Merge branch 'vendor/OPENSSL'
[dragonfly.git] / secure / lib / libcrypto / man / engine.3
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129.\" ========================================================================
130.\"
131.IX Title "engine 3"
18ed9402 132.TH engine 3 "2008-09-27" "0.9.8i" "OpenSSL"
984263bc 133.SH "NAME"
74dab6c2 134engine \- ENGINE cryptographic module support
984263bc 135.SH "SYNOPSIS"
8b0cefbb 136.IX Header "SYNOPSIS"
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137.Vb 1
138\& #include <openssl/engine.h>
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139.Ve
140.PP
141.Vb 4
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142\& ENGINE *ENGINE_get_first(void);
143\& ENGINE *ENGINE_get_last(void);
144\& ENGINE *ENGINE_get_next(ENGINE *e);
145\& ENGINE *ENGINE_get_prev(ENGINE *e);
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146.Ve
147.PP
148.Vb 2
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149\& int ENGINE_add(ENGINE *e);
150\& int ENGINE_remove(ENGINE *e);
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151.Ve
152.PP
153.Vb 1
984263bc 154\& ENGINE *ENGINE_by_id(const char *id);
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155.Ve
156.PP
157.Vb 2
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158\& int ENGINE_init(ENGINE *e);
159\& int ENGINE_finish(ENGINE *e);
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160.Ve
161.PP
162.Vb 15
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163\& void ENGINE_load_openssl(void);
164\& void ENGINE_load_dynamic(void);
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165\& #ifndef OPENSSL_NO_STATIC_ENGINE
166\& void ENGINE_load_4758cca(void);
167\& void ENGINE_load_aep(void);
984263bc 168\& void ENGINE_load_atalla(void);
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169\& void ENGINE_load_chil(void);
170\& void ENGINE_load_cswift(void);
171\& void ENGINE_load_gmp(void);
984263bc 172\& void ENGINE_load_nuron(void);
984263bc 173\& void ENGINE_load_sureware(void);
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174\& void ENGINE_load_ubsec(void);
175\& #endif
176\& void ENGINE_load_cryptodev(void);
984263bc 177\& void ENGINE_load_builtin_engines(void);
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178.Ve
179.PP
180.Vb 1
984263bc 181\& void ENGINE_cleanup(void);
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182.Ve
183.PP
184.Vb 8
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185\& ENGINE *ENGINE_get_default_RSA(void);
186\& ENGINE *ENGINE_get_default_DSA(void);
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187\& ENGINE *ENGINE_get_default_ECDH(void);
188\& ENGINE *ENGINE_get_default_ECDSA(void);
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189\& ENGINE *ENGINE_get_default_DH(void);
190\& ENGINE *ENGINE_get_default_RAND(void);
191\& ENGINE *ENGINE_get_cipher_engine(int nid);
192\& ENGINE *ENGINE_get_digest_engine(int nid);
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193.Ve
194.PP
195.Vb 9
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196\& int ENGINE_set_default_RSA(ENGINE *e);
197\& int ENGINE_set_default_DSA(ENGINE *e);
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198\& int ENGINE_set_default_ECDH(ENGINE *e);
199\& int ENGINE_set_default_ECDSA(ENGINE *e);
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200\& int ENGINE_set_default_DH(ENGINE *e);
201\& int ENGINE_set_default_RAND(ENGINE *e);
202\& int ENGINE_set_default_ciphers(ENGINE *e);
203\& int ENGINE_set_default_digests(ENGINE *e);
204\& int ENGINE_set_default_string(ENGINE *e, const char *list);
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205.Ve
206.PP
207.Vb 1
984263bc 208\& int ENGINE_set_default(ENGINE *e, unsigned int flags);
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209.Ve
210.PP
211.Vb 2
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212\& unsigned int ENGINE_get_table_flags(void);
213\& void ENGINE_set_table_flags(unsigned int flags);
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214.Ve
215.PP
216.Vb 29
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217\& int ENGINE_register_RSA(ENGINE *e);
218\& void ENGINE_unregister_RSA(ENGINE *e);
219\& void ENGINE_register_all_RSA(void);
220\& int ENGINE_register_DSA(ENGINE *e);
221\& void ENGINE_unregister_DSA(ENGINE *e);
222\& void ENGINE_register_all_DSA(void);
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223\& int ENGINE_register_ECDH(ENGINE *e);
224\& void ENGINE_unregister_ECDH(ENGINE *e);
225\& void ENGINE_register_all_ECDH(void);
226\& int ENGINE_register_ECDSA(ENGINE *e);
227\& void ENGINE_unregister_ECDSA(ENGINE *e);
228\& void ENGINE_register_all_ECDSA(void);
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229\& int ENGINE_register_DH(ENGINE *e);
230\& void ENGINE_unregister_DH(ENGINE *e);
231\& void ENGINE_register_all_DH(void);
232\& int ENGINE_register_RAND(ENGINE *e);
233\& void ENGINE_unregister_RAND(ENGINE *e);
234\& void ENGINE_register_all_RAND(void);
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235\& int ENGINE_register_STORE(ENGINE *e);
236\& void ENGINE_unregister_STORE(ENGINE *e);
237\& void ENGINE_register_all_STORE(void);
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238\& int ENGINE_register_ciphers(ENGINE *e);
239\& void ENGINE_unregister_ciphers(ENGINE *e);
240\& void ENGINE_register_all_ciphers(void);
241\& int ENGINE_register_digests(ENGINE *e);
242\& void ENGINE_unregister_digests(ENGINE *e);
243\& void ENGINE_register_all_digests(void);
244\& int ENGINE_register_complete(ENGINE *e);
245\& int ENGINE_register_all_complete(void);
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246.Ve
247.PP
248.Vb 6
a561f9ff 249\& int ENGINE_ctrl(ENGINE *e, int cmd, long i, void *p, void (*f)(void));
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250\& int ENGINE_cmd_is_executable(ENGINE *e, int cmd);
251\& int ENGINE_ctrl_cmd(ENGINE *e, const char *cmd_name,
a561f9ff 252\& long i, void *p, void (*f)(void), int cmd_optional);
984263bc 253\& int ENGINE_ctrl_cmd_string(ENGINE *e, const char *cmd_name, const char *arg,
a561f9ff 254\& int cmd_optional);
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255.Ve
256.PP
257.Vb 2
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258\& int ENGINE_set_ex_data(ENGINE *e, int idx, void *arg);
259\& void *ENGINE_get_ex_data(const ENGINE *e, int idx);
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260.Ve
261.PP
262.Vb 2
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263\& int ENGINE_get_ex_new_index(long argl, void *argp, CRYPTO_EX_new *new_func,
264\& CRYPTO_EX_dup *dup_func, CRYPTO_EX_free *free_func);
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265.Ve
266.PP
267.Vb 3
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268\& ENGINE *ENGINE_new(void);
269\& int ENGINE_free(ENGINE *e);
a561f9ff 270\& int ENGINE_up_ref(ENGINE *e);
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271.Ve
272.PP
273.Vb 19
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274\& int ENGINE_set_id(ENGINE *e, const char *id);
275\& int ENGINE_set_name(ENGINE *e, const char *name);
276\& int ENGINE_set_RSA(ENGINE *e, const RSA_METHOD *rsa_meth);
277\& int ENGINE_set_DSA(ENGINE *e, const DSA_METHOD *dsa_meth);
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278\& int ENGINE_set_ECDH(ENGINE *e, const ECDH_METHOD *dh_meth);
279\& int ENGINE_set_ECDSA(ENGINE *e, const ECDSA_METHOD *dh_meth);
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280\& int ENGINE_set_DH(ENGINE *e, const DH_METHOD *dh_meth);
281\& int ENGINE_set_RAND(ENGINE *e, const RAND_METHOD *rand_meth);
a561f9ff 282\& int ENGINE_set_STORE(ENGINE *e, const STORE_METHOD *rand_meth);
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283\& int ENGINE_set_destroy_function(ENGINE *e, ENGINE_GEN_INT_FUNC_PTR destroy_f);
284\& int ENGINE_set_init_function(ENGINE *e, ENGINE_GEN_INT_FUNC_PTR init_f);
285\& int ENGINE_set_finish_function(ENGINE *e, ENGINE_GEN_INT_FUNC_PTR finish_f);
286\& int ENGINE_set_ctrl_function(ENGINE *e, ENGINE_CTRL_FUNC_PTR ctrl_f);
287\& int ENGINE_set_load_privkey_function(ENGINE *e, ENGINE_LOAD_KEY_PTR loadpriv_f);
288\& int ENGINE_set_load_pubkey_function(ENGINE *e, ENGINE_LOAD_KEY_PTR loadpub_f);
289\& int ENGINE_set_ciphers(ENGINE *e, ENGINE_CIPHERS_PTR f);
290\& int ENGINE_set_digests(ENGINE *e, ENGINE_DIGESTS_PTR f);
291\& int ENGINE_set_flags(ENGINE *e, int flags);
292\& int ENGINE_set_cmd_defns(ENGINE *e, const ENGINE_CMD_DEFN *defns);
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293.Ve
294.PP
295.Vb 21
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296\& const char *ENGINE_get_id(const ENGINE *e);
297\& const char *ENGINE_get_name(const ENGINE *e);
298\& const RSA_METHOD *ENGINE_get_RSA(const ENGINE *e);
299\& const DSA_METHOD *ENGINE_get_DSA(const ENGINE *e);
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300\& const ECDH_METHOD *ENGINE_get_ECDH(const ENGINE *e);
301\& const ECDSA_METHOD *ENGINE_get_ECDSA(const ENGINE *e);
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302\& const DH_METHOD *ENGINE_get_DH(const ENGINE *e);
303\& const RAND_METHOD *ENGINE_get_RAND(const ENGINE *e);
a561f9ff 304\& const STORE_METHOD *ENGINE_get_STORE(const ENGINE *e);
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305\& ENGINE_GEN_INT_FUNC_PTR ENGINE_get_destroy_function(const ENGINE *e);
306\& ENGINE_GEN_INT_FUNC_PTR ENGINE_get_init_function(const ENGINE *e);
307\& ENGINE_GEN_INT_FUNC_PTR ENGINE_get_finish_function(const ENGINE *e);
308\& ENGINE_CTRL_FUNC_PTR ENGINE_get_ctrl_function(const ENGINE *e);
309\& ENGINE_LOAD_KEY_PTR ENGINE_get_load_privkey_function(const ENGINE *e);
310\& ENGINE_LOAD_KEY_PTR ENGINE_get_load_pubkey_function(const ENGINE *e);
311\& ENGINE_CIPHERS_PTR ENGINE_get_ciphers(const ENGINE *e);
312\& ENGINE_DIGESTS_PTR ENGINE_get_digests(const ENGINE *e);
313\& const EVP_CIPHER *ENGINE_get_cipher(ENGINE *e, int nid);
314\& const EVP_MD *ENGINE_get_digest(ENGINE *e, int nid);
315\& int ENGINE_get_flags(const ENGINE *e);
316\& const ENGINE_CMD_DEFN *ENGINE_get_cmd_defns(const ENGINE *e);
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317.Ve
318.PP
319.Vb 4
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320\& EVP_PKEY *ENGINE_load_private_key(ENGINE *e, const char *key_id,
321\& UI_METHOD *ui_method, void *callback_data);
322\& EVP_PKEY *ENGINE_load_public_key(ENGINE *e, const char *key_id,
323\& UI_METHOD *ui_method, void *callback_data);
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324.Ve
325.PP
326.Vb 1
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327\& void ENGINE_add_conf_module(void);
328.Ve
329.SH "DESCRIPTION"
8b0cefbb 330.IX Header "DESCRIPTION"
984263bc 331These functions create, manipulate, and use cryptographic modules in the
8b0cefbb 332form of \fB\s-1ENGINE\s0\fR objects. These objects act as containers for
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333implementations of cryptographic algorithms, and support a
334reference-counted mechanism to allow them to be dynamically loaded in and
335out of the running application.
336.PP
8b0cefbb 337The cryptographic functionality that can be provided by an \fB\s-1ENGINE\s0\fR
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338implementation includes the following abstractions;
339.PP
a561f9ff 340.Vb 6
aac4ff6f 341\& RSA_METHOD - for providing alternative RSA implementations
a561f9ff 342\& DSA_METHOD, DH_METHOD, RAND_METHOD, ECDH_METHOD, ECDSA_METHOD,
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343\& STORE_METHOD - similarly for other OpenSSL APIs
344\& EVP_CIPHER - potentially multiple cipher algorithms (indexed by 'nid')
345\& EVP_DIGEST - potentially multiple hash algorithms (indexed by 'nid')
346\& key-loading - loading public and/or private EVP_PKEY keys
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347.Ve
348.Sh "Reference counting and handles"
8b0cefbb 349.IX Subsection "Reference counting and handles"
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350Due to the modular nature of the \s-1ENGINE\s0 \s-1API\s0, pointers to ENGINEs need to be
351treated as handles \- ie. not only as pointers, but also as references to
a561f9ff 352the underlying \s-1ENGINE\s0 object. Ie. one should obtain a new reference when
984263bc 353making copies of an \s-1ENGINE\s0 pointer if the copies will be used (and
aac4ff6f 354released) independently.
984263bc 355.PP
8b0cefbb 356\&\s-1ENGINE\s0 objects have two levels of reference-counting to match the way in
984263bc 357which the objects are used. At the most basic level, each \s-1ENGINE\s0 pointer is
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358inherently a \fBstructural\fR reference \- a structural reference is required
359to use the pointer value at all, as this kind of reference is a guarantee
360that the structure can not be deallocated until the reference is released.
361.PP
362However, a structural reference provides no guarantee that the \s-1ENGINE\s0 is
363initiliased and able to use any of its cryptographic
364implementations. Indeed it's quite possible that most ENGINEs will not
365initialise at all in typical environments, as ENGINEs are typically used to
984263bc 366support specialised hardware. To use an \s-1ENGINE\s0's functionality, you need a
8b0cefbb 367\&\fBfunctional\fR reference. This kind of reference can be considered a
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368specialised form of structural reference, because each functional reference
369implicitly contains a structural reference as well \- however to avoid
370difficult-to-find programming bugs, it is recommended to treat the two
aac4ff6f 371kinds of reference independently. If you have a functional reference to an
8b0cefbb 372\&\s-1ENGINE\s0, you have a guarantee that the \s-1ENGINE\s0 has been initialised ready to
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373perform cryptographic operations and will remain uninitialised
374until after you have released your reference.
984263bc 375.PP
8b0cefbb 376\&\fIStructural references\fR
984263bc 377.PP
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378This basic type of reference is used for instantiating new ENGINEs,
379iterating across OpenSSL's internal linked-list of loaded
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380ENGINEs, reading information about an \s-1ENGINE\s0, etc. Essentially a structural
381reference is sufficient if you only need to query or manipulate the data of
382an \s-1ENGINE\s0 implementation rather than use its functionality.
383.PP
384The \fIENGINE_new()\fR function returns a structural reference to a new (empty)
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385\&\s-1ENGINE\s0 object. There are other \s-1ENGINE\s0 \s-1API\s0 functions that return structural
386references such as; \fIENGINE_by_id()\fR, \fIENGINE_get_first()\fR, \fIENGINE_get_last()\fR,
387\&\fIENGINE_get_next()\fR, \fIENGINE_get_prev()\fR. All structural references should be
388released by a corresponding to call to the \fIENGINE_free()\fR function \- the
389\&\s-1ENGINE\s0 object itself will only actually be cleaned up and deallocated when
390the last structural reference is released.
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391.PP
392It should also be noted that many \s-1ENGINE\s0 \s-1API\s0 function calls that accept a
393structural reference will internally obtain another reference \- typically
394this happens whenever the supplied \s-1ENGINE\s0 will be needed by OpenSSL after
395the function has returned. Eg. the function to add a new \s-1ENGINE\s0 to
396OpenSSL's internal list is \fIENGINE_add()\fR \- if this function returns success,
397then OpenSSL will have stored a new structural reference internally so the
398caller is still responsible for freeing their own reference with
8b0cefbb 399\&\fIENGINE_free()\fR when they are finished with it. In a similar way, some
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400functions will automatically release the structural reference passed to it
401if part of the function's job is to do so. Eg. the \fIENGINE_get_next()\fR and
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402\&\fIENGINE_get_prev()\fR functions are used for iterating across the internal
403\&\s-1ENGINE\s0 list \- they will return a new structural reference to the next (or
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404previous) \s-1ENGINE\s0 in the list or \s-1NULL\s0 if at the end (or beginning) of the
405list, but in either case the structural reference passed to the function is
406released on behalf of the caller.
407.PP
408To clarify a particular function's handling of references, one should
409always consult that function's documentation \*(L"man\*(R" page, or failing that
410the openssl/engine.h header file includes some hints.
411.PP
8b0cefbb 412\&\fIFunctional references\fR
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413.PP
414As mentioned, functional references exist when the cryptographic
415functionality of an \s-1ENGINE\s0 is required to be available. A functional
416reference can be obtained in one of two ways; from an existing structural
417reference to the required \s-1ENGINE\s0, or by asking OpenSSL for the default
418operational \s-1ENGINE\s0 for a given cryptographic purpose.
419.PP
420To obtain a functional reference from an existing structural reference,
421call the \fIENGINE_init()\fR function. This returns zero if the \s-1ENGINE\s0 was not
422already operational and couldn't be successfully initialised (eg. lack of
423system drivers, no special hardware attached, etc), otherwise it will
424return non-zero to indicate that the \s-1ENGINE\s0 is now operational and will
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425have allocated a new \fBfunctional\fR reference to the \s-1ENGINE\s0. All functional
426references are released by calling \fIENGINE_finish()\fR (which removes the
427implicit structural reference as well).
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428.PP
429The second way to get a functional reference is by asking OpenSSL for a
430default implementation for a given task, eg. by \fIENGINE_get_default_RSA()\fR,
8b0cefbb 431\&\fIENGINE_get_default_cipher_engine()\fR, etc. These are discussed in the next
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432section, though they are not usually required by application programmers as
433they are used automatically when creating and using the relevant
434algorithm-specific types in OpenSSL, such as \s-1RSA\s0, \s-1DSA\s0, \s-1EVP_CIPHER_CTX\s0, etc.
435.Sh "Default implementations"
8b0cefbb 436.IX Subsection "Default implementations"
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437For each supported abstraction, the \s-1ENGINE\s0 code maintains an internal table
438of state to control which implementations are available for a given
439abstraction and which should be used by default. These implementations are
a561f9ff 440registered in the tables and indexed by an 'nid' value, because
984263bc 441abstractions like \s-1EVP_CIPHER\s0 and \s-1EVP_DIGEST\s0 support many distinct
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442algorithms and modes, and ENGINEs can support arbitrarily many of them.
443In the case of other abstractions like \s-1RSA\s0, \s-1DSA\s0, etc, there is only one
444\&\*(L"algorithm\*(R" so all implementations implicitly register using the same 'nid'
445index.
446.PP
447When a default \s-1ENGINE\s0 is requested for a given abstraction/algorithm/mode, (eg.
448when calling RSA_new_method(\s-1NULL\s0)), a \*(L"get_default\*(R" call will be made to the
449\&\s-1ENGINE\s0 subsystem to process the corresponding state table and return a
450functional reference to an initialised \s-1ENGINE\s0 whose implementation should be
451used. If no \s-1ENGINE\s0 should (or can) be used, it will return \s-1NULL\s0 and the caller
452will operate with a \s-1NULL\s0 \s-1ENGINE\s0 handle \- this usually equates to using the
453conventional software implementation. In the latter case, OpenSSL will from
454then on behave the way it used to before the \s-1ENGINE\s0 \s-1API\s0 existed.
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455.PP
456Each state table has a flag to note whether it has processed this
8b0cefbb 457\&\*(L"get_default\*(R" query since the table was last modified, because to process
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458this question it must iterate across all the registered ENGINEs in the
459table trying to initialise each of them in turn, in case one of them is
460operational. If it returns a functional reference to an \s-1ENGINE\s0, it will
461also cache another reference to speed up processing future queries (without
462needing to iterate across the table). Likewise, it will cache a \s-1NULL\s0
463response if no \s-1ENGINE\s0 was available so that future queries won't repeat the
464same iteration unless the state table changes. This behaviour can also be
465changed; if the \s-1ENGINE_TABLE_FLAG_NOINIT\s0 flag is set (using
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466\&\fIENGINE_set_table_flags()\fR), no attempted initialisations will take place,
467instead the only way for the state table to return a non-NULL \s-1ENGINE\s0 to the
468\&\*(L"get_default\*(R" query will be if one is expressly set in the table. Eg.
469\&\fIENGINE_set_default_RSA()\fR does the same job as \fIENGINE_register_RSA()\fR except
984263bc 470that it also sets the state table's cached response for the \*(L"get_default\*(R"
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471query. In the case of abstractions like \s-1EVP_CIPHER\s0, where implementations are
472indexed by 'nid', these flags and cached-responses are distinct for each 'nid'
473value.
984263bc 474.Sh "Application requirements"
8b0cefbb 475.IX Subsection "Application requirements"
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476This section will explain the basic things an application programmer should
477support to make the most useful elements of the \s-1ENGINE\s0 functionality
478available to the user. The first thing to consider is whether the
479programmer wishes to make alternative \s-1ENGINE\s0 modules available to the
480application and user. OpenSSL maintains an internal linked list of
aac4ff6f 481\&\*(L"visible\*(R" ENGINEs from which it has to operate \- at start\-up, this list is
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482empty and in fact if an application does not call any \s-1ENGINE\s0 \s-1API\s0 calls and
483it uses static linking against openssl, then the resulting application
484binary will not contain any alternative \s-1ENGINE\s0 code at all. So the first
485consideration is whether any/all available \s-1ENGINE\s0 implementations should be
486made visible to OpenSSL \- this is controlled by calling the various \*(L"load\*(R"
487functions, eg.
488.PP
489.Vb 9
490\& /* Make the "dynamic" ENGINE available */
491\& void ENGINE_load_dynamic(void);
492\& /* Make the CryptoSwift hardware acceleration support available */
493\& void ENGINE_load_cswift(void);
494\& /* Make support for nCipher's "CHIL" hardware available */
495\& void ENGINE_load_chil(void);
496\& ...
497\& /* Make ALL ENGINE implementations bundled with OpenSSL available */
498\& void ENGINE_load_builtin_engines(void);
499.Ve
8b0cefbb 500.PP
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501Having called any of these functions, \s-1ENGINE\s0 objects would have been
502dynamically allocated and populated with these implementations and linked
503into OpenSSL's internal linked list. At this point it is important to
504mention an important \s-1API\s0 function;
505.PP
506.Vb 1
507\& void ENGINE_cleanup(void);
508.Ve
8b0cefbb 509.PP
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510If no \s-1ENGINE\s0 \s-1API\s0 functions are called at all in an application, then there
511are no inherent memory leaks to worry about from the \s-1ENGINE\s0 functionality,
a561f9ff 512however if any ENGINEs are loaded, even if they are never registered or
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513used, it is necessary to use the \fIENGINE_cleanup()\fR function to
514correspondingly cleanup before program exit, if the caller wishes to avoid
515memory leaks. This mechanism uses an internal callback registration table
516so that any \s-1ENGINE\s0 \s-1API\s0 functionality that knows it requires cleanup can
517register its cleanup details to be called during \fIENGINE_cleanup()\fR. This
518approach allows \fIENGINE_cleanup()\fR to clean up after any \s-1ENGINE\s0 functionality
519at all that your program uses, yet doesn't automatically create linker
520dependencies to all possible \s-1ENGINE\s0 functionality \- only the cleanup
521callbacks required by the functionality you do use will be required by the
522linker.
523.PP
524The fact that ENGINEs are made visible to OpenSSL (and thus are linked into
aac4ff6f 525the program and loaded into memory at run\-time) does not mean they are
8b0cefbb 526\&\*(L"registered\*(R" or called into use by OpenSSL automatically \- that behaviour
a561f9ff 527is something for the application to control. Some applications
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528will want to allow the user to specify exactly which \s-1ENGINE\s0 they want used
529if any is to be used at all. Others may prefer to load all support and have
530OpenSSL automatically use at run-time any \s-1ENGINE\s0 that is able to
531successfully initialise \- ie. to assume that this corresponds to
532acceleration hardware attached to the machine or some such thing. There are
533probably numerous other ways in which applications may prefer to handle
534things, so we will simply illustrate the consequences as they apply to a
535couple of simple cases and leave developers to consider these and the
536source code to openssl's builtin utilities as guides.
537.PP
8b0cefbb 538\&\fIUsing a specific \s-1ENGINE\s0 implementation\fR
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539.PP
540Here we'll assume an application has been configured by its user or admin
541to want to use the \*(L"\s-1ACME\s0\*(R" \s-1ENGINE\s0 if it is available in the version of
542OpenSSL the application was compiled with. If it is available, it should be
543used by default for all \s-1RSA\s0, \s-1DSA\s0, and symmetric cipher operation, otherwise
544OpenSSL should use its builtin software as per usual. The following code
545illustrates how to approach this;
546.PP
aac4ff6f 547.Vb 22
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548\& ENGINE *e;
549\& const char *engine_id = "ACME";
550\& ENGINE_load_builtin_engines();
551\& e = ENGINE_by_id(engine_id);
552\& if(!e)
553\& /* the engine isn't available */
554\& return;
555\& if(!ENGINE_init(e)) {
556\& /* the engine couldn't initialise, release 'e' */
557\& ENGINE_free(e);
558\& return;
559\& }
560\& if(!ENGINE_set_default_RSA(e))
561\& /* This should only happen when 'e' can't initialise, but the previous
562\& * statement suggests it did. */
563\& abort();
564\& ENGINE_set_default_DSA(e);
565\& ENGINE_set_default_ciphers(e);
566\& /* Release the functional reference from ENGINE_init() */
567\& ENGINE_finish(e);
568\& /* Release the structural reference from ENGINE_by_id() */
569\& ENGINE_free(e);
570.Ve
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571.PP
572\&\fIAutomatically using builtin \s-1ENGINE\s0 implementations\fR
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573.PP
574Here we'll assume we want to load and register all \s-1ENGINE\s0 implementations
575bundled with OpenSSL, such that for any cryptographic algorithm required by
576OpenSSL \- if there is an \s-1ENGINE\s0 that implements it and can be initialise,
577it should be used. The following code illustrates how this can work;
578.PP
579.Vb 4
580\& /* Load all bundled ENGINEs into memory and make them visible */
581\& ENGINE_load_builtin_engines();
582\& /* Register all of them for every algorithm they collectively implement */
583\& ENGINE_register_all_complete();
584.Ve
8b0cefbb 585.PP
984263bc 586That's all that's required. Eg. the next time OpenSSL tries to set up an
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587\&\s-1RSA\s0 key, any bundled ENGINEs that implement \s-1RSA_METHOD\s0 will be passed to
588\&\fIENGINE_init()\fR and if any of those succeed, that \s-1ENGINE\s0 will be set as the
a561f9ff 589default for \s-1RSA\s0 use from then on.
984263bc 590.Sh "Advanced configuration support"
8b0cefbb 591.IX Subsection "Advanced configuration support"
984263bc 592There is a mechanism supported by the \s-1ENGINE\s0 framework that allows each
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593\&\s-1ENGINE\s0 implementation to define an arbitrary set of configuration
594\&\*(L"commands\*(R" and expose them to OpenSSL and any applications based on
984263bc 595OpenSSL. This mechanism is entirely based on the use of name-value pairs
a561f9ff 596and assumes \s-1ASCII\s0 input (no unicode or \s-1UTF\s0 for now!), so it is ideal if
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597applications want to provide a transparent way for users to provide
598arbitrary configuration \*(L"directives\*(R" directly to such ENGINEs. It is also
599possible for the application to dynamically interrogate the loaded \s-1ENGINE\s0
600implementations for the names, descriptions, and input flags of their
601available \*(L"control commands\*(R", providing a more flexible configuration
602scheme. However, if the user is expected to know which \s-1ENGINE\s0 device he/she
603is using (in the case of specialised hardware, this goes without saying)
604then applications may not need to concern themselves with discovering the
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605supported control commands and simply prefer to pass settings into ENGINEs
606exactly as they are provided by the user.
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607.PP
608Before illustrating how control commands work, it is worth mentioning what
609they are typically used for. Broadly speaking there are two uses for
610control commands; the first is to provide the necessary details to the
611implementation (which may know nothing at all specific to the host system)
612so that it can be initialised for use. This could include the path to any
613driver or config files it needs to load, required network addresses,
a561f9ff 614smart-card identifiers, passwords to initialise protected devices,
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615logging information, etc etc. This class of commands typically needs to be
616passed to an \s-1ENGINE\s0 \fBbefore\fR attempting to initialise it, ie. before
617calling \fIENGINE_init()\fR. The other class of commands consist of settings or
618operations that tweak certain behaviour or cause certain operations to take
619place, and these commands may work either before or after \fIENGINE_init()\fR, or
a561f9ff 620in some cases both. \s-1ENGINE\s0 implementations should provide indications of
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621this in the descriptions attached to builtin control commands and/or in
622external product documentation.
623.PP
8b0cefbb 624\&\fIIssuing control commands to an \s-1ENGINE\s0\fR
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625.PP
626Let's illustrate by example; a function for which the caller supplies the
627name of the \s-1ENGINE\s0 it wishes to use, a table of string-pairs for use before
628initialisation, and another table for use after initialisation. Note that
629the string-pairs used for control commands consist of a command \*(L"name\*(R"
630followed by the command \*(L"parameter\*(R" \- the parameter could be \s-1NULL\s0 in some
631cases but the name can not. This function should initialise the \s-1ENGINE\s0
632(issuing the \*(L"pre\*(R" commands beforehand and the \*(L"post\*(R" commands afterwards)
633and set it as the default for everything except \s-1RAND\s0 and then return a
634boolean success or failure.
635.PP
aac4ff6f 636.Vb 36
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637\& int generic_load_engine_fn(const char *engine_id,
638\& const char **pre_cmds, int pre_num,
639\& const char **post_cmds, int post_num)
640\& {
641\& ENGINE *e = ENGINE_by_id(engine_id);
642\& if(!e) return 0;
aac4ff6f 643\& while(pre_num--) {
984263bc 644\& if(!ENGINE_ctrl_cmd_string(e, pre_cmds[0], pre_cmds[1], 0)) {
aac4ff6f 645\& fprintf(stderr, "Failed command (%s - %s:%s)\en", engine_id,
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646\& pre_cmds[0], pre_cmds[1] ? pre_cmds[1] : "(NULL)");
647\& ENGINE_free(e);
648\& return 0;
649\& }
650\& pre_cmds += 2;
651\& }
652\& if(!ENGINE_init(e)) {
653\& fprintf(stderr, "Failed initialisation\en");
654\& ENGINE_free(e);
655\& return 0;
656\& }
657\& /* ENGINE_init() returned a functional reference, so free the structural
658\& * reference from ENGINE_by_id(). */
659\& ENGINE_free(e);
aac4ff6f 660\& while(post_num--) {
984263bc 661\& if(!ENGINE_ctrl_cmd_string(e, post_cmds[0], post_cmds[1], 0)) {
aac4ff6f 662\& fprintf(stderr, "Failed command (%s - %s:%s)\en", engine_id,
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663\& post_cmds[0], post_cmds[1] ? post_cmds[1] : "(NULL)");
664\& ENGINE_finish(e);
665\& return 0;
666\& }
667\& post_cmds += 2;
668\& }
669\& ENGINE_set_default(e, ENGINE_METHOD_ALL & ~ENGINE_METHOD_RAND);
670\& /* Success */
671\& return 1;
672\& }
673.Ve
8b0cefbb 674.PP
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675Note that \fIENGINE_ctrl_cmd_string()\fR accepts a boolean argument that can
676relax the semantics of the function \- if set non-zero it will only return
677failure if the \s-1ENGINE\s0 supported the given command name but failed while
678executing it, if the \s-1ENGINE\s0 doesn't support the command name it will simply
679return success without doing anything. In this case we assume the user is
680only supplying commands specific to the given \s-1ENGINE\s0 so we set this to
8b0cefbb 681\&\s-1FALSE\s0.
984263bc 682.PP
8b0cefbb 683\&\fIDiscovering supported control commands\fR
984263bc 684.PP
aac4ff6f 685It is possible to discover at run-time the names, numerical\-ids, descriptions
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686and input parameters of the control commands supported by an \s-1ENGINE\s0 using a
687structural reference. Note that some control commands are defined by OpenSSL
688itself and it will intercept and handle these control commands on behalf of the
689\&\s-1ENGINE\s0, ie. the \s-1ENGINE\s0's \fIctrl()\fR handler is not used for the control command.
690openssl/engine.h defines an index, \s-1ENGINE_CMD_BASE\s0, that all control commands
691implemented by ENGINEs should be numbered from. Any command value lower than
692this symbol is considered a \*(L"generic\*(R" command is handled directly by the
693OpenSSL core routines.
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694.PP
695It is using these \*(L"core\*(R" control commands that one can discover the the control
696commands implemented by a given \s-1ENGINE\s0, specifically the commands;
697.PP
698.Vb 9
699\& #define ENGINE_HAS_CTRL_FUNCTION 10
700\& #define ENGINE_CTRL_GET_FIRST_CMD_TYPE 11
701\& #define ENGINE_CTRL_GET_NEXT_CMD_TYPE 12
702\& #define ENGINE_CTRL_GET_CMD_FROM_NAME 13
703\& #define ENGINE_CTRL_GET_NAME_LEN_FROM_CMD 14
704\& #define ENGINE_CTRL_GET_NAME_FROM_CMD 15
705\& #define ENGINE_CTRL_GET_DESC_LEN_FROM_CMD 16
706\& #define ENGINE_CTRL_GET_DESC_FROM_CMD 17
707\& #define ENGINE_CTRL_GET_CMD_FLAGS 18
708.Ve
8b0cefbb 709.PP
984263bc 710Whilst these commands are automatically processed by the OpenSSL framework code,
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711they use various properties exposed by each \s-1ENGINE\s0 to process these
712queries. An \s-1ENGINE\s0 has 3 properties it exposes that can affect how this behaves;
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713it can supply a \fIctrl()\fR handler, it can specify \s-1ENGINE_FLAGS_MANUAL_CMD_CTRL\s0 in
714the \s-1ENGINE\s0's flags, and it can expose an array of control command descriptions.
715If an \s-1ENGINE\s0 specifies the \s-1ENGINE_FLAGS_MANUAL_CMD_CTRL\s0 flag, then it will
716simply pass all these \*(L"core\*(R" control commands directly to the \s-1ENGINE\s0's \fIctrl()\fR
717handler (and thus, it must have supplied one), so it is up to the \s-1ENGINE\s0 to
718reply to these \*(L"discovery\*(R" commands itself. If that flag is not set, then the
719OpenSSL framework code will work with the following rules;
720.PP
721.Vb 9
722\& if no ctrl() handler supplied;
723\& ENGINE_HAS_CTRL_FUNCTION returns FALSE (zero),
724\& all other commands fail.
725\& if a ctrl() handler was supplied but no array of control commands;
726\& ENGINE_HAS_CTRL_FUNCTION returns TRUE,
727\& all other commands fail.
728\& if a ctrl() handler and array of control commands was supplied;
729\& ENGINE_HAS_CTRL_FUNCTION returns TRUE,
730\& all other commands proceed processing ...
731.Ve
8b0cefbb 732.PP
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733If the \s-1ENGINE\s0's array of control commands is empty then all other commands will
734fail, otherwise; \s-1ENGINE_CTRL_GET_FIRST_CMD_TYPE\s0 returns the identifier of
735the first command supported by the \s-1ENGINE\s0, \s-1ENGINE_GET_NEXT_CMD_TYPE\s0 takes the
736identifier of a command supported by the \s-1ENGINE\s0 and returns the next command
737identifier or fails if there are no more, \s-1ENGINE_CMD_FROM_NAME\s0 takes a string
738name for a command and returns the corresponding identifier or fails if no such
739command name exists, and the remaining commands take a command identifier and
740return properties of the corresponding commands. All except
8b0cefbb 741\&\s-1ENGINE_CTRL_GET_FLAGS\s0 return the string length of a command name or description,
984263bc 742or populate a supplied character buffer with a copy of the command name or
aac4ff6f 743description. \s-1ENGINE_CTRL_GET_FLAGS\s0 returns a bitwise\-OR'd mask of the following
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744possible values;
745.PP
746.Vb 4
747\& #define ENGINE_CMD_FLAG_NUMERIC (unsigned int)0x0001
748\& #define ENGINE_CMD_FLAG_STRING (unsigned int)0x0002
749\& #define ENGINE_CMD_FLAG_NO_INPUT (unsigned int)0x0004
750\& #define ENGINE_CMD_FLAG_INTERNAL (unsigned int)0x0008
751.Ve
8b0cefbb 752.PP
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753If the \s-1ENGINE_CMD_FLAG_INTERNAL\s0 flag is set, then any other flags are purely
754informational to the caller \- this flag will prevent the command being usable
755for any higher-level \s-1ENGINE\s0 functions such as \fIENGINE_ctrl_cmd_string()\fR.
8b0cefbb 756\&\*(L"\s-1INTERNAL\s0\*(R" commands are not intended to be exposed to text-based configuration
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757by applications, administrations, users, etc. These can support arbitrary
758operations via \fIENGINE_ctrl()\fR, including passing to and/or from the control
759commands data of any arbitrary type. These commands are supported in the
760discovery mechanisms simply to allow applications determinie if an \s-1ENGINE\s0
761supports certain specific commands it might want to use (eg. application \*(L"foo\*(R"
762might query various ENGINEs to see if they implement \*(L"\s-1FOO_GET_VENDOR_LOGO_GIF\s0\*(R" \-
763and \s-1ENGINE\s0 could therefore decide whether or not to support this \*(L"foo\*(R"\-specific
764extension).
765.Sh "Future developments"
8b0cefbb 766.IX Subsection "Future developments"
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767The \s-1ENGINE\s0 \s-1API\s0 and internal architecture is currently being reviewed. Slated for
768possible release in 0.9.8 is support for transparent loading of \*(L"dynamic\*(R"
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769ENGINEs (built as self-contained shared\-libraries). This would allow \s-1ENGINE\s0
770implementations to be provided independently of OpenSSL libraries and/or
8b0cefbb 771OpenSSL-based applications, and would also remove any requirement for
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772applications to explicitly use the \*(L"dynamic\*(R" \s-1ENGINE\s0 to bind to shared-library
773implementations.
774.SH "SEE ALSO"
74dab6c2 775.IX Header "SEE ALSO"
a561f9ff 776\&\fIrsa\fR\|(3), \fIdsa\fR\|(3), \fIdh\fR\|(3), \fIrand\fR\|(3)