1=pod 2 3=head1 NAME 4 5engine - 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); 26 #ifndef OPENSSL_NO_STATIC_ENGINE 27 void ENGINE_load_4758cca(void); 28 void ENGINE_load_aep(void); 29 void ENGINE_load_atalla(void); 30 void ENGINE_load_chil(void); 31 void ENGINE_load_cswift(void); 32 void ENGINE_load_gmp(void); 33 void ENGINE_load_nuron(void); 34 void ENGINE_load_sureware(void); 35 void ENGINE_load_ubsec(void); 36 #endif 37 void ENGINE_load_cryptodev(void); 38 void ENGINE_load_builtin_engines(void); 39 40 void ENGINE_cleanup(void); 41 42 ENGINE *ENGINE_get_default_RSA(void); 43 ENGINE *ENGINE_get_default_DSA(void); 44 ENGINE *ENGINE_get_default_ECDH(void); 45 ENGINE *ENGINE_get_default_ECDSA(void); 46 ENGINE *ENGINE_get_default_DH(void); 47 ENGINE *ENGINE_get_default_RAND(void); 48 ENGINE *ENGINE_get_cipher_engine(int nid); 49 ENGINE *ENGINE_get_digest_engine(int nid); 50 51 int ENGINE_set_default_RSA(ENGINE *e); 52 int ENGINE_set_default_DSA(ENGINE *e); 53 int ENGINE_set_default_ECDH(ENGINE *e); 54 int ENGINE_set_default_ECDSA(ENGINE *e); 55 int ENGINE_set_default_DH(ENGINE *e); 56 int ENGINE_set_default_RAND(ENGINE *e); 57 int ENGINE_set_default_ciphers(ENGINE *e); 58 int ENGINE_set_default_digests(ENGINE *e); 59 int ENGINE_set_default_string(ENGINE *e, const char *list); 60 61 int ENGINE_set_default(ENGINE *e, unsigned int flags); 62 63 unsigned int ENGINE_get_table_flags(void); 64 void ENGINE_set_table_flags(unsigned int flags); 65 66 int ENGINE_register_RSA(ENGINE *e); 67 void ENGINE_unregister_RSA(ENGINE *e); 68 void ENGINE_register_all_RSA(void); 69 int ENGINE_register_DSA(ENGINE *e); 70 void ENGINE_unregister_DSA(ENGINE *e); 71 void ENGINE_register_all_DSA(void); 72 int ENGINE_register_ECDH(ENGINE *e); 73 void ENGINE_unregister_ECDH(ENGINE *e); 74 void ENGINE_register_all_ECDH(void); 75 int ENGINE_register_ECDSA(ENGINE *e); 76 void ENGINE_unregister_ECDSA(ENGINE *e); 77 void ENGINE_register_all_ECDSA(void); 78 int ENGINE_register_DH(ENGINE *e); 79 void ENGINE_unregister_DH(ENGINE *e); 80 void ENGINE_register_all_DH(void); 81 int ENGINE_register_RAND(ENGINE *e); 82 void ENGINE_unregister_RAND(ENGINE *e); 83 void ENGINE_register_all_RAND(void); 84 int ENGINE_register_STORE(ENGINE *e); 85 void ENGINE_unregister_STORE(ENGINE *e); 86 void ENGINE_register_all_STORE(void); 87 int ENGINE_register_ciphers(ENGINE *e); 88 void ENGINE_unregister_ciphers(ENGINE *e); 89 void ENGINE_register_all_ciphers(void); 90 int ENGINE_register_digests(ENGINE *e); 91 void ENGINE_unregister_digests(ENGINE *e); 92 void ENGINE_register_all_digests(void); 93 int ENGINE_register_complete(ENGINE *e); 94 int ENGINE_register_all_complete(void); 95 96 int ENGINE_ctrl(ENGINE *e, int cmd, long i, void *p, void (*f)(void)); 97 int ENGINE_cmd_is_executable(ENGINE *e, int cmd); 98 int ENGINE_ctrl_cmd(ENGINE *e, const char *cmd_name, 99 long i, void *p, void (*f)(void), int cmd_optional); 100 int ENGINE_ctrl_cmd_string(ENGINE *e, const char *cmd_name, const char *arg, 101 int cmd_optional); 102 103 int ENGINE_set_ex_data(ENGINE *e, int idx, void *arg); 104 void *ENGINE_get_ex_data(const ENGINE *e, int idx); 105 106 int ENGINE_get_ex_new_index(long argl, void *argp, CRYPTO_EX_new *new_func, 107 CRYPTO_EX_dup *dup_func, CRYPTO_EX_free *free_func); 108 109 ENGINE *ENGINE_new(void); 110 int ENGINE_free(ENGINE *e); 111 int ENGINE_up_ref(ENGINE *e); 112 113 int ENGINE_set_id(ENGINE *e, const char *id); 114 int ENGINE_set_name(ENGINE *e, const char *name); 115 int ENGINE_set_RSA(ENGINE *e, const RSA_METHOD *rsa_meth); 116 int ENGINE_set_DSA(ENGINE *e, const DSA_METHOD *dsa_meth); 117 int ENGINE_set_ECDH(ENGINE *e, const ECDH_METHOD *dh_meth); 118 int ENGINE_set_ECDSA(ENGINE *e, const ECDSA_METHOD *dh_meth); 119 int ENGINE_set_DH(ENGINE *e, const DH_METHOD *dh_meth); 120 int ENGINE_set_RAND(ENGINE *e, const RAND_METHOD *rand_meth); 121 int ENGINE_set_STORE(ENGINE *e, const STORE_METHOD *rand_meth); 122 int ENGINE_set_destroy_function(ENGINE *e, ENGINE_GEN_INT_FUNC_PTR destroy_f); 123 int ENGINE_set_init_function(ENGINE *e, ENGINE_GEN_INT_FUNC_PTR init_f); 124 int ENGINE_set_finish_function(ENGINE *e, ENGINE_GEN_INT_FUNC_PTR finish_f); 125 int ENGINE_set_ctrl_function(ENGINE *e, ENGINE_CTRL_FUNC_PTR ctrl_f); 126 int ENGINE_set_load_privkey_function(ENGINE *e, ENGINE_LOAD_KEY_PTR loadpriv_f); 127 int ENGINE_set_load_pubkey_function(ENGINE *e, ENGINE_LOAD_KEY_PTR loadpub_f); 128 int ENGINE_set_ciphers(ENGINE *e, ENGINE_CIPHERS_PTR f); 129 int ENGINE_set_digests(ENGINE *e, ENGINE_DIGESTS_PTR f); 130 int ENGINE_set_flags(ENGINE *e, int flags); 131 int ENGINE_set_cmd_defns(ENGINE *e, const ENGINE_CMD_DEFN *defns); 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 ECDH_METHOD *ENGINE_get_ECDH(const ENGINE *e); 138 const ECDSA_METHOD *ENGINE_get_ECDSA(const ENGINE *e); 139 const DH_METHOD *ENGINE_get_DH(const ENGINE *e); 140 const RAND_METHOD *ENGINE_get_RAND(const ENGINE *e); 141 const STORE_METHOD *ENGINE_get_STORE(const ENGINE *e); 142 ENGINE_GEN_INT_FUNC_PTR ENGINE_get_destroy_function(const ENGINE *e); 143 ENGINE_GEN_INT_FUNC_PTR ENGINE_get_init_function(const ENGINE *e); 144 ENGINE_GEN_INT_FUNC_PTR ENGINE_get_finish_function(const ENGINE *e); 145 ENGINE_CTRL_FUNC_PTR ENGINE_get_ctrl_function(const ENGINE *e); 146 ENGINE_LOAD_KEY_PTR ENGINE_get_load_privkey_function(const ENGINE *e); 147 ENGINE_LOAD_KEY_PTR ENGINE_get_load_pubkey_function(const ENGINE *e); 148 ENGINE_CIPHERS_PTR ENGINE_get_ciphers(const ENGINE *e); 149 ENGINE_DIGESTS_PTR ENGINE_get_digests(const ENGINE *e); 150 const EVP_CIPHER *ENGINE_get_cipher(ENGINE *e, int nid); 151 const EVP_MD *ENGINE_get_digest(ENGINE *e, int nid); 152 int ENGINE_get_flags(const ENGINE *e); 153 const ENGINE_CMD_DEFN *ENGINE_get_cmd_defns(const ENGINE *e); 154 155 EVP_PKEY *ENGINE_load_private_key(ENGINE *e, const char *key_id, 156 UI_METHOD *ui_method, void *callback_data); 157 EVP_PKEY *ENGINE_load_public_key(ENGINE *e, const char *key_id, 158 UI_METHOD *ui_method, void *callback_data); 159 160 void ENGINE_add_conf_module(void); 161 162=head1 DESCRIPTION 163 164These functions create, manipulate, and use cryptographic modules in the 165form of B<ENGINE> objects. These objects act as containers for 166implementations of cryptographic algorithms, and support a 167reference-counted mechanism to allow them to be dynamically loaded in and 168out of the running application. 169 170The cryptographic functionality that can be provided by an B<ENGINE> 171implementation includes the following abstractions; 172 173 RSA_METHOD - for providing alternative RSA implementations 174 DSA_METHOD, DH_METHOD, RAND_METHOD, ECDH_METHOD, ECDSA_METHOD, 175 STORE_METHOD - similarly for other OpenSSL APIs 176 EVP_CIPHER - potentially multiple cipher algorithms (indexed by 'nid') 177 EVP_DIGEST - potentially multiple hash algorithms (indexed by 'nid') 178 key-loading - loading public and/or private EVP_PKEY keys 179 180=head2 Reference counting and handles 181 182Due to the modular nature of the ENGINE API, pointers to ENGINEs need to be 183treated as handles - ie. not only as pointers, but also as references to 184the underlying ENGINE object. Ie. one should obtain a new reference when 185making copies of an ENGINE pointer if the copies will be used (and 186released) independently. 187 188ENGINE objects have two levels of reference-counting to match the way in 189which the objects are used. At the most basic level, each ENGINE pointer is 190inherently a B<structural> reference - a structural reference is required 191to use the pointer value at all, as this kind of reference is a guarantee 192that the structure can not be deallocated until the reference is released. 193 194However, a structural reference provides no guarantee that the ENGINE is 195initiliased and able to use any of its cryptographic 196implementations. Indeed it's quite possible that most ENGINEs will not 197initialise at all in typical environments, as ENGINEs are typically used to 198support specialised hardware. To use an ENGINE's functionality, you need a 199B<functional> reference. This kind of reference can be considered a 200specialised form of structural reference, because each functional reference 201implicitly contains a structural reference as well - however to avoid 202difficult-to-find programming bugs, it is recommended to treat the two 203kinds of reference independently. If you have a functional reference to an 204ENGINE, you have a guarantee that the ENGINE has been initialised ready to 205perform cryptographic operations and will remain uninitialised 206until after you have released your reference. 207 208I<Structural references> 209 210This basic type of reference is used for instantiating new ENGINEs, 211iterating across OpenSSL's internal linked-list of loaded 212ENGINEs, reading information about an ENGINE, etc. Essentially a structural 213reference is sufficient if you only need to query or manipulate the data of 214an ENGINE implementation rather than use its functionality. 215 216The ENGINE_new() function returns a structural reference to a new (empty) 217ENGINE object. There are other ENGINE API functions that return structural 218references such as; ENGINE_by_id(), ENGINE_get_first(), ENGINE_get_last(), 219ENGINE_get_next(), ENGINE_get_prev(). All structural references should be 220released by a corresponding to call to the ENGINE_free() function - the 221ENGINE object itself will only actually be cleaned up and deallocated when 222the last structural reference is released. 223 224It should also be noted that many ENGINE API function calls that accept a 225structural reference will internally obtain another reference - typically 226this happens whenever the supplied ENGINE will be needed by OpenSSL after 227the function has returned. Eg. the function to add a new ENGINE to 228OpenSSL's internal list is ENGINE_add() - if this function returns success, 229then OpenSSL will have stored a new structural reference internally so the 230caller is still responsible for freeing their own reference with 231ENGINE_free() when they are finished with it. In a similar way, some 232functions will automatically release the structural reference passed to it 233if part of the function's job is to do so. Eg. the ENGINE_get_next() and 234ENGINE_get_prev() functions are used for iterating across the internal 235ENGINE list - they will return a new structural reference to the next (or 236previous) ENGINE in the list or NULL if at the end (or beginning) of the 237list, but in either case the structural reference passed to the function is 238released on behalf of the caller. 239 240To clarify a particular function's handling of references, one should 241always consult that function's documentation "man" page, or failing that 242the openssl/engine.h header file includes some hints. 243 244I<Functional references> 245 246As mentioned, functional references exist when the cryptographic 247functionality of an ENGINE is required to be available. A functional 248reference can be obtained in one of two ways; from an existing structural 249reference to the required ENGINE, or by asking OpenSSL for the default 250operational ENGINE for a given cryptographic purpose. 251 252To obtain a functional reference from an existing structural reference, 253call the ENGINE_init() function. This returns zero if the ENGINE was not 254already operational and couldn't be successfully initialised (eg. lack of 255system drivers, no special hardware attached, etc), otherwise it will 256return non-zero to indicate that the ENGINE is now operational and will 257have allocated a new B<functional> reference to the ENGINE. All functional 258references are released by calling ENGINE_finish() (which removes the 259implicit structural reference as well). 260 261The second way to get a functional reference is by asking OpenSSL for a 262default implementation for a given task, eg. by ENGINE_get_default_RSA(), 263ENGINE_get_default_cipher_engine(), etc. These are discussed in the next 264section, though they are not usually required by application programmers as 265they are used automatically when creating and using the relevant 266algorithm-specific types in OpenSSL, such as RSA, DSA, EVP_CIPHER_CTX, etc. 267 268=head2 Default implementations 269 270For each supported abstraction, the ENGINE code maintains an internal table 271of state to control which implementations are available for a given 272abstraction and which should be used by default. These implementations are 273registered in the tables and indexed by an 'nid' value, because 274abstractions like EVP_CIPHER and EVP_DIGEST support many distinct 275algorithms and modes, and ENGINEs can support arbitrarily many of them. 276In the case of other abstractions like RSA, DSA, etc, there is only one 277"algorithm" so all implementations implicitly register using the same 'nid' 278index. 279 280When a default ENGINE is requested for a given abstraction/algorithm/mode, (eg. 281when calling RSA_new_method(NULL)), a "get_default" call will be made to the 282ENGINE subsystem to process the corresponding state table and return a 283functional reference to an initialised ENGINE whose implementation should be 284used. If no ENGINE should (or can) be used, it will return NULL and the caller 285will operate with a NULL ENGINE handle - this usually equates to using the 286conventional software implementation. In the latter case, OpenSSL will from 287then on behave the way it used to before the ENGINE API existed. 288 289Each state table has a flag to note whether it has processed this 290"get_default" query since the table was last modified, because to process 291this question it must iterate across all the registered ENGINEs in the 292table trying to initialise each of them in turn, in case one of them is 293operational. If it returns a functional reference to an ENGINE, it will 294also cache another reference to speed up processing future queries (without 295needing to iterate across the table). Likewise, it will cache a NULL 296response if no ENGINE was available so that future queries won't repeat the 297same iteration unless the state table changes. This behaviour can also be 298changed; if the ENGINE_TABLE_FLAG_NOINIT flag is set (using 299ENGINE_set_table_flags()), no attempted initialisations will take place, 300instead the only way for the state table to return a non-NULL ENGINE to the 301"get_default" query will be if one is expressly set in the table. Eg. 302ENGINE_set_default_RSA() does the same job as ENGINE_register_RSA() except 303that it also sets the state table's cached response for the "get_default" 304query. In the case of abstractions like EVP_CIPHER, where implementations are 305indexed by 'nid', these flags and cached-responses are distinct for each 'nid' 306value. 307 308=head2 Application requirements 309 310This section will explain the basic things an application programmer should 311support to make the most useful elements of the ENGINE functionality 312available to the user. The first thing to consider is whether the 313programmer wishes to make alternative ENGINE modules available to the 314application and user. OpenSSL maintains an internal linked list of 315"visible" ENGINEs from which it has to operate - at start-up, this list is 316empty and in fact if an application does not call any ENGINE API calls and 317it uses static linking against openssl, then the resulting application 318binary will not contain any alternative ENGINE code at all. So the first 319consideration is whether any/all available ENGINE implementations should be 320made visible to OpenSSL - this is controlled by calling the various "load" 321functions, eg. 322 323 /* Make the "dynamic" ENGINE available */ 324 void ENGINE_load_dynamic(void); 325 /* Make the CryptoSwift hardware acceleration support available */ 326 void ENGINE_load_cswift(void); 327 /* Make support for nCipher's "CHIL" hardware available */ 328 void ENGINE_load_chil(void); 329 ... 330 /* Make ALL ENGINE implementations bundled with OpenSSL available */ 331 void ENGINE_load_builtin_engines(void); 332 333Having called any of these functions, ENGINE objects would have been 334dynamically allocated and populated with these implementations and linked 335into OpenSSL's internal linked list. At this point it is important to 336mention an important API function; 337 338 void ENGINE_cleanup(void); 339 340If no ENGINE API functions are called at all in an application, then there 341are no inherent memory leaks to worry about from the ENGINE functionality, 342however if any ENGINEs are loaded, even if they are never registered or 343used, it is necessary to use the ENGINE_cleanup() function to 344correspondingly cleanup before program exit, if the caller wishes to avoid 345memory leaks. This mechanism uses an internal callback registration table 346so that any ENGINE API functionality that knows it requires cleanup can 347register its cleanup details to be called during ENGINE_cleanup(). This 348approach allows ENGINE_cleanup() to clean up after any ENGINE functionality 349at all that your program uses, yet doesn't automatically create linker 350dependencies to all possible ENGINE functionality - only the cleanup 351callbacks required by the functionality you do use will be required by the 352linker. 353 354The fact that ENGINEs are made visible to OpenSSL (and thus are linked into 355the program and loaded into memory at run-time) does not mean they are 356"registered" or called into use by OpenSSL automatically - that behaviour 357is something for the application to control. Some applications 358will want to allow the user to specify exactly which ENGINE they want used 359if any is to be used at all. Others may prefer to load all support and have 360OpenSSL automatically use at run-time any ENGINE that is able to 361successfully initialise - ie. to assume that this corresponds to 362acceleration hardware attached to the machine or some such thing. There are 363probably numerous other ways in which applications may prefer to handle 364things, so we will simply illustrate the consequences as they apply to a 365couple of simple cases and leave developers to consider these and the 366source code to openssl's builtin utilities as guides. 367 368I<Using a specific ENGINE implementation> 369 370Here we'll assume an application has been configured by its user or admin 371to want to use the "ACME" ENGINE if it is available in the version of 372OpenSSL the application was compiled with. If it is available, it should be 373used by default for all RSA, DSA, and symmetric cipher operation, otherwise 374OpenSSL should use its builtin software as per usual. The following code 375illustrates how to approach this; 376 377 ENGINE *e; 378 const char *engine_id = "ACME"; 379 ENGINE_load_builtin_engines(); 380 e = ENGINE_by_id(engine_id); 381 if(!e) 382 /* the engine isn't available */ 383 return; 384 if(!ENGINE_init(e)) { 385 /* the engine couldn't initialise, release 'e' */ 386 ENGINE_free(e); 387 return; 388 } 389 if(!ENGINE_set_default_RSA(e)) 390 /* This should only happen when 'e' can't initialise, but the previous 391 * statement suggests it did. */ 392 abort(); 393 ENGINE_set_default_DSA(e); 394 ENGINE_set_default_ciphers(e); 395 /* Release the functional reference from ENGINE_init() */ 396 ENGINE_finish(e); 397 /* Release the structural reference from ENGINE_by_id() */ 398 ENGINE_free(e); 399 400I<Automatically using builtin ENGINE implementations> 401 402Here we'll assume we want to load and register all ENGINE implementations 403bundled with OpenSSL, such that for any cryptographic algorithm required by 404OpenSSL - if there is an ENGINE that implements it and can be initialise, 405it should be used. The following code illustrates how this can work; 406 407 /* Load all bundled ENGINEs into memory and make them visible */ 408 ENGINE_load_builtin_engines(); 409 /* Register all of them for every algorithm they collectively implement */ 410 ENGINE_register_all_complete(); 411 412That's all that's required. Eg. the next time OpenSSL tries to set up an 413RSA key, any bundled ENGINEs that implement RSA_METHOD will be passed to 414ENGINE_init() and if any of those succeed, that ENGINE will be set as the 415default for RSA use from then on. 416 417=head2 Advanced configuration support 418 419There is a mechanism supported by the ENGINE framework that allows each 420ENGINE implementation to define an arbitrary set of configuration 421"commands" and expose them to OpenSSL and any applications based on 422OpenSSL. This mechanism is entirely based on the use of name-value pairs 423and assumes ASCII input (no unicode or UTF for now!), so it is ideal if 424applications want to provide a transparent way for users to provide 425arbitrary configuration "directives" directly to such ENGINEs. It is also 426possible for the application to dynamically interrogate the loaded ENGINE 427implementations for the names, descriptions, and input flags of their 428available "control commands", providing a more flexible configuration 429scheme. However, if the user is expected to know which ENGINE device he/she 430is using (in the case of specialised hardware, this goes without saying) 431then applications may not need to concern themselves with discovering the 432supported control commands and simply prefer to pass settings into ENGINEs 433exactly as they are provided by the user. 434 435Before illustrating how control commands work, it is worth mentioning what 436they are typically used for. Broadly speaking there are two uses for 437control commands; the first is to provide the necessary details to the 438implementation (which may know nothing at all specific to the host system) 439so that it can be initialised for use. This could include the path to any 440driver or config files it needs to load, required network addresses, 441smart-card identifiers, passwords to initialise protected devices, 442logging information, etc etc. This class of commands typically needs to be 443passed to an ENGINE B<before> attempting to initialise it, ie. before 444calling ENGINE_init(). The other class of commands consist of settings or 445operations that tweak certain behaviour or cause certain operations to take 446place, and these commands may work either before or after ENGINE_init(), or 447in some cases both. ENGINE implementations should provide indications of 448this in the descriptions attached to builtin control commands and/or in 449external product documentation. 450 451I<Issuing control commands to an ENGINE> 452 453Let's illustrate by example; a function for which the caller supplies the 454name of the ENGINE it wishes to use, a table of string-pairs for use before 455initialisation, and another table for use after initialisation. Note that 456the string-pairs used for control commands consist of a command "name" 457followed by the command "parameter" - the parameter could be NULL in some 458cases but the name can not. This function should initialise the ENGINE 459(issuing the "pre" commands beforehand and the "post" commands afterwards) 460and set it as the default for everything except RAND and then return a 461boolean success or failure. 462 463 int generic_load_engine_fn(const char *engine_id, 464 const char **pre_cmds, int pre_num, 465 const char **post_cmds, int post_num) 466 { 467 ENGINE *e = ENGINE_by_id(engine_id); 468 if(!e) return 0; 469 while(pre_num--) { 470 if(!ENGINE_ctrl_cmd_string(e, pre_cmds[0], pre_cmds[1], 0)) { 471 fprintf(stderr, "Failed command (%s - %s:%s)\n", engine_id, 472 pre_cmds[0], pre_cmds[1] ? pre_cmds[1] : "(NULL)"); 473 ENGINE_free(e); 474 return 0; 475 } 476 pre_cmds += 2; 477 } 478 if(!ENGINE_init(e)) { 479 fprintf(stderr, "Failed initialisation\n"); 480 ENGINE_free(e); 481 return 0; 482 } 483 /* ENGINE_init() returned a functional reference, so free the structural 484 * reference from ENGINE_by_id(). */ 485 ENGINE_free(e); 486 while(post_num--) { 487 if(!ENGINE_ctrl_cmd_string(e, post_cmds[0], post_cmds[1], 0)) { 488 fprintf(stderr, "Failed command (%s - %s:%s)\n", engine_id, 489 post_cmds[0], post_cmds[1] ? post_cmds[1] : "(NULL)"); 490 ENGINE_finish(e); 491 return 0; 492 } 493 post_cmds += 2; 494 } 495 ENGINE_set_default(e, ENGINE_METHOD_ALL & ~ENGINE_METHOD_RAND); 496 /* Success */ 497 return 1; 498 } 499 500Note that ENGINE_ctrl_cmd_string() accepts a boolean argument that can 501relax the semantics of the function - if set non-zero it will only return 502failure if the ENGINE supported the given command name but failed while 503executing it, if the ENGINE doesn't support the command name it will simply 504return success without doing anything. In this case we assume the user is 505only supplying commands specific to the given ENGINE so we set this to 506FALSE. 507 508I<Discovering supported control commands> 509 510It is possible to discover at run-time the names, numerical-ids, descriptions 511and input parameters of the control commands supported by an ENGINE using a 512structural reference. Note that some control commands are defined by OpenSSL 513itself and it will intercept and handle these control commands on behalf of the 514ENGINE, ie. the ENGINE's ctrl() handler is not used for the control command. 515openssl/engine.h defines an index, ENGINE_CMD_BASE, that all control commands 516implemented by ENGINEs should be numbered from. Any command value lower than 517this symbol is considered a "generic" command is handled directly by the 518OpenSSL core routines. 519 520It is using these "core" control commands that one can discover the the control 521commands implemented by a given ENGINE, specifically the commands; 522 523 #define ENGINE_HAS_CTRL_FUNCTION 10 524 #define ENGINE_CTRL_GET_FIRST_CMD_TYPE 11 525 #define ENGINE_CTRL_GET_NEXT_CMD_TYPE 12 526 #define ENGINE_CTRL_GET_CMD_FROM_NAME 13 527 #define ENGINE_CTRL_GET_NAME_LEN_FROM_CMD 14 528 #define ENGINE_CTRL_GET_NAME_FROM_CMD 15 529 #define ENGINE_CTRL_GET_DESC_LEN_FROM_CMD 16 530 #define ENGINE_CTRL_GET_DESC_FROM_CMD 17 531 #define ENGINE_CTRL_GET_CMD_FLAGS 18 532 533Whilst these commands are automatically processed by the OpenSSL framework code, 534they use various properties exposed by each ENGINE to process these 535queries. An ENGINE has 3 properties it exposes that can affect how this behaves; 536it can supply a ctrl() handler, it can specify ENGINE_FLAGS_MANUAL_CMD_CTRL in 537the ENGINE's flags, and it can expose an array of control command descriptions. 538If an ENGINE specifies the ENGINE_FLAGS_MANUAL_CMD_CTRL flag, then it will 539simply pass all these "core" control commands directly to the ENGINE's ctrl() 540handler (and thus, it must have supplied one), so it is up to the ENGINE to 541reply to these "discovery" commands itself. If that flag is not set, then the 542OpenSSL framework code will work with the following rules; 543 544 if no ctrl() handler supplied; 545 ENGINE_HAS_CTRL_FUNCTION returns FALSE (zero), 546 all other commands fail. 547 if a ctrl() handler was supplied but no array of control commands; 548 ENGINE_HAS_CTRL_FUNCTION returns TRUE, 549 all other commands fail. 550 if a ctrl() handler and array of control commands was supplied; 551 ENGINE_HAS_CTRL_FUNCTION returns TRUE, 552 all other commands proceed processing ... 553 554If the ENGINE's array of control commands is empty then all other commands will 555fail, otherwise; ENGINE_CTRL_GET_FIRST_CMD_TYPE returns the identifier of 556the first command supported by the ENGINE, ENGINE_GET_NEXT_CMD_TYPE takes the 557identifier of a command supported by the ENGINE and returns the next command 558identifier or fails if there are no more, ENGINE_CMD_FROM_NAME takes a string 559name for a command and returns the corresponding identifier or fails if no such 560command name exists, and the remaining commands take a command identifier and 561return properties of the corresponding commands. All except 562ENGINE_CTRL_GET_FLAGS return the string length of a command name or description, 563or populate a supplied character buffer with a copy of the command name or 564description. ENGINE_CTRL_GET_FLAGS returns a bitwise-OR'd mask of the following 565possible values; 566 567 #define ENGINE_CMD_FLAG_NUMERIC (unsigned int)0x0001 568 #define ENGINE_CMD_FLAG_STRING (unsigned int)0x0002 569 #define ENGINE_CMD_FLAG_NO_INPUT (unsigned int)0x0004 570 #define ENGINE_CMD_FLAG_INTERNAL (unsigned int)0x0008 571 572If the ENGINE_CMD_FLAG_INTERNAL flag is set, then any other flags are purely 573informational to the caller - this flag will prevent the command being usable 574for any higher-level ENGINE functions such as ENGINE_ctrl_cmd_string(). 575"INTERNAL" commands are not intended to be exposed to text-based configuration 576by applications, administrations, users, etc. These can support arbitrary 577operations via ENGINE_ctrl(), including passing to and/or from the control 578commands data of any arbitrary type. These commands are supported in the 579discovery mechanisms simply to allow applications determinie if an ENGINE 580supports certain specific commands it might want to use (eg. application "foo" 581might query various ENGINEs to see if they implement "FOO_GET_VENDOR_LOGO_GIF" - 582and ENGINE could therefore decide whether or not to support this "foo"-specific 583extension). 584 585=head2 Future developments 586 587The ENGINE API and internal architecture is currently being reviewed. Slated for 588possible release in 0.9.8 is support for transparent loading of "dynamic" 589ENGINEs (built as self-contained shared-libraries). This would allow ENGINE 590implementations to be provided independently of OpenSSL libraries and/or 591OpenSSL-based applications, and would also remove any requirement for 592applications to explicitly use the "dynamic" ENGINE to bind to shared-library 593implementations. 594 595=head1 SEE ALSO 596 597L<rsa(3)|rsa(3)>, L<dsa(3)|dsa(3)>, L<dh(3)|dh(3)>, L<rand(3)|rand(3)> 598 599=cut 600