1=pod 2 3=head1 NAME 4 5ENGINE_get_DH, ENGINE_get_DSA, 6ENGINE_by_id, ENGINE_get_cipher_engine, ENGINE_get_default_DH, 7ENGINE_get_default_DSA, 8ENGINE_get_default_RAND, 9ENGINE_get_default_RSA, ENGINE_get_digest_engine, ENGINE_get_first, 10ENGINE_get_last, ENGINE_get_next, ENGINE_get_prev, ENGINE_new, 11ENGINE_get_ciphers, ENGINE_get_ctrl_function, ENGINE_get_digests, 12ENGINE_get_destroy_function, ENGINE_get_finish_function, 13ENGINE_get_init_function, ENGINE_get_load_privkey_function, 14ENGINE_get_load_pubkey_function, ENGINE_load_private_key, 15ENGINE_load_public_key, ENGINE_get_RAND, ENGINE_get_RSA, ENGINE_get_id, 16ENGINE_get_name, ENGINE_get_cmd_defns, ENGINE_get_cipher, 17ENGINE_get_digest, ENGINE_add, ENGINE_cmd_is_executable, 18ENGINE_ctrl, ENGINE_ctrl_cmd, ENGINE_ctrl_cmd_string, 19ENGINE_finish, ENGINE_free, ENGINE_get_flags, ENGINE_init, 20ENGINE_register_DH, ENGINE_register_DSA, 21ENGINE_register_RAND, ENGINE_register_RSA, 22ENGINE_register_all_complete, ENGINE_register_ciphers, 23ENGINE_register_complete, ENGINE_register_digests, ENGINE_remove, 24ENGINE_set_DH, ENGINE_set_DSA, 25ENGINE_set_RAND, ENGINE_set_RSA, ENGINE_set_ciphers, 26ENGINE_set_cmd_defns, ENGINE_set_ctrl_function, ENGINE_set_default, 27ENGINE_set_default_DH, ENGINE_set_default_DSA, 28ENGINE_set_default_RAND, ENGINE_set_default_RSA, 29ENGINE_set_default_ciphers, ENGINE_set_default_digests, 30ENGINE_set_default_string, ENGINE_set_destroy_function, 31ENGINE_set_digests, ENGINE_set_finish_function, ENGINE_set_flags, 32ENGINE_set_id, ENGINE_set_init_function, ENGINE_set_load_privkey_function, 33ENGINE_set_load_pubkey_function, ENGINE_set_name, ENGINE_up_ref, 34ENGINE_get_table_flags, ENGINE_cleanup, 35ENGINE_load_builtin_engines, ENGINE_register_all_DH, 36ENGINE_register_all_DSA, 37ENGINE_register_all_RAND, 38ENGINE_register_all_RSA, ENGINE_register_all_ciphers, 39ENGINE_register_all_digests, ENGINE_set_table_flags, ENGINE_unregister_DH, 40ENGINE_unregister_DSA, 41ENGINE_unregister_RAND, ENGINE_unregister_RSA, ENGINE_unregister_ciphers, 42ENGINE_unregister_digests 43- ENGINE cryptographic module support 44 45=head1 SYNOPSIS 46 47 #include <openssl/engine.h> 48 49 ENGINE *ENGINE_get_first(void); 50 ENGINE *ENGINE_get_last(void); 51 ENGINE *ENGINE_get_next(ENGINE *e); 52 ENGINE *ENGINE_get_prev(ENGINE *e); 53 54 int ENGINE_add(ENGINE *e); 55 int ENGINE_remove(ENGINE *e); 56 57 ENGINE *ENGINE_by_id(const char *id); 58 59 int ENGINE_init(ENGINE *e); 60 int ENGINE_finish(ENGINE *e); 61 62 void ENGINE_load_builtin_engines(void); 63 64 ENGINE *ENGINE_get_default_RSA(void); 65 ENGINE *ENGINE_get_default_DSA(void); 66 ENGINE *ENGINE_get_default_DH(void); 67 ENGINE *ENGINE_get_default_RAND(void); 68 ENGINE *ENGINE_get_cipher_engine(int nid); 69 ENGINE *ENGINE_get_digest_engine(int nid); 70 71 int ENGINE_set_default_RSA(ENGINE *e); 72 int ENGINE_set_default_DSA(ENGINE *e); 73 int ENGINE_set_default_DH(ENGINE *e); 74 int ENGINE_set_default_RAND(ENGINE *e); 75 int ENGINE_set_default_ciphers(ENGINE *e); 76 int ENGINE_set_default_digests(ENGINE *e); 77 int ENGINE_set_default_string(ENGINE *e, const char *list); 78 79 int ENGINE_set_default(ENGINE *e, unsigned int flags); 80 81 unsigned int ENGINE_get_table_flags(void); 82 void ENGINE_set_table_flags(unsigned int flags); 83 84 int ENGINE_register_RSA(ENGINE *e); 85 void ENGINE_unregister_RSA(ENGINE *e); 86 void ENGINE_register_all_RSA(void); 87 int ENGINE_register_DSA(ENGINE *e); 88 void ENGINE_unregister_DSA(ENGINE *e); 89 void ENGINE_register_all_DSA(void); 90 int ENGINE_register_DH(ENGINE *e); 91 void ENGINE_unregister_DH(ENGINE *e); 92 void ENGINE_register_all_DH(void); 93 int ENGINE_register_RAND(ENGINE *e); 94 void ENGINE_unregister_RAND(ENGINE *e); 95 void ENGINE_register_all_RAND(void); 96 int ENGINE_register_ciphers(ENGINE *e); 97 void ENGINE_unregister_ciphers(ENGINE *e); 98 void ENGINE_register_all_ciphers(void); 99 int ENGINE_register_digests(ENGINE *e); 100 void ENGINE_unregister_digests(ENGINE *e); 101 void ENGINE_register_all_digests(void); 102 int ENGINE_register_complete(ENGINE *e); 103 int ENGINE_register_all_complete(void); 104 105 int ENGINE_ctrl(ENGINE *e, int cmd, long i, void *p, void (*f)(void)); 106 int ENGINE_cmd_is_executable(ENGINE *e, int cmd); 107 int ENGINE_ctrl_cmd(ENGINE *e, const char *cmd_name, 108 long i, void *p, void (*f)(void), int cmd_optional); 109 int ENGINE_ctrl_cmd_string(ENGINE *e, const char *cmd_name, const char *arg, 110 int cmd_optional); 111 112 ENGINE *ENGINE_new(void); 113 int ENGINE_free(ENGINE *e); 114 int ENGINE_up_ref(ENGINE *e); 115 116 int ENGINE_set_id(ENGINE *e, const char *id); 117 int ENGINE_set_name(ENGINE *e, const char *name); 118 int ENGINE_set_RSA(ENGINE *e, const RSA_METHOD *rsa_meth); 119 int ENGINE_set_DSA(ENGINE *e, const DSA_METHOD *dsa_meth); 120 int ENGINE_set_DH(ENGINE *e, const DH_METHOD *dh_meth); 121 int ENGINE_set_RAND(ENGINE *e, const RAND_METHOD *rand_meth); 122 int ENGINE_set_destroy_function(ENGINE *e, ENGINE_GEN_INT_FUNC_PTR destroy_f); 123 int ENGINE_set_init_function(ENGINE *e, ENGINE_GEN_INT_FUNC_PTR init_f); 124 int ENGINE_set_finish_function(ENGINE *e, ENGINE_GEN_INT_FUNC_PTR finish_f); 125 int ENGINE_set_ctrl_function(ENGINE *e, ENGINE_CTRL_FUNC_PTR ctrl_f); 126 int ENGINE_set_load_privkey_function(ENGINE *e, ENGINE_LOAD_KEY_PTR loadpriv_f); 127 int ENGINE_set_load_pubkey_function(ENGINE *e, ENGINE_LOAD_KEY_PTR loadpub_f); 128 int ENGINE_set_ciphers(ENGINE *e, ENGINE_CIPHERS_PTR f); 129 int ENGINE_set_digests(ENGINE *e, ENGINE_DIGESTS_PTR f); 130 int ENGINE_set_flags(ENGINE *e, int flags); 131 int ENGINE_set_cmd_defns(ENGINE *e, const ENGINE_CMD_DEFN *defns); 132 133 const char *ENGINE_get_id(const ENGINE *e); 134 const char *ENGINE_get_name(const ENGINE *e); 135 const RSA_METHOD *ENGINE_get_RSA(const ENGINE *e); 136 const DSA_METHOD *ENGINE_get_DSA(const ENGINE *e); 137 const DH_METHOD *ENGINE_get_DH(const ENGINE *e); 138 const RAND_METHOD *ENGINE_get_RAND(const ENGINE *e); 139 ENGINE_GEN_INT_FUNC_PTR ENGINE_get_destroy_function(const ENGINE *e); 140 ENGINE_GEN_INT_FUNC_PTR ENGINE_get_init_function(const ENGINE *e); 141 ENGINE_GEN_INT_FUNC_PTR ENGINE_get_finish_function(const ENGINE *e); 142 ENGINE_CTRL_FUNC_PTR ENGINE_get_ctrl_function(const ENGINE *e); 143 ENGINE_LOAD_KEY_PTR ENGINE_get_load_privkey_function(const ENGINE *e); 144 ENGINE_LOAD_KEY_PTR ENGINE_get_load_pubkey_function(const ENGINE *e); 145 ENGINE_CIPHERS_PTR ENGINE_get_ciphers(const ENGINE *e); 146 ENGINE_DIGESTS_PTR ENGINE_get_digests(const ENGINE *e); 147 const EVP_CIPHER *ENGINE_get_cipher(ENGINE *e, int nid); 148 const EVP_MD *ENGINE_get_digest(ENGINE *e, int nid); 149 int ENGINE_get_flags(const ENGINE *e); 150 const ENGINE_CMD_DEFN *ENGINE_get_cmd_defns(const ENGINE *e); 151 152 EVP_PKEY *ENGINE_load_private_key(ENGINE *e, const char *key_id, 153 UI_METHOD *ui_method, void *callback_data); 154 EVP_PKEY *ENGINE_load_public_key(ENGINE *e, const char *key_id, 155 UI_METHOD *ui_method, void *callback_data); 156 157Deprecated: 158 159 #if OPENSSL_API_COMPAT < 0x10100000L 160 void ENGINE_cleanup(void) 161 #endif 162 163=head1 DESCRIPTION 164 165These functions create, manipulate, and use cryptographic modules in the 166form of B<ENGINE> objects. These objects act as containers for 167implementations of cryptographic algorithms, and support a 168reference-counted mechanism to allow them to be dynamically loaded in and 169out of the running application. 170 171The cryptographic functionality that can be provided by an B<ENGINE> 172implementation includes the following abstractions; 173 174 RSA_METHOD - for providing alternative RSA implementations 175 DSA_METHOD, DH_METHOD, RAND_METHOD, ECDH_METHOD, ECDSA_METHOD, 176 - similarly for other OpenSSL APIs 177 EVP_CIPHER - potentially multiple cipher algorithms (indexed by 'nid') 178 EVP_DIGEST - potentially multiple hash algorithms (indexed by 'nid') 179 key-loading - loading public and/or private EVP_PKEY keys 180 181=head2 Reference counting and handles 182 183Due to the modular nature of the ENGINE API, pointers to ENGINEs need to be 184treated as handles - i.e. not only as pointers, but also as references to 185the underlying ENGINE object. Ie. one should obtain a new reference when 186making copies of an ENGINE pointer if the copies will be used (and 187released) independently. 188 189ENGINE objects have two levels of reference-counting to match the way in 190which the objects are used. At the most basic level, each ENGINE pointer is 191inherently a B<structural> reference - a structural reference is required 192to use the pointer value at all, as this kind of reference is a guarantee 193that the structure can not be deallocated until the reference is released. 194 195However, a structural reference provides no guarantee that the ENGINE is 196initialised and able to use any of its cryptographic 197implementations. Indeed it's quite possible that most ENGINEs will not 198initialise at all in typical environments, as ENGINEs are typically used to 199support specialised hardware. To use an ENGINE's functionality, you need a 200B<functional> reference. This kind of reference can be considered a 201specialised form of structural reference, because each functional reference 202implicitly contains a structural reference as well - however to avoid 203difficult-to-find programming bugs, it is recommended to treat the two 204kinds of reference independently. If you have a functional reference to an 205ENGINE, you have a guarantee that the ENGINE has been initialised and 206is ready to perform cryptographic operations, and will remain initialised 207until after you have released your reference. 208 209I<Structural references> 210 211This basic type of reference is used for instantiating new ENGINEs, 212iterating across OpenSSL's internal linked-list of loaded 213ENGINEs, reading information about an ENGINE, etc. Essentially a structural 214reference is sufficient if you only need to query or manipulate the data of 215an ENGINE implementation rather than use its functionality. 216 217The ENGINE_new() function returns a structural reference to a new (empty) 218ENGINE object. There are other ENGINE API functions that return structural 219references such as; ENGINE_by_id(), ENGINE_get_first(), ENGINE_get_last(), 220ENGINE_get_next(), ENGINE_get_prev(). All structural references should be 221released by a corresponding to call to the ENGINE_free() function - the 222ENGINE object itself will only actually be cleaned up and deallocated when 223the last structural reference is released. 224 225It should also be noted that many ENGINE API function calls that accept a 226structural reference will internally obtain another reference - typically 227this happens whenever the supplied ENGINE will be needed by OpenSSL after 228the function has returned. Eg. the function to add a new ENGINE to 229OpenSSL's internal list is ENGINE_add() - if this function returns success, 230then OpenSSL will have stored a new structural reference internally so the 231caller is still responsible for freeing their own reference with 232ENGINE_free() when they are finished with it. In a similar way, some 233functions will automatically release the structural reference passed to it 234if part of the function's job is to do so. Eg. the ENGINE_get_next() and 235ENGINE_get_prev() functions are used for iterating across the internal 236ENGINE list - they will return a new structural reference to the next (or 237previous) ENGINE in the list or NULL if at the end (or beginning) of the 238list, but in either case the structural reference passed to the function is 239released on behalf of the caller. 240 241To clarify a particular function's handling of references, one should 242always consult that function's documentation "man" page, or failing that 243the openssl/engine.h header file includes some hints. 244 245I<Functional references> 246 247As mentioned, functional references exist when the cryptographic 248functionality of an ENGINE is required to be available. A functional 249reference can be obtained in one of two ways; from an existing structural 250reference to the required ENGINE, or by asking OpenSSL for the default 251operational ENGINE for a given cryptographic purpose. 252 253To obtain a functional reference from an existing structural reference, 254call the ENGINE_init() function. This returns zero if the ENGINE was not 255already operational and couldn't be successfully initialised (e.g. lack of 256system drivers, no special hardware attached, etc), otherwise it will 257return nonzero to indicate that the ENGINE is now operational and will 258have allocated a new B<functional> reference to the ENGINE. All functional 259references are released by calling ENGINE_finish() (which removes the 260implicit structural reference as well). 261 262The second way to get a functional reference is by asking OpenSSL for a 263default implementation for a given task, e.g. by ENGINE_get_default_RSA(), 264ENGINE_get_default_cipher_engine(), etc. These are discussed in the next 265section, though they are not usually required by application programmers as 266they are used automatically when creating and using the relevant 267algorithm-specific types in OpenSSL, such as RSA, DSA, EVP_CIPHER_CTX, etc. 268 269=head2 Default implementations 270 271For each supported abstraction, the ENGINE code maintains an internal table 272of state to control which implementations are available for a given 273abstraction and which should be used by default. These implementations are 274registered in the tables and indexed by an 'nid' value, because 275abstractions like EVP_CIPHER and EVP_DIGEST support many distinct 276algorithms and modes, and ENGINEs can support arbitrarily many of them. 277In the case of other abstractions like RSA, DSA, etc, there is only one 278"algorithm" so all implementations implicitly register using the same 'nid' 279index. 280 281When a default ENGINE is requested for a given abstraction/algorithm/mode, (e.g. 282when calling RSA_new_method(NULL)), a "get_default" call will be made to the 283ENGINE subsystem to process the corresponding state table and return a 284functional reference to an initialised ENGINE whose implementation should be 285used. If no ENGINE should (or can) be used, it will return NULL and the caller 286will operate with a NULL ENGINE handle - this usually equates to using the 287conventional software implementation. In the latter case, OpenSSL will from 288then on behave the way it used to before the ENGINE API existed. 289 290Each state table has a flag to note whether it has processed this 291"get_default" query since the table was last modified, because to process 292this question it must iterate across all the registered ENGINEs in the 293table trying to initialise each of them in turn, in case one of them is 294operational. If it returns a functional reference to an ENGINE, it will 295also cache another reference to speed up processing future queries (without 296needing to iterate across the table). Likewise, it will cache a NULL 297response if no ENGINE was available so that future queries won't repeat the 298same iteration unless the state table changes. This behaviour can also be 299changed; if the ENGINE_TABLE_FLAG_NOINIT flag is set (using 300ENGINE_set_table_flags()), no attempted initialisations will take place, 301instead the only way for the state table to return a non-NULL ENGINE to the 302"get_default" query will be if one is expressly set in the table. Eg. 303ENGINE_set_default_RSA() does the same job as ENGINE_register_RSA() except 304that it also sets the state table's cached response for the "get_default" 305query. In the case of abstractions like EVP_CIPHER, where implementations are 306indexed by 'nid', these flags and cached-responses are distinct for each 'nid' 307value. 308 309=head2 Application requirements 310 311This section will explain the basic things an application programmer should 312support to make the most useful elements of the ENGINE functionality 313available to the user. The first thing to consider is whether the 314programmer wishes to make alternative ENGINE modules available to the 315application and user. OpenSSL maintains an internal linked list of 316"visible" ENGINEs from which it has to operate - at start-up, this list is 317empty and in fact if an application does not call any ENGINE API calls and 318it uses static linking against openssl, then the resulting application 319binary will not contain any alternative ENGINE code at all. So the first 320consideration is whether any/all available ENGINE implementations should be 321made visible to OpenSSL - this is controlled by calling the various "load" 322functions. 323 324The fact that ENGINEs are made visible to OpenSSL (and thus are linked into 325the program and loaded into memory at run-time) does not mean they are 326"registered" or called into use by OpenSSL automatically - that behaviour 327is something for the application to control. Some applications 328will want to allow the user to specify exactly which ENGINE they want used 329if any is to be used at all. Others may prefer to load all support and have 330OpenSSL automatically use at run-time any ENGINE that is able to 331successfully initialise - i.e. to assume that this corresponds to 332acceleration hardware attached to the machine or some such thing. There are 333probably numerous other ways in which applications may prefer to handle 334things, so we will simply illustrate the consequences as they apply to a 335couple of simple cases and leave developers to consider these and the 336source code to openssl's builtin utilities as guides. 337 338If no ENGINE API functions are called within an application, then OpenSSL 339will not allocate any internal resources. Prior to OpenSSL 1.1.0, however, 340if any ENGINEs are loaded, even if not registered or used, it was necessary to 341call ENGINE_cleanup() before the program exits. 342 343I<Using a specific ENGINE implementation> 344 345Here we'll assume an application has been configured by its user or admin 346to want to use the "ACME" ENGINE if it is available in the version of 347OpenSSL the application was compiled with. If it is available, it should be 348used by default for all RSA, DSA, and symmetric cipher operations, otherwise 349OpenSSL should use its builtin software as per usual. The following code 350illustrates how to approach this; 351 352 ENGINE *e; 353 const char *engine_id = "ACME"; 354 ENGINE_load_builtin_engines(); 355 e = ENGINE_by_id(engine_id); 356 if (!e) 357 /* the engine isn't available */ 358 return; 359 if (!ENGINE_init(e)) { 360 /* the engine couldn't initialise, release 'e' */ 361 ENGINE_free(e); 362 return; 363 } 364 if (!ENGINE_set_default_RSA(e)) 365 /* 366 * This should only happen when 'e' can't initialise, but the previous 367 * statement suggests it did. 368 */ 369 abort(); 370 ENGINE_set_default_DSA(e); 371 ENGINE_set_default_ciphers(e); 372 /* Release the functional reference from ENGINE_init() */ 373 ENGINE_finish(e); 374 /* Release the structural reference from ENGINE_by_id() */ 375 ENGINE_free(e); 376 377I<Automatically using builtin ENGINE implementations> 378 379Here we'll assume we want to load and register all ENGINE implementations 380bundled with OpenSSL, such that for any cryptographic algorithm required by 381OpenSSL - if there is an ENGINE that implements it and can be initialised, 382it should be used. The following code illustrates how this can work; 383 384 /* Load all bundled ENGINEs into memory and make them visible */ 385 ENGINE_load_builtin_engines(); 386 /* Register all of them for every algorithm they collectively implement */ 387 ENGINE_register_all_complete(); 388 389That's all that's required. Eg. the next time OpenSSL tries to set up an 390RSA key, any bundled ENGINEs that implement RSA_METHOD will be passed to 391ENGINE_init() and if any of those succeed, that ENGINE will be set as the 392default for RSA use from then on. 393 394=head2 Advanced configuration support 395 396There is a mechanism supported by the ENGINE framework that allows each 397ENGINE implementation to define an arbitrary set of configuration 398"commands" and expose them to OpenSSL and any applications based on 399OpenSSL. This mechanism is entirely based on the use of name-value pairs 400and assumes ASCII input (no unicode or UTF for now!), so it is ideal if 401applications want to provide a transparent way for users to provide 402arbitrary configuration "directives" directly to such ENGINEs. It is also 403possible for the application to dynamically interrogate the loaded ENGINE 404implementations for the names, descriptions, and input flags of their 405available "control commands", providing a more flexible configuration 406scheme. However, if the user is expected to know which ENGINE device he/she 407is using (in the case of specialised hardware, this goes without saying) 408then applications may not need to concern themselves with discovering the 409supported control commands and simply prefer to pass settings into ENGINEs 410exactly as they are provided by the user. 411 412Before illustrating how control commands work, it is worth mentioning what 413they are typically used for. Broadly speaking there are two uses for 414control commands; the first is to provide the necessary details to the 415implementation (which may know nothing at all specific to the host system) 416so that it can be initialised for use. This could include the path to any 417driver or config files it needs to load, required network addresses, 418smart-card identifiers, passwords to initialise protected devices, 419logging information, etc etc. This class of commands typically needs to be 420passed to an ENGINE B<before> attempting to initialise it, i.e. before 421calling ENGINE_init(). The other class of commands consist of settings or 422operations that tweak certain behaviour or cause certain operations to take 423place, and these commands may work either before or after ENGINE_init(), or 424in some cases both. ENGINE implementations should provide indications of 425this in the descriptions attached to builtin control commands and/or in 426external product documentation. 427 428I<Issuing control commands to an ENGINE> 429 430Let's illustrate by example; a function for which the caller supplies the 431name of the ENGINE it wishes to use, a table of string-pairs for use before 432initialisation, and another table for use after initialisation. Note that 433the string-pairs used for control commands consist of a command "name" 434followed by the command "parameter" - the parameter could be NULL in some 435cases but the name can not. This function should initialise the ENGINE 436(issuing the "pre" commands beforehand and the "post" commands afterwards) 437and set it as the default for everything except RAND and then return a 438boolean success or failure. 439 440 int generic_load_engine_fn(const char *engine_id, 441 const char **pre_cmds, int pre_num, 442 const char **post_cmds, int post_num) 443 { 444 ENGINE *e = ENGINE_by_id(engine_id); 445 if (!e) return 0; 446 while (pre_num--) { 447 if (!ENGINE_ctrl_cmd_string(e, pre_cmds[0], pre_cmds[1], 0)) { 448 fprintf(stderr, "Failed command (%s - %s:%s)\n", engine_id, 449 pre_cmds[0], pre_cmds[1] ? pre_cmds[1] : "(NULL)"); 450 ENGINE_free(e); 451 return 0; 452 } 453 pre_cmds += 2; 454 } 455 if (!ENGINE_init(e)) { 456 fprintf(stderr, "Failed initialisation\n"); 457 ENGINE_free(e); 458 return 0; 459 } 460 /* 461 * ENGINE_init() returned a functional reference, so free the structural 462 * reference from ENGINE_by_id(). 463 */ 464 ENGINE_free(e); 465 while (post_num--) { 466 if (!ENGINE_ctrl_cmd_string(e, post_cmds[0], post_cmds[1], 0)) { 467 fprintf(stderr, "Failed command (%s - %s:%s)\n", engine_id, 468 post_cmds[0], post_cmds[1] ? post_cmds[1] : "(NULL)"); 469 ENGINE_finish(e); 470 return 0; 471 } 472 post_cmds += 2; 473 } 474 ENGINE_set_default(e, ENGINE_METHOD_ALL & ~ENGINE_METHOD_RAND); 475 /* Success */ 476 return 1; 477 } 478 479Note that ENGINE_ctrl_cmd_string() accepts a boolean argument that can 480relax the semantics of the function - if set nonzero it will only return 481failure if the ENGINE supported the given command name but failed while 482executing it, if the ENGINE doesn't support the command name it will simply 483return success without doing anything. In this case we assume the user is 484only supplying commands specific to the given ENGINE so we set this to 485FALSE. 486 487I<Discovering supported control commands> 488 489It is possible to discover at run-time the names, numerical-ids, descriptions 490and input parameters of the control commands supported by an ENGINE using a 491structural reference. Note that some control commands are defined by OpenSSL 492itself and it will intercept and handle these control commands on behalf of the 493ENGINE, i.e. the ENGINE's ctrl() handler is not used for the control command. 494openssl/engine.h defines an index, ENGINE_CMD_BASE, that all control commands 495implemented by ENGINEs should be numbered from. Any command value lower than 496this symbol is considered a "generic" command is handled directly by the 497OpenSSL core routines. 498 499It is using these "core" control commands that one can discover the control 500commands implemented by a given ENGINE, specifically the commands: 501 502 ENGINE_HAS_CTRL_FUNCTION 503 ENGINE_CTRL_GET_FIRST_CMD_TYPE 504 ENGINE_CTRL_GET_NEXT_CMD_TYPE 505 ENGINE_CTRL_GET_CMD_FROM_NAME 506 ENGINE_CTRL_GET_NAME_LEN_FROM_CMD 507 ENGINE_CTRL_GET_NAME_FROM_CMD 508 ENGINE_CTRL_GET_DESC_LEN_FROM_CMD 509 ENGINE_CTRL_GET_DESC_FROM_CMD 510 ENGINE_CTRL_GET_CMD_FLAGS 511 512Whilst these commands are automatically processed by the OpenSSL framework code, 513they use various properties exposed by each ENGINE to process these 514queries. An ENGINE has 3 properties it exposes that can affect how this behaves; 515it can supply a ctrl() handler, it can specify ENGINE_FLAGS_MANUAL_CMD_CTRL in 516the ENGINE's flags, and it can expose an array of control command descriptions. 517If an ENGINE specifies the ENGINE_FLAGS_MANUAL_CMD_CTRL flag, then it will 518simply pass all these "core" control commands directly to the ENGINE's ctrl() 519handler (and thus, it must have supplied one), so it is up to the ENGINE to 520reply to these "discovery" commands itself. If that flag is not set, then the 521OpenSSL framework code will work with the following rules: 522 523 if no ctrl() handler supplied; 524 ENGINE_HAS_CTRL_FUNCTION returns FALSE (zero), 525 all other commands fail. 526 if a ctrl() handler was supplied but no array of control commands; 527 ENGINE_HAS_CTRL_FUNCTION returns TRUE, 528 all other commands fail. 529 if a ctrl() handler and array of control commands was supplied; 530 ENGINE_HAS_CTRL_FUNCTION returns TRUE, 531 all other commands proceed processing ... 532 533If the ENGINE's array of control commands is empty then all other commands will 534fail, otherwise; ENGINE_CTRL_GET_FIRST_CMD_TYPE returns the identifier of 535the first command supported by the ENGINE, ENGINE_GET_NEXT_CMD_TYPE takes the 536identifier of a command supported by the ENGINE and returns the next command 537identifier or fails if there are no more, ENGINE_CMD_FROM_NAME takes a string 538name for a command and returns the corresponding identifier or fails if no such 539command name exists, and the remaining commands take a command identifier and 540return properties of the corresponding commands. All except 541ENGINE_CTRL_GET_FLAGS return the string length of a command name or description, 542or populate a supplied character buffer with a copy of the command name or 543description. ENGINE_CTRL_GET_FLAGS returns a bitwise-OR'd mask of the following 544possible values: 545 546 ENGINE_CMD_FLAG_NUMERIC 547 ENGINE_CMD_FLAG_STRING 548 ENGINE_CMD_FLAG_NO_INPUT 549 ENGINE_CMD_FLAG_INTERNAL 550 551If the ENGINE_CMD_FLAG_INTERNAL flag is set, then any other flags are purely 552informational to the caller - this flag will prevent the command being usable 553for any higher-level ENGINE functions such as ENGINE_ctrl_cmd_string(). 554"INTERNAL" commands are not intended to be exposed to text-based configuration 555by applications, administrations, users, etc. These can support arbitrary 556operations via ENGINE_ctrl(), including passing to and/or from the control 557commands data of any arbitrary type. These commands are supported in the 558discovery mechanisms simply to allow applications to determine if an ENGINE 559supports certain specific commands it might want to use (e.g. application "foo" 560might query various ENGINEs to see if they implement "FOO_GET_VENDOR_LOGO_GIF" - 561and ENGINE could therefore decide whether or not to support this "foo"-specific 562extension). 563 564=head1 ENVIRONMENT 565 566=over 4 567 568=item B<OPENSSL_ENGINES> 569 570The path to the engines directory. 571Ignored in set-user-ID and set-group-ID programs. 572 573=back 574 575=head1 RETURN VALUES 576 577ENGINE_get_first(), ENGINE_get_last(), ENGINE_get_next() and ENGINE_get_prev() 578return a valid B<ENGINE> structure or NULL if an error occurred. 579 580ENGINE_add() and ENGINE_remove() return 1 on success or 0 on error. 581 582ENGINE_by_id() returns a valid B<ENGINE> structure or NULL if an error occurred. 583 584ENGINE_init() and ENGINE_finish() return 1 on success or 0 on error. 585 586All ENGINE_get_default_TYPE() functions, ENGINE_get_cipher_engine() and 587ENGINE_get_digest_engine() return a valid B<ENGINE> structure on success or NULL 588if an error occurred. 589 590All ENGINE_set_default_TYPE() functions return 1 on success or 0 on error. 591 592ENGINE_set_default() returns 1 on success or 0 on error. 593 594ENGINE_get_table_flags() returns an unsigned integer value representing the 595global table flags which are used to control the registration behaviour of 596B<ENGINE> implementations. 597 598All ENGINE_register_TYPE() functions return 1 on success or 0 on error. 599 600ENGINE_register_complete() and ENGINE_register_all_complete() always return 1. 601 602ENGINE_ctrl() returns a positive value on success or others on error. 603 604ENGINE_cmd_is_executable() returns 1 if B<cmd> is executable or 0 otherwise. 605 606ENGINE_ctrl_cmd() and ENGINE_ctrl_cmd_string() return 1 on success or 0 on error. 607 608ENGINE_new() returns a valid B<ENGINE> structure on success or NULL if an error 609occurred. 610 611ENGINE_free() always returns 1. 612 613ENGINE_up_ref() returns 1 on success or 0 on error. 614 615ENGINE_set_id() and ENGINE_set_name() return 1 on success or 0 on error. 616 617All other B<ENGINE_set_*> functions return 1 on success or 0 on error. 618 619ENGINE_get_id() and ENGINE_get_name() return a string representing the identifier 620and the name of the ENGINE B<e> respectively. 621 622ENGINE_get_RSA(), ENGINE_get_DSA(), ENGINE_get_DH() and ENGINE_get_RAND() 623return corresponding method structures for each algorithms. 624 625ENGINE_get_destroy_function(), ENGINE_get_init_function(), 626ENGINE_get_finish_function(), ENGINE_get_ctrl_function(), 627ENGINE_get_load_privkey_function(), ENGINE_get_load_pubkey_function(), 628ENGINE_get_ciphers() and ENGINE_get_digests() return corresponding function 629pointers of the callbacks. 630 631ENGINE_get_cipher() returns a valid B<EVP_CIPHER> structure on success or NULL 632if an error occurred. 633 634ENGINE_get_digest() returns a valid B<EVP_MD> structure on success or NULL if an 635error occurred. 636 637ENGINE_get_flags() returns an integer representing the ENGINE flags which are 638used to control various behaviours of an ENGINE. 639 640ENGINE_get_cmd_defns() returns an B<ENGINE_CMD_DEFN> structure or NULL if it's 641not set. 642 643ENGINE_load_private_key() and ENGINE_load_public_key() return a valid B<EVP_PKEY> 644structure on success or NULL if an error occurred. 645 646=head1 SEE ALSO 647 648L<OPENSSL_init_crypto(3)>, L<RSA_new_method(3)>, L<DSA_new(3)>, L<DH_new(3)>, 649L<RAND_bytes(3)>, L<config(5)> 650 651=head1 HISTORY 652 653ENGINE_cleanup() was deprecated in OpenSSL 1.1.0 by the automatic cleanup 654done by OPENSSL_cleanup() 655and should not be used. 656 657=head1 COPYRIGHT 658 659Copyright 2002-2021 The OpenSSL Project Authors. All Rights Reserved. 660 661Licensed under the OpenSSL license (the "License"). You may not use 662this file except in compliance with the License. You can obtain a copy 663in the file LICENSE in the source distribution or at 664L<https://www.openssl.org/source/license.html>. 665 666=cut 667