGINE *e); |
134 | const RAND_METHOD *ENGINE_get_RAND(const ENGINE *e); | |
6a659296 | 135 | const STORE_METHOD *ENGINE_get_STORE(const ENGINE *e); |
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136 | ENGINE_GEN_INT_FUNC_PTR ENGINE_get_destroy_function(const ENGINE *e); |
137 | ENGINE_GEN_INT_FUNC_PTR ENGINE_get_init_function(const ENGINE *e); | |
138 | ENGINE_GEN_INT_FUNC_PTR ENGINE_get_finish_function(const ENGINE *e); | |
139 | ENGINE_CTRL_FUNC_PTR ENGINE_get_ctrl_function(const ENGINE *e); | |
140 | ENGINE_LOAD_KEY_PTR ENGINE_get_load_privkey_function(const ENGINE *e); | |
141 | ENGINE_LOAD_KEY_PTR ENGINE_get_load_pubkey_function(const ENGINE *e); | |
142 | ENGINE_CIPHERS_PTR ENGINE_get_ciphers(const ENGINE *e); | |
143 | ENGINE_DIGESTS_PTR ENGINE_get_digests(const ENGINE *e); | |
144 | const EVP_CIPHER *ENGINE_get_cipher(ENGINE *e, int nid); | |
145 | const EVP_MD *ENGINE_get_digest(ENGINE *e, int nid); | |
146 | int ENGINE_get_flags(const ENGINE *e); | |
147 | const ENGINE_CMD_DEFN *ENGINE_get_cmd_defns(const ENGINE *e); | |
148 | ||
149 | EVP_PKEY *ENGINE_load_private_key(ENGINE *e, const char *key_id, | |
150 | UI_METHOD *ui_method, void *callback_data); | |
151 | EVP_PKEY *ENGINE_load_public_key(ENGINE *e, const char *key_id, | |
152 | UI_METHOD *ui_method, void *callback_data); | |
153 | ||
154 | void ENGINE_add_conf_module(void); | |
155 | ||
156 | =head1 DESCRIPTION | |
157 | ||
158 | These functions create, manipulate, and use cryptographic modules in the | |
159 | form of B<ENGINE> objects. These objects act as containers for | |
160 | implementations of cryptographic algorithms, and support a | |
161 | reference-counted mechanism to allow them to be dynamically loaded in and | |
162 | out of the running application. | |
163 | ||
164 | The cryptographic functionality that can be provided by an B<ENGINE> | |
165 | implementation includes the following abstractions; | |
166 | ||
167 | RSA_METHOD - for providing alternative RSA implementations | |
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168 | DSA_METHOD, DH_METHOD, RAND_METHOD, ECDH_METHOD, ECDSA_METHOD, |
169 | STORE_METHOD - similarly for other OpenSSL APIs | |
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170 | EVP_CIPHER - potentially multiple cipher algorithms (indexed by 'nid') |
171 | EVP_DIGEST - potentially multiple hash algorithms (indexed by 'nid') | |
172 | key-loading - loading public and/or private EVP_PKEY keys | |
173 | ||
174 | =head2 Reference counting and handles | |
175 | ||
176 | Due to the modular nature of the ENGINE API, pointers to ENGINEs need to be | |
177 | treated as handles - ie. not only as pointers, but also as references to | |
6a659296 | 178 | the underlying ENGINE object. Ie. one should obtain a new reference when |
3f90e450 | 179 | making copies of an ENGINE pointer if the copies will be used (and |
b6a338cb | 180 | released) independently. |
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181 | |
182 | ENGINE objects have two levels of reference-counting to match the way in | |
183 | which the objects are used. At the most basic level, each ENGINE pointer is | |
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184 | inherently a B<structural> reference - a structural reference is required |
185 | to use the pointer value at all, as this kind of reference is a guarantee | |
186 | that the structure can not be deallocated until the reference is released. | |
187 | ||
188 | However, a structural reference provides no guarantee that the ENGINE is | |
740ceb5b | 189 | initialised and able to use any of its cryptographic |
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190 | implementations. Indeed it's quite possible that most ENGINEs will not |
191 | initialise at all in typical environments, as ENGINEs are typically used to | |
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192 | support specialised hardware. To use an ENGINE's functionality, you need a |
193 | B<functional> reference. This kind of reference can be considered a | |
194 | specialised form of structural reference, because each functional reference | |
195 | implicitly contains a structural reference as well - however to avoid | |
196 | difficult-to-find programming bugs, it is recommended to treat the two | |
b6a338cb | 197 | kinds of reference independently. If you have a functional reference to an |
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198 | ENGINE, you have a guarantee that the ENGINE has been initialised and |
199 | is ready to perform cryptographic operations, and will remain initialised | |
6a659296 | 200 | until after you have released your reference. |
3f90e450 | 201 | |
4390d661 | 202 | I<Structural references> |
3f90e450 | 203 | |
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204 | This basic type of reference is used for instantiating new ENGINEs, |
205 | iterating across OpenSSL's internal linked-list of loaded | |
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206 | ENGINEs, reading information about an ENGINE, etc. Essentially a structural |
207 | reference is sufficient if you only need to query or manipulate the data of | |
208 | an ENGINE implementation rather than use its functionality. | |
209 | ||
210 | The ENGINE_new() function returns a structural reference to a new (empty) | |
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211 | ENGINE object. There are other ENGINE API functions that return structural |
212 | references such as; ENGINE_by_id(), ENGINE_get_first(), ENGINE_get_last(), | |
213 | ENGINE_get_next(), ENGINE_get_prev(). All structural references should be | |
214 | released by a corresponding to call to the ENGINE_free() function - the | |
215 | ENGINE object itself will only actually be cleaned up and deallocated when | |
216 | the last structural reference is released. | |
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217 | |
218 | It should also be noted that many ENGINE API function calls that accept a | |
219 | structural reference will internally obtain another reference - typically | |
220 | this happens whenever the supplied ENGINE will be needed by OpenSSL after | |
221 | the function has returned. Eg. the function to add a new ENGINE to | |
222 | OpenSSL's internal list is ENGINE_add() - if this function returns success, | |
223 | then OpenSSL will have stored a new structural reference internally so the | |
224 | caller is still responsible for freeing their own reference with | |
225 | ENGINE_free() when they are finished with it. In a similar way, some | |
226 | functions will automatically release the structural reference passed to it | |
227 | if part of the function's job is to do so. Eg. the ENGINE_get_next() and | |
228 | ENGINE_get_prev() functions are used for iterating across the internal | |
229 | ENGINE list - they will return a new structural reference to the next (or | |
230 | previous) ENGINE in the list or NULL if at the end (or beginning) of the | |
231 | list, but in either case the structural reference passed to the function is | |
232 | released on behalf of the caller. | |
233 | ||
234 | To clarify a particular function's handling of references, one should | |
235 | always consult that function's documentation "man" page, or failing that | |
236 | the openssl/engine.h header file includes some hints. | |
237 | ||
4390d661 | 238 | I<Functional references> |
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239 | |
240 | As mentioned, functional references exist when the cryptographic | |
241 | functionality of an ENGINE is required to be available. A functional | |
242 | reference can be obtained in one of two ways; from an existing structural | |
243 | reference to the required ENGINE, or by asking OpenSSL for the default | |
244 | operational ENGINE for a given cryptographic purpose. | |
245 | ||
246 | To obtain a functional reference from an existing structural reference, | |
247 | call the ENGINE_init() function. This returns zero if the ENGINE was not | |
248 | already operational and couldn't be successfully initialised (eg. lack of | |
249 | system drivers, no special hardware attached, etc), otherwise it will | |
250 | return non-zero to indicate that the ENGINE is now operational and will | |
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251 | have allocated a new B<functional> reference to the ENGINE. All functional |
252 | references are released by calling ENGINE_finish() (which removes the | |
253 | implicit structural reference as well). | |
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254 | |
255 | The second way to get a functional reference is by asking OpenSSL for a | |
256 | default implementation for a given task, eg. by ENGINE_get_default_RSA(), | |
257 | ENGINE_get_default_cipher_engine(), etc. These are discussed in the next | |
258 | section, though they are not usually required by application programmers as | |
259 | they are used automatically when creating and using the relevant | |
260 | algorithm-specific types in OpenSSL, such as RSA, DSA, EVP_CIPHER_CTX, etc. | |
261 | ||
262 | =head2 Default implementations | |
263 | ||
264 | For each supported abstraction, the ENGINE code maintains an internal table | |
265 | of state to control which implementations are available for a given | |
266 | abstraction and which should be used by default. These implementations are | |
6a659296 | 267 | registered in the tables and indexed by an 'nid' value, because |
3f90e450 | 268 | abstractions like EVP_CIPHER and EVP_DIGEST support many distinct |
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269 | algorithms and modes, and ENGINEs can support arbitrarily many of them. |
270 | In the case of other abstractions like RSA, DSA, etc, there is only one | |
271 | "algorithm" so all implementations implicitly register using the same 'nid' | |
272 | index. | |
273 | ||
274 | When a default ENGINE is requested for a given abstraction/algorithm/mode, (eg. | |
275 | when calling RSA_new_method(NULL)), a "get_default" call will be made to the | |
276 | ENGINE subsystem to process the corresponding state table and return a | |
277 | functional reference to an initialised ENGINE whose implementation should be | |
278 | used. If no ENGINE should (or can) be used, it will return NULL and the caller | |
279 | will operate with a NULL ENGINE handle - this usually equates to using the | |
280 | conventional software implementation. In the latter case, OpenSSL will from | |
281 | then on behave the way it used to before the ENGINE API existed. | |
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282 | |
283 | Each state table has a flag to note whether it has processed this | |
284 | "get_default" query since the table was last modified, because to process | |
285 | this question it must iterate across all the registered ENGINEs in the | |
286 | table trying to initialise each of them in turn, in case one of them is | |
287 | operational. If it returns a functional reference to an ENGINE, it will | |
288 | also cache another reference to speed up processing future queries (without | |
289 | needing to iterate across the table). Likewise, it will cache a NULL | |
290 | response if no ENGINE was available so that future queries won't repeat the | |
291 | same iteration unless the state table changes. This behaviour can also be | |
292 | changed; if the ENGINE_TABLE_FLAG_NOINIT flag is set (using | |
293 | ENGINE_set_table_flags()), no attempted initialisations will take place, | |
294 | instead the only way for the state table to return a non-NULL ENGINE to the | |
295 | "get_default" query will be if one is expressly set in the table. Eg. | |
296 | ENGINE_set_default_RSA() does the same job as ENGINE_register_RSA() except | |
297 | that it also sets the state table's cached response for the "get_default" | |
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298 | query. In the case of abstractions like EVP_CIPHER, where implementations are |
299 | indexed by 'nid', these flags and cached-responses are distinct for each 'nid' | |
300 | value. | |
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301 | |
302 | =head2 Application requirements | |
303 | ||
304 | This section will explain the basic things an application programmer should | |
305 | support to make the most useful elements of the ENGINE functionality | |
306 | available to the user. The first thing to consider is whether the | |
307 | programmer wishes to make alternative ENGINE modules available to the | |
308 | application and user. OpenSSL maintains an internal linked list of | |
309 | "visible" ENGINEs from which it has to operate - at start-up, this list is | |
310 | empty and in fact if an application does not call any ENGINE API calls and | |
311 | it uses static linking against openssl, then the resulting application | |
312 | binary will not contain any alternative ENGINE code at all. So the first | |
313 | consideration is whether any/all available ENGINE implementations should be | |
314 | made visible to OpenSSL - this is controlled by calling the various "load" | |
315 | functions, eg. | |
316 | ||
317 | /* Make the "dynamic" ENGINE available */ | |
318 | void ENGINE_load_dynamic(void); | |
319 | /* Make the CryptoSwift hardware acceleration support available */ | |
320 | void ENGINE_load_cswift(void); | |
321 | /* Make support for nCipher's "CHIL" hardware available */ | |
322 | void ENGINE_load_chil(void); | |
323 | ... | |
324 | /* Make ALL ENGINE implementations bundled with OpenSSL available */ | |
325 | void ENGINE_load_builtin_engines(void); | |
326 | ||
327 | Having called any of these functions, ENGINE objects would have been | |
328 | dynamically allocated and populated with these implementations and linked | |
329 | into OpenSSL's internal linked list. At this point it is important to | |
330 | mention an important API function; | |
331 | ||
332 | void ENGINE_cleanup(void); | |
333 | ||
334 | If no ENGINE API functions are called at all in an application, then there | |
335 | are no inherent memory leaks to worry about from the ENGINE functionality, | |
6a659296 | 336 | however if any ENGINEs are loaded, even if they are never registered or |
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337 | used, it is necessary to use the ENGINE_cleanup() function to |
338 | correspondingly cleanup before program exit, if the caller wishes to avoid | |
339 | memory leaks. This mechanism uses an internal callback registration table | |
340 | so that any ENGINE API functionality that knows it requires cleanup can | |
341 | register its cleanup details to be called during ENGINE_cleanup(). This | |
342 | approach allows ENGINE_cleanup() to clean up after any ENGINE functionality | |
343 | at all that your program uses, yet doesn't automatically create linker | |
344 | dependencies to all possible ENGINE functionality - only the cleanup | |
345 | callbacks required by the functionality you do use will be required by the | |
346 | linker. | |
347 | ||
348 | The fact that ENGINEs are made visible to OpenSSL (and thus are linked into | |
349 | the program and loaded into memory at run-time) does not mean they are | |
350 | "registered" or called into use by OpenSSL automatically - that behaviour | |
6a659296 | 351 | is something for the application to control. Some applications |
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352 | will want to allow the user to specify exactly which ENGINE they want used |
353 | if any is to be used at all. Others may prefer to load all support and have | |
354 | OpenSSL automatically use at run-time any ENGINE that is able to | |
355 | successfully initialise - ie. to assume that this corresponds to | |
356 | acceleration hardware attached to the machine or some such thing. There are | |
357 | probably numerous other ways in which applications may prefer to handle | |
358 | things, so we will simply illustrate the consequences as they apply to a | |
359 | couple of simple cases and leave developers to consider these and the | |
360 | source code to openssl's builtin utilities as guides. | |
361 | ||
4390d661 | 362 | I<Using a specific ENGINE implementation> |
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363 | |
364 | Here we'll assume an application has been configured by its user or admin | |
365 | to want to use the "ACME" ENGINE if it is available in the version of | |
366 | OpenSSL the application was compiled with. If it is available, it should be | |
740ceb5b | 367 | used by default for all RSA, DSA, and symmetric cipher operations, otherwise |
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368 | OpenSSL should use its builtin software as per usual. The following code |
369 | illustrates how to approach this; | |
370 | ||
371 | ENGINE *e; | |
372 | const char *engine_id = "ACME"; | |
373 | ENGINE_load_builtin_engines(); | |
374 | e = ENGINE_by_id(engine_id); | |
375 | if(!e) | |
376 | /* the engine isn't available */ | |
377 | return; | |
378 | if(!ENGINE_init(e)) { | |
379 | /* the engine couldn't initialise, release 'e' */ | |
380 | ENGINE_free(e); | |
381 | return; | |
382 | } | |
383 | if(!ENGINE_set_default_RSA(e)) | |
384 | /* This should only happen when 'e' can't initialise, but the previous | |
385 | * statement suggests it did. */ | |
386 | abort(); | |
387 | ENGINE_set_default_DSA(e); | |
388 | ENGINE_set_default_ciphers(e); | |
389 | /* Release the functional reference from ENGINE_init() */ | |
390 | ENGINE_finish(e); | |
391 | /* Release the structural reference from ENGINE_by_id() */ | |
392 | ENGINE_free(e); | |
393 | ||
4390d661 | 394 | I<Automatically using builtin ENGINE implementations> |
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395 | |
396 | Here we'll assume we want to load and register all ENGINE implementations | |
397 | bundled with OpenSSL, such that for any cryptographic algorithm required by | |
740ceb5b | 398 | OpenSSL - if there is an ENGINE that implements it and can be initialised, |
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399 | it should be used. The following code illustrates how this can work; |
400 | ||
401 | /* Load all bundled ENGINEs into memory and make them visible */ | |
402 | ENGINE_load_builtin_engines(); | |
403 | /* Register all of them for every algorithm they collectively implement */ | |
404 | ENGINE_register_all_complete(); | |
405 | ||
406 | That's all that's required. Eg. the next time OpenSSL tries to set up an | |
407 | RSA key, any bundled ENGINEs that implement RSA_METHOD will be passed to | |
408 | ENGINE_init() and if any of those succeed, that ENGINE will be set as the | |
6a659296 | 409 | default for RSA use from then on. |
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410 | |
411 | =head2 Advanced configuration support | |
412 | ||
413 | There is a mechanism supported by the ENGINE framework that allows each | |
414 | ENGINE implementation to define an arbitrary set of configuration | |
415 | "commands" and expose them to OpenSSL and any applications based on | |
416 | OpenSSL. This mechanism is entirely based on the use of name-value pairs | |
6a659296 | 417 | and assumes ASCII input (no unicode or UTF for now!), so it is ideal if |
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418 | applications want to provide a transparent way for users to provide |
419 | arbitrary configuration "directives" directly to such ENGINEs. It is also | |
420 | possible for the application to dynamically interrogate the loaded ENGINE | |
421 | implementations for the names, descriptions, and input flags of their | |
422 | available "control commands", providing a more flexible configuration | |
423 | scheme. However, if the user is expected to know which ENGINE device he/she | |
424 | is using (in the case of specialised hardware, this goes without saying) | |
425 | then applications may not need to concern themselves with discovering the | |
6a659296 GT |
426 | supported control commands and simply prefer to pass settings into ENGINEs |
427 | exactly as they are provided by the user. | |
3f90e450 GT |
428 | |
429 | Before illustrating how control commands work, it is worth mentioning what | |
430 | they are typically used for. Broadly speaking there are two uses for | |
431 | control commands; the first is to provide the necessary details to the | |
432 | implementation (which may know nothing at all specific to the host system) | |
433 | so that it can be initialised for use. This could include the path to any | |
434 | driver or config files it needs to load, required network addresses, | |
6a659296 | 435 | smart-card identifiers, passwords to initialise protected devices, |
3f90e450 GT |
436 | logging information, etc etc. This class of commands typically needs to be |
437 | passed to an ENGINE B<before> attempting to initialise it, ie. before | |
438 | calling ENGINE_init(). The other class of commands consist of settings or | |
439 | operations that tweak certain behaviour or cause certain operations to take | |
440 | place, and these commands may work either before or after ENGINE_init(), or | |
6a659296 | 441 | in some cases both. ENGINE implementations should provide indications of |
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442 | this in the descriptions attached to builtin control commands and/or in |
443 | external product documentation. | |
444 | ||
4390d661 | 445 | I<Issuing control commands to an ENGINE> |
3f90e450 GT |
446 | |
447 | Let's illustrate by example; a function for which the caller supplies the | |
448 | name of the ENGINE it wishes to use, a table of string-pairs for use before | |
449 | initialisation, and another table for use after initialisation. Note that | |
450 | the string-pairs used for control commands consist of a command "name" | |
451 | followed by the command "parameter" - the parameter could be NULL in some | |
452 | cases but the name can not. This function should initialise the ENGINE | |
453 | (issuing the "pre" commands beforehand and the "post" commands afterwards) | |
454 | and set it as the default for everything except RAND and then return a | |
455 | boolean success or failure. | |
456 | ||
457 | int generic_load_engine_fn(const char *engine_id, | |
458 | const char **pre_cmds, int pre_num, | |
459 | const char **post_cmds, int post_num) | |
460 | { | |
461 | ENGINE *e = ENGINE_by_id(engine_id); | |
462 | if(!e) return 0; | |
463 | while(pre_num--) { | |
464 | if(!ENGINE_ctrl_cmd_string(e, pre_cmds[0], pre_cmds[1], 0)) { | |
465 | fprintf(stderr, "Failed command (%s - %s:%s)\n", engine_id, | |
466 | pre_cmds[0], pre_cmds[1] ? pre_cmds[1] : "(NULL)"); | |
467 | ENGINE_free(e); | |
468 | return 0; | |
469 | } | |
470 | pre_cmds += 2; | |
471 | } | |
472 | if(!ENGINE_init(e)) { | |
473 | fprintf(stderr, "Failed initialisation\n"); | |
474 | ENGINE_free(e); | |
475 | return 0; | |
476 | } | |
477 | /* ENGINE_init() returned a functional reference, so free the structural | |
478 | * reference from ENGINE_by_id(). */ | |
479 | ENGINE_free(e); | |
480 | while(post_num--) { | |
481 | if(!ENGINE_ctrl_cmd_string(e, post_cmds[0], post_cmds[1], 0)) { | |
482 | fprintf(stderr, "Failed command (%s - %s:%s)\n", engine_id, | |
483 | post_cmds[0], post_cmds[1] ? post_cmds[1] : "(NULL)"); | |
484 | ENGINE_finish(e); | |
485 | return 0; | |
486 | } | |
487 | post_cmds += 2; | |
488 | } | |
489 | ENGINE_set_default(e, ENGINE_METHOD_ALL & ~ENGINE_METHOD_RAND); | |
490 | /* Success */ | |
491 | return 1; | |
492 | } | |
493 | ||
494 | Note that ENGINE_ctrl_cmd_string() accepts a boolean argument that can | |
495 | relax the semantics of the function - if set non-zero it will only return | |
496 | failure if the ENGINE supported the given command name but failed while | |
497 | executing it, if the ENGINE doesn't support the command name it will simply | |
498 | return success without doing anything. In this case we assume the user is | |
499 | only supplying commands specific to the given ENGINE so we set this to | |
500 | FALSE. | |
501 | ||
4390d661 | 502 | I<Discovering supported control commands> |
3f90e450 GT |
503 | |
504 | It is possible to discover at run-time the names, numerical-ids, descriptions | |
6a659296 GT |
505 | and input parameters of the control commands supported by an ENGINE using a |
506 | structural reference. Note that some control commands are defined by OpenSSL | |
507 | itself and it will intercept and handle these control commands on behalf of the | |
508 | ENGINE, ie. the ENGINE's ctrl() handler is not used for the control command. | |
509 | openssl/engine.h defines an index, ENGINE_CMD_BASE, that all control commands | |
510 | implemented by ENGINEs should be numbered from. Any command value lower than | |
511 | this symbol is considered a "generic" command is handled directly by the | |
512 | OpenSSL core routines. | |
3f90e450 GT |
513 | |
514 | It is using these "core" control commands that one can discover the the control | |
515 | commands implemented by a given ENGINE, specifically the commands; | |
516 | ||
517 | #define ENGINE_HAS_CTRL_FUNCTION 10 | |
518 | #define ENGINE_CTRL_GET_FIRST_CMD_TYPE 11 | |
519 | #define ENGINE_CTRL_GET_NEXT_CMD_TYPE 12 | |
520 | #define ENGINE_CTRL_GET_CMD_FROM_NAME 13 | |
521 | #define ENGINE_CTRL_GET_NAME_LEN_FROM_CMD 14 | |
522 | #define ENGINE_CTRL_GET_NAME_FROM_CMD 15 | |
523 | #define ENGINE_CTRL_GET_DESC_LEN_FROM_CMD 16 | |
524 | #define ENGINE_CTRL_GET_DESC_FROM_CMD 17 | |
525 | #define ENGINE_CTRL_GET_CMD_FLAGS 18 | |
526 | ||
527 | Whilst these commands are automatically processed by the OpenSSL framework code, | |
6a659296 GT |
528 | they use various properties exposed by each ENGINE to process these |
529 | queries. An ENGINE has 3 properties it exposes that can affect how this behaves; | |
3f90e450 GT |
530 | it can supply a ctrl() handler, it can specify ENGINE_FLAGS_MANUAL_CMD_CTRL in |
531 | the ENGINE's flags, and it can expose an array of control command descriptions. | |
532 | If an ENGINE specifies the ENGINE_FLAGS_MANUAL_CMD_CTRL flag, then it will | |
533 | simply pass all these "core" control commands directly to the ENGINE's ctrl() | |
534 | handler (and thus, it must have supplied one), so it is up to the ENGINE to | |
535 | reply to these "discovery" commands itself. If that flag is not set, then the | |
536 | OpenSSL framework code will work with the following rules; | |
537 | ||
538 | if no ctrl() handler supplied; | |
539 | ENGINE_HAS_CTRL_FUNCTION returns FALSE (zero), | |
540 | all other commands fail. | |
541 | if a ctrl() handler was supplied but no array of control commands; | |
542 | ENGINE_HAS_CTRL_FUNCTION returns TRUE, | |
543 | all other commands fail. | |
544 | if a ctrl() handler and array of control commands was supplied; | |
545 | ENGINE_HAS_CTRL_FUNCTION returns TRUE, | |
546 | all other commands proceed processing ... | |
547 | ||
548 | If the ENGINE's array of control commands is empty then all other commands will | |
549 | fail, otherwise; ENGINE_CTRL_GET_FIRST_CMD_TYPE returns the identifier of | |
550 | the first command supported by the ENGINE, ENGINE_GET_NEXT_CMD_TYPE takes the | |
551 | identifier of a command supported by the ENGINE and returns the next command | |
552 | identifier or fails if there are no more, ENGINE_CMD_FROM_NAME takes a string | |
553 | name for a command and returns the corresponding identifier or fails if no such | |
554 | command name exists, and the remaining commands take a command identifier and | |
555 | return properties of the corresponding commands. All except | |
556 | ENGINE_CTRL_GET_FLAGS return the string length of a command name or description, | |
557 | or populate a supplied character buffer with a copy of the command name or | |
558 | description. ENGINE_CTRL_GET_FLAGS returns a bitwise-OR'd mask of the following | |
559 | possible values; | |
560 | ||
561 | #define ENGINE_CMD_FLAG_NUMERIC (unsigned int)0x0001 | |
562 | #define ENGINE_CMD_FLAG_STRING (unsigned int)0x0002 | |
563 | #define ENGINE_CMD_FLAG_NO_INPUT (unsigned int)0x0004 | |
564 | #define ENGINE_CMD_FLAG_INTERNAL (unsigned int)0x0008 | |
565 | ||
566 | If the ENGINE_CMD_FLAG_INTERNAL flag is set, then any other flags are purely | |
567 | informational to the caller - this flag will prevent the command being usable | |
568 | for any higher-level ENGINE functions such as ENGINE_ctrl_cmd_string(). | |
569 | "INTERNAL" commands are not intended to be exposed to text-based configuration | |
570 | by applications, administrations, users, etc. These can support arbitrary | |
571 | operations via ENGINE_ctrl(), including passing to and/or from the control | |
572 | commands data of any arbitrary type. These commands are supported in the | |
186bb907 | 573 | discovery mechanisms simply to allow applications to determine if an ENGINE |
3f90e450 GT |
574 | supports certain specific commands it might want to use (eg. application "foo" |
575 | might query various ENGINEs to see if they implement "FOO_GET_VENDOR_LOGO_GIF" - | |
576 | and ENGINE could therefore decide whether or not to support this "foo"-specific | |
577 | extension). | |
578 | ||
579 | =head2 Future developments | |
580 | ||
581 | The ENGINE API and internal architecture is currently being reviewed. Slated for | |
582 | possible release in 0.9.8 is support for transparent loading of "dynamic" | |
583 | ENGINEs (built as self-contained shared-libraries). This would allow ENGINE | |
b6a338cb | 584 | implementations to be provided independently of OpenSSL libraries and/or |
3f90e450 GT |
585 | OpenSSL-based applications, and would also remove any requirement for |
586 | applications to explicitly use the "dynamic" ENGINE to bind to shared-library | |
587 | implementations. | |
588 | ||
589 | =head1 SEE ALSO | |
590 | ||
9b86974e | 591 | L<rsa(3)>, L<dsa(3)>, L<dh(3)>, L<rand(3)> |
3f90e450 GT |
592 | |
593 | =cut |