engine(3)                   OpenSSL                   engine(3)





NAME
       engine - ENGINE cryptographic module support

SYNOPSIS
        #include <openssl/engine.h>

        ENGINE *ENGINE_get_first(void);
        ENGINE *ENGINE_get_last(void);
        ENGINE *ENGINE_get_next(ENGINE *e);
        ENGINE *ENGINE_get_prev(ENGINE *e);

        int ENGINE_add(ENGINE *e);
        int ENGINE_remove(ENGINE *e);

        ENGINE *ENGINE_by_id(const char *id);

        int ENGINE_init(ENGINE *e);
        int ENGINE_finish(ENGINE *e);

        void ENGINE_load_openssl(void);
        void ENGINE_load_dynamic(void);
        void ENGINE_load_cswift(void);
        void ENGINE_load_chil(void);
        void ENGINE_load_atalla(void);
        void ENGINE_load_nuron(void);
        void ENGINE_load_ubsec(void);
        void ENGINE_load_aep(void);
        void ENGINE_load_sureware(void);
        void ENGINE_load_4758cca(void);
        void ENGINE_load_openbsd_dev_crypto(void);
        void ENGINE_load_builtin_engines(void);

        void ENGINE_cleanup(void);

        ENGINE *ENGINE_get_default_RSA(void);
        ENGINE *ENGINE_get_default_DSA(void);
        ENGINE *ENGINE_get_default_DH(void);
        ENGINE *ENGINE_get_default_RAND(void);
        ENGINE *ENGINE_get_cipher_engine(int nid);
        ENGINE *ENGINE_get_digest_engine(int nid);

        int ENGINE_set_default_RSA(ENGINE *e);
        int ENGINE_set_default_DSA(ENGINE *e);
        int ENGINE_set_default_DH(ENGINE *e);
        int ENGINE_set_default_RAND(ENGINE *e);
        int ENGINE_set_default_ciphers(ENGINE *e);
        int ENGINE_set_default_digests(ENGINE *e);
        int ENGINE_set_default_string(ENGINE *e, const char *list);

        int ENGINE_set_default(ENGINE *e, unsigned int flags);

        unsigned int ENGINE_get_table_flags(void);
        void ENGINE_set_table_flags(unsigned int flags);











        int ENGINE_register_RSA(ENGINE *e);
        void ENGINE_unregister_RSA(ENGINE *e);
        void ENGINE_register_all_RSA(void);
        int ENGINE_register_DSA(ENGINE *e);
        void ENGINE_unregister_DSA(ENGINE *e);
        void ENGINE_register_all_DSA(void);
        int ENGINE_register_DH(ENGINE *e);
        void ENGINE_unregister_DH(ENGINE *e);
        void ENGINE_register_all_DH(void);
        int ENGINE_register_RAND(ENGINE *e);
        void ENGINE_unregister_RAND(ENGINE *e);
        void ENGINE_register_all_RAND(void);
        int ENGINE_register_ciphers(ENGINE *e);
        void ENGINE_unregister_ciphers(ENGINE *e);
        void ENGINE_register_all_ciphers(void);
        int ENGINE_register_digests(ENGINE *e);
        void ENGINE_unregister_digests(ENGINE *e);
        void ENGINE_register_all_digests(void);
        int ENGINE_register_complete(ENGINE *e);
        int ENGINE_register_all_complete(void);

        int ENGINE_ctrl(ENGINE *e, int cmd, long i, void *p, void (*f)());
        int ENGINE_cmd_is_executable(ENGINE *e, int cmd);
        int ENGINE_ctrl_cmd(ENGINE *e, const char *cmd_name,
                long i, void *p, void (*f)(), int cmd_optional);
        int ENGINE_ctrl_cmd_string(ENGINE *e, const char *cmd_name, const char *arg,
                        int cmd_optional);

        int ENGINE_set_ex_data(ENGINE *e, int idx, void *arg);
        void *ENGINE_get_ex_data(const ENGINE *e, int idx);

        int ENGINE_get_ex_new_index(long argl, void *argp, CRYPTO_EX_new *new_func,
                CRYPTO_EX_dup *dup_func, CRYPTO_EX_free *free_func);

        ENGINE *ENGINE_new(void);
        int ENGINE_free(ENGINE *e);

        int ENGINE_set_id(ENGINE *e, const char *id);
        int ENGINE_set_name(ENGINE *e, const char *name);
        int ENGINE_set_RSA(ENGINE *e, const RSA_METHOD *rsa_meth);
        int ENGINE_set_DSA(ENGINE *e, const DSA_METHOD *dsa_meth);
        int ENGINE_set_DH(ENGINE *e, const DH_METHOD *dh_meth);
        int ENGINE_set_RAND(ENGINE *e, const RAND_METHOD *rand_meth);
        int ENGINE_set_destroy_function(ENGINE *e, ENGINE_GEN_INT_FUNC_PTR destroy_f);
        int ENGINE_set_init_function(ENGINE *e, ENGINE_GEN_INT_FUNC_PTR init_f);
        int ENGINE_set_finish_function(ENGINE *e, ENGINE_GEN_INT_FUNC_PTR finish_f);
        int ENGINE_set_ctrl_function(ENGINE *e, ENGINE_CTRL_FUNC_PTR ctrl_f);
        int ENGINE_set_load_privkey_function(ENGINE *e, ENGINE_LOAD_KEY_PTR loadpriv_f);
        int ENGINE_set_load_pubkey_function(ENGINE *e, ENGINE_LOAD_KEY_PTR loadpub_f);
        int ENGINE_set_ciphers(ENGINE *e, ENGINE_CIPHERS_PTR f);
        int ENGINE_set_digests(ENGINE *e, ENGINE_DIGESTS_PTR f);
        int ENGINE_set_flags(ENGINE *e, int flags);
        int ENGINE_set_cmd_defns(ENGINE *e, const ENGINE_CMD_DEFN *defns);

















        const char *ENGINE_get_id(const ENGINE *e);
        const char *ENGINE_get_name(const ENGINE *e);
        const RSA_METHOD *ENGINE_get_RSA(const ENGINE *e);
        const DSA_METHOD *ENGINE_get_DSA(const ENGINE *e);
        const DH_METHOD *ENGINE_get_DH(const ENGINE *e);
        const RAND_METHOD *ENGINE_get_RAND(const ENGINE *e);
        ENGINE_GEN_INT_FUNC_PTR ENGINE_get_destroy_function(const ENGINE *e);
        ENGINE_GEN_INT_FUNC_PTR ENGINE_get_init_function(const ENGINE *e);
        ENGINE_GEN_INT_FUNC_PTR ENGINE_get_finish_function(const ENGINE *e);
        ENGINE_CTRL_FUNC_PTR ENGINE_get_ctrl_function(const ENGINE *e);
        ENGINE_LOAD_KEY_PTR ENGINE_get_load_privkey_function(const ENGINE *e);
        ENGINE_LOAD_KEY_PTR ENGINE_get_load_pubkey_function(const ENGINE *e);
        ENGINE_CIPHERS_PTR ENGINE_get_ciphers(const ENGINE *e);
        ENGINE_DIGESTS_PTR ENGINE_get_digests(const ENGINE *e);
        const EVP_CIPHER *ENGINE_get_cipher(ENGINE *e, int nid);
        const EVP_MD *ENGINE_get_digest(ENGINE *e, int nid);
        int ENGINE_get_flags(const ENGINE *e);
        const ENGINE_CMD_DEFN *ENGINE_get_cmd_defns(const ENGINE *e);

        EVP_PKEY *ENGINE_load_private_key(ENGINE *e, const char *key_id,
            UI_METHOD *ui_method, void *callback_data);
        EVP_PKEY *ENGINE_load_public_key(ENGINE *e, const char *key_id,
            UI_METHOD *ui_method, void *callback_data);

        void ENGINE_add_conf_module(void);

DESCRIPTION
       These functions create, manipulate, and use crypto-
       graphic modules in the form of ENGINE objects. These
       objects act as containers for implementations of crypto-
       graphic algorithms, and support a reference-counted
       mechanism to allow them to be dynamically loaded in and
       out of the running application.

       The cryptographic functionality that can be provided by
       an ENGINE implementation includes the following abstrac-
       tions;

        RSA_METHOD - for providing alternative RSA implementations
        DSA_METHOD, DH_METHOD, RAND_METHOD - alternative DSA, DH, and RAND
        EVP_CIPHER - potentially multiple cipher algorithms (indexed by 'nid')
        EVP_DIGEST - potentially multiple hash algorithms (indexed by 'nid')
        key-loading - loading public and/or private EVP_PKEY keys

       Reference counting and handles

       Due to the modular nature of the ENGINE API, pointers to
       ENGINEs need to be treated as handles - ie. not only as
       pointers, but also as references to the underlying
       ENGINE object. Ie. you should obtain a new reference
       when making copies of an ENGINE pointer if the copies
       will be used (and released) independantly.

       ENGINE objects have two levels of reference-counting to
       match the way in which the objects are used. At the most
       basic level, each ENGINE pointer is inherently a struc-
       tural reference - you need a structural reference simply
       to refer to the pointer value at all, as this kind of
       reference is your guarantee that the structure can not
       be deallocated until you release your reference.

       However, a structural reference provides no guarantee
       that the ENGINE has been initiliased to be usable to
       perform any of its cryptographic implementations - and
       indeed it's quite possible that most ENGINEs will not
       initialised at all on standard setups, as ENGINEs are
       typically used to support specialised hardware. To use
       an ENGINE's functionality, you need a functional refer-
       ence. This kind of reference can be considered a spe-
       cialised form of structural reference, because each
       functional reference implicitly contains a structural
       reference as well - however to avoid difficult-to-find
       programming bugs, it is recommended to treat the two
       kinds of reference independantly. If you have a func-
       tional reference to an ENGINE, you have a guarantee that
       the ENGINE has been initialised ready to perform crypto-
       graphic operations and will not be uninitialised or
       cleaned up until after you have released your reference.

       We will discuss the two kinds of reference separately,
       including how to tell which one you are dealing with at
       any given point in time (after all they are both simply
       (ENGINE *) pointers, the difference is in the way they
       are used).

       Structural references

       This basic type of reference is typically used for cre-
       ating new ENGINEs dynamically, iterating across
       OpenSSL's internal linked-list of loaded ENGINEs, read-
       ing information about an ENGINE, etc. Essentially a
       structural reference is sufficient if you only need to
       query or manipulate the data of an ENGINE implementation
       rather than use its functionality.

       The ENGINE_new() function returns a structural reference
       to a new (empty) ENGINE object. Other than that, struc-
       tural references come from return values to various
       ENGINE API functions such as; ENGINE_by_id(),
       ENGINE_get_first(), ENGINE_get_last(),
       ENGINE_get_next(), ENGINE_get_prev(). All structural
       references should be released by a corresponding to call
       to the ENGINE_free() function - the ENGINE object itself
       will only actually be cleaned up and deallocated when
       the last structural reference is released.

       It should also be noted that many ENGINE API function
       calls that accept a structural reference will internally
       obtain another reference - typically this happens when-
       ever the supplied ENGINE will be needed by OpenSSL after
       the function has returned. Eg. the function to add a new
       ENGINE to OpenSSL's internal list is ENGINE_add() - if
       this function returns success, then OpenSSL will have
       stored a new structural reference internally so the
       caller is still responsible for freeing their own refer-
       ence with ENGINE_free() when they are finished with it.
       In a similar way, some functions will automatically
       release the structural reference passed to it if part of
       the function's job is to do so. Eg. the
       ENGINE_get_next() and ENGINE_get_prev() functions are
       used for iterating across the internal ENGINE list -
       they will return a new structural reference to the next
       (or previous) ENGINE in the list or NULL if at the end
       (or beginning) of the list, but in either case the
       structural reference passed to the function is released
       on behalf of the caller.

       To clarify a particular function's handling of refer-
       ences, one should always consult that function's docu-
       mentation "man" page, or failing that the
       openssl/engine.h header file includes some hints.

       Functional references

       As mentioned, functional references exist when the cryp-
       tographic functionality of an ENGINE is required to be
       available. A functional reference can be obtained in one
       of two ways; from an existing structural reference to
       the required ENGINE, or by asking OpenSSL for the
       default operational ENGINE for a given cryptographic
       purpose.

       To obtain a functional reference from an existing struc-
       tural reference, call the ENGINE_init() function. This
       returns zero if the ENGINE was not already operational
       and couldn't be successfully initialised (eg. lack of
       system drivers, no special hardware attached, etc), oth-
       erwise it will return non-zero to indicate that the
       ENGINE is now operational and will have allocated a new
       functional reference to the ENGINE. In this case, the
       supplied ENGINE pointer is, from the point of the view
       of the caller, both a structural reference and a func-
       tional reference - so if the caller intends to use it as
       a functional reference it should free the structural
       reference with ENGINE_free() first. If the caller wishes
       to use it only as a structural reference (eg. if the
       ENGINE_init() call was simply to test if the ENGINE
       seems available/online), then it should free the func-
       tional reference; all functional references are released
       by the ENGINE_finish() function.

       The second way to get a functional reference is by ask-
       ing OpenSSL for a default implementation for a given
       task, eg. by ENGINE_get_default_RSA(),
       ENGINE_get_default_cipher_engine(), etc. These are dis-
       cussed in the next section, though they are not usually
       required by application programmers as they are used
       automatically when creating and using the relevant algo-
       rithm-specific types in OpenSSL, such as RSA, DSA,
       EVP_CIPHER_CTX, etc.

       Default implementations

       For each supported abstraction, the ENGINE code main-
       tains an internal table of state to control which imple-
       mentations are available for a given abstraction and
       which should be used by default. These implementations
       are registered in the tables separated-out by an 'nid'
       index, because abstractions like EVP_CIPHER and
       EVP_DIGEST support many distinct algorithms and modes -
       ENGINEs will support different numbers and combinations
       of these. In the case of other abstractions like RSA,
       DSA, etc, there is only one "algorithm" so all implemen-
       tations implicitly register using the same 'nid' index.
       ENGINEs can be registered into these tables to make
       themselves available for use automatically by the vari-
       ous abstractions, eg. RSA. For illustrative purposes, we
       continue with the RSA example, though all comments apply
       similarly to the other abstractions (they each get their
       own table and linkage to the corresponding section of
       openssl code).

       When a new RSA key is being created, ie. in
       RSA_new_method(), a "get_default" call will be made to
       the ENGINE subsystem to process the RSA state table and
       return a functional reference to an initialised ENGINE
       whose RSA_METHOD should be used. If no ENGINE should (or
       can) be used, it will return NULL and the RSA key will
       operate with a NULL ENGINE handle by using the conven-
       tional RSA implementation in OpenSSL (and will from then
       on behave the way it used to before the ENGINE API
       existed - for details see RSA_new_method(3)).

       Each state table has a flag to note whether it has pro-
       cessed this "get_default" query since the table was last
       modified, because to process this question it must iter-
       ate across all the registered ENGINEs in the table try-
       ing to initialise each of them in turn, in case one of
       them is operational. If it returns a functional refer-
       ence to an ENGINE, it will also cache another reference
       to speed up processing future queries (without needing
       to iterate across the table). Likewise, it will cache a
       NULL response if no ENGINE was available so that future
       queries won't repeat the same iteration unless the state
       table changes. This behaviour can also be changed; if
       the ENGINE_TABLE_FLAG_NOINIT flag is set (using
       ENGINE_set_table_flags()), no attempted initialisations
       will take place, instead the only way for the state ta-
       ble to return a non-NULL ENGINE to the "get_default"
       query will be if one is expressly set in the table. Eg.
       ENGINE_set_default_RSA() does the same job as
       ENGINE_register_RSA() except that it also sets the state
       table's cached response for the "get_default" query.

       In the case of abstractions like EVP_CIPHER, where
       implementations are indexed by 'nid', these flags and
       cached-responses are distinct for each 'nid' value.

       It is worth illustrating the difference between "regis-
       tration" of ENGINEs into these per-algorithm state
       tables and using the alternative "set_default" func-
       tions. The latter handles both "registration" and also
       setting the cached "default" ENGINE in each relevant
       state table - so registered ENGINEs will only have a
       chance to be initialised for use as a default if a
       default ENGINE wasn't already set for the same state ta-
       ble.  Eg. if ENGINE X supports cipher nids {A,B} and
       RSA, ENGINE Y supports ciphers {A} and DSA, and the fol-
       lowing code is executed;

        ENGINE_register_complete(X);
        ENGINE_set_default(Y, ENGINE_METHOD_ALL);
        e1 = ENGINE_get_default_RSA();
        e2 = ENGINE_get_cipher_engine(A);
        e3 = ENGINE_get_cipher_engine(B);
        e4 = ENGINE_get_default_DSA();
        e5 = ENGINE_get_cipher_engine(C);

       The results would be as follows;

        assert(e1 == X);
        assert(e2 == Y);
        assert(e3 == X);
        assert(e4 == Y);
        assert(e5 == NULL);

       Application requirements

       This section will explain the basic things an applica-
       tion programmer should support to make the most useful
       elements of the ENGINE functionality available to the
       user. The first thing to consider is whether the pro-
       grammer wishes to make alternative ENGINE modules avail-
       able to the application and user. OpenSSL maintains an
       internal linked list of "visible" ENGINEs from which it
       has to operate - at start-up, this list is empty and in
       fact if an application does not call any ENGINE API
       calls and it uses static linking against openssl, then
       the resulting application binary will not contain any
       alternative ENGINE code at all. So the first considera-
       tion is whether any/all available ENGINE implementations
       should be made visible to OpenSSL - this is controlled
       by calling the various "load" functions, eg.







        /* Make the "dynamic" ENGINE available */
        void ENGINE_load_dynamic(void);
        /* Make the CryptoSwift hardware acceleration support available */
        void ENGINE_load_cswift(void);
        /* Make support for nCipher's "CHIL" hardware available */
        void ENGINE_load_chil(void);
        ...
        /* Make ALL ENGINE implementations bundled with OpenSSL available */
        void ENGINE_load_builtin_engines(void);

       Having called any of these functions, ENGINE objects
       would have been dynamically allocated and populated with
       these implementations and linked into OpenSSL's internal
       linked list. At this point it is important to mention an
       important API function;

        void ENGINE_cleanup(void);

       If no ENGINE API functions are called at all in an
       application, then there are no inherent memory leaks to
       worry about from the ENGINE functionality, however if
       any ENGINEs are "load"ed, even if they are never regis-
       tered or used, it is necessary to use the
       ENGINE_cleanup() function to correspondingly cleanup
       before program exit, if the caller wishes to avoid mem-
       ory leaks. This mechanism uses an internal callback reg-
       istration table so that any ENGINE API functionality
       that knows it requires cleanup can register its cleanup
       details to be called during ENGINE_cleanup(). This
       approach allows ENGINE_cleanup() to clean up after any
       ENGINE functionality at all that your program uses, yet
       doesn't automatically create linker dependencies to all
       possible ENGINE functionality - only the cleanup call-
       backs required by the functionality you do use will be
       required by the linker.

       The fact that ENGINEs are made visible to OpenSSL (and
       thus are linked into the program and loaded into memory
       at run-time) does not mean they are "registered" or
       called into use by OpenSSL automatically - that behav-
       iour is something for the application to have control
       over. Some applications will want to allow the user to
       specify exactly which ENGINE they want used if any is to
       be used at all. Others may prefer to load all support
       and have OpenSSL automatically use at run-time any
       ENGINE that is able to successfully initialise - ie. to
       assume that this corresponds to acceleration hardware
       attached to the machine or some such thing. There are
       probably numerous other ways in which applications may
       prefer to handle things, so we will simply illustrate
       the consequences as they apply to a couple of simple
       cases and leave developers to consider these and the
       source code to openssl's builtin utilities as guides.

       Using a specific ENGINE implementation

       Here we'll assume an application has been configured by
       its user or admin to want to use the "ACME" ENGINE if it
       is available in the version of OpenSSL the application
       was compiled with. If it is available, it should be used
       by default for all RSA, DSA, and symmetric cipher opera-
       tion, otherwise OpenSSL should use its builtin software
       as per usual. The following code illustrates how to
       approach this;






        ENGINE *e;
        const char *engine_id = "ACME";
        ENGINE_load_builtin_engines();
        e = ENGINE_by_id(engine_id);
        if(!e)
            /* the engine isn't available */
            return;
        if(!ENGINE_init(e)) {
            /* the engine couldn't initialise, release 'e' */
            ENGINE_free(e);
            return;
        }
        if(!ENGINE_set_default_RSA(e))
            /* This should only happen when 'e' can't initialise, but the previous
             * statement suggests it did. */
            abort();
        ENGINE_set_default_DSA(e);
        ENGINE_set_default_ciphers(e);
        /* Release the functional reference from ENGINE_init() */
        ENGINE_finish(e);
        /* Release the structural reference from ENGINE_by_id() */
        ENGINE_free(e);

       Automatically using builtin ENGINE implementations

       Here we'll assume we want to load and register all
       ENGINE implementations bundled with OpenSSL, such that
       for any cryptographic algorithm required by OpenSSL - if
       there is an ENGINE that implements it and can be ini-
       tialise, it should be used. The following code illus-
       trates how this can work;

        /* Load all bundled ENGINEs into memory and make them visible */
        ENGINE_load_builtin_engines();
        /* Register all of them for every algorithm they collectively implement */
        ENGINE_register_all_complete();

       That's all that's required. Eg. the next time OpenSSL
       tries to set up an RSA key, any bundled ENGINEs that
       implement RSA_METHOD will be passed to ENGINE_init() and
       if any of those succeed, that ENGINE will be set as the
       default for use with RSA from then on.

       Advanced configuration support

       There is a mechanism supported by the ENGINE framework
       that allows each ENGINE implementation to define an
       arbitrary set of configuration "commands" and expose
       them to OpenSSL and any applications based on OpenSSL.
       This mechanism is entirely based on the use of name-
       value pairs and and assumes ASCII input (no unicode or
       UTF for now!), so it is ideal if applications want to
       provide a transparent way for users to provide arbitrary
       configuration "directives" directly to such ENGINEs. It
       is also possible for the application to dynamically
       interrogate the loaded ENGINE implementations for the
       names, descriptions, and input flags of their available
       "control commands", providing a more flexible configura-
       tion scheme. However, if the user is expected to know
       which ENGINE device he/she is using (in the case of spe-
       cialised hardware, this goes without saying) then appli-
       cations may not need to concern themselves with discov-
       ering the supported control commands and simply prefer
       to allow settings to passed into ENGINEs exactly as they
       are provided by the user.

       Before illustrating how control commands work, it is
       worth mentioning what they are typically used for.
       Broadly speaking there are two uses for control com-
       mands; the first is to provide the necessary details to
       the implementation (which may know nothing at all spe-
       cific to the host system) so that it can be initialised
       for use. This could include the path to any driver or
       config files it needs to load, required network
       addresses, smart-card identifiers, passwords to ini-
       tialise password-protected devices, logging information,
       etc etc. This class of commands typically needs to be
       passed to an ENGINE before attempting to initialise it,
       ie. before calling ENGINE_init(). The other class of
       commands consist of settings or operations that tweak
       certain behaviour or cause certain operations to take
       place, and these commands may work either before or
       after ENGINE_init(), or in same cases both. ENGINE
       implementations should provide indications of this in
       the descriptions attached to builtin control commands
       and/or in external product documentation.

       Issuing control commands to an ENGINE

       Let's illustrate by example; a function for which the
       caller supplies the name of the ENGINE it wishes to use,
       a table of string-pairs for use before initialisation,
       and another table for use after initialisation. Note
       that the string-pairs used for control commands consist
       of a command "name" followed by the command "parameter"
       - the parameter could be NULL in some cases but the name
       can not. This function should initialise the ENGINE
       (issuing the "pre" commands beforehand and the "post"
       commands afterwards) and set it as the default for
       everything except RAND and then return a boolean success
       or failure.

        int generic_load_engine_fn(const char *engine_id,
                                   const char **pre_cmds, int pre_num,
                                   const char **post_cmds, int post_num)
        {
            ENGINE *e = ENGINE_by_id(engine_id);
            if(!e) return 0;
            while(pre_num--) {
                if(!ENGINE_ctrl_cmd_string(e, pre_cmds[0], pre_cmds[1], 0)) {
                    fprintf(stderr, "Failed command (%s - %s:%s)\n", engine_id,
                        pre_cmds[0], pre_cmds[1] ? pre_cmds[1] : "(NULL)");
                    ENGINE_free(e);
                    return 0;
                }
                pre_cmds += 2;
            }
            if(!ENGINE_init(e)) {
                fprintf(stderr, "Failed initialisation\n");
                ENGINE_free(e);
                return 0;
            }
            /* ENGINE_init() returned a functional reference, so free the structural
             * reference from ENGINE_by_id(). */
            ENGINE_free(e);
            while(post_num--) {
                if(!ENGINE_ctrl_cmd_string(e, post_cmds[0], post_cmds[1], 0)) {
                    fprintf(stderr, "Failed command (%s - %s:%s)\n", engine_id,
                        post_cmds[0], post_cmds[1] ? post_cmds[1] : "(NULL)");
                    ENGINE_finish(e);
                    return 0;
                }
                post_cmds += 2;
            }
            ENGINE_set_default(e, ENGINE_METHOD_ALL & ~ENGINE_METHOD_RAND);
            /* Success */
            return 1;
        }

       Note that ENGINE_ctrl_cmd_string() accepts a boolean
       argument that can relax the semantics of the function -
       if set non-zero it will only return failure if the
       ENGINE supported the given command name but failed while
       executing it, if the ENGINE doesn't support the command
       name it will simply return success without doing any-
       thing. In this case we assume the user is only supplying
       commands specific to the given ENGINE so we set this to
       FALSE.

       Discovering supported control commands

       It is possible to discover at run-time the names, numer-
       ical-ids, descriptions and input parameters of the con-
       trol commands supported from a structural reference to
       any ENGINE. It is first important to note that some con-
       trol commands are defined by OpenSSL itself and it will
       intercept and handle these control commands on behalf of
       the ENGINE, ie. the ENGINE's ctrl() handler is not used
       for the control command. openssl/engine.h defines a sym-
       bol, ENGINE_CMD_BASE, that all control commands imple-
       mented by ENGINEs from. Any command value lower than
       this symbol is considered a "generic" command is handled
       directly by the OpenSSL core routines.

       It is using these "core" control commands that one can
       discover the the control commands implemented by a given
       ENGINE, specifically the commands;

        #define ENGINE_HAS_CTRL_FUNCTION               10
        #define ENGINE_CTRL_GET_FIRST_CMD_TYPE         11
        #define ENGINE_CTRL_GET_NEXT_CMD_TYPE          12
        #define ENGINE_CTRL_GET_CMD_FROM_NAME          13
        #define ENGINE_CTRL_GET_NAME_LEN_FROM_CMD      14
        #define ENGINE_CTRL_GET_NAME_FROM_CMD          15
        #define ENGINE_CTRL_GET_DESC_LEN_FROM_CMD      16
        #define ENGINE_CTRL_GET_DESC_FROM_CMD          17
        #define ENGINE_CTRL_GET_CMD_FLAGS              18

       Whilst these commands are automatically processed by the
       OpenSSL framework code, they use various properties
       exposed by each ENGINE by which to process these
       queries. An ENGINE has 3 properties it exposes that can
       affect this behaviour; it can supply a ctrl() handler,
       it can specify ENGINE_FLAGS_MANUAL_CMD_CTRL in the
       ENGINE's flags, and it can expose an array of control
       command descriptions.  If an ENGINE specifies the
       ENGINE_FLAGS_MANUAL_CMD_CTRL flag, then it will simply
       pass all these "core" control commands directly to the
       ENGINE's ctrl() handler (and thus, it must have supplied
       one), so it is up to the ENGINE to reply to these "dis-
       covery" commands itself. If that flag is not set, then
       the OpenSSL framework code will work with the following
       rules;

        if no ctrl() handler supplied;
            ENGINE_HAS_CTRL_FUNCTION returns FALSE (zero),
            all other commands fail.
        if a ctrl() handler was supplied but no array of control commands;
            ENGINE_HAS_CTRL_FUNCTION returns TRUE,
            all other commands fail.
        if a ctrl() handler and array of control commands was supplied;
            ENGINE_HAS_CTRL_FUNCTION returns TRUE,
            all other commands proceed processing ...

       If the ENGINE's array of control commands is empty then
       all other commands will fail, otherwise;
       ENGINE_CTRL_GET_FIRST_CMD_TYPE returns the identifier of
       the first command supported by the ENGINE,
       ENGINE_GET_NEXT_CMD_TYPE takes the identifier of a com-
       mand supported by the ENGINE and returns the next
       command identifier or fails if there are no more,
       ENGINE_CMD_FROM_NAME takes a string name for a command
       and returns the corresponding identifier or fails if no
       such command name exists, and the remaining commands
       take a command identifier and return properties of the
       corresponding commands. All except ENGINE_CTRL_GET_FLAGS
       return the string length of a command name or descrip-
       tion, or populate a supplied character buffer with a
       copy of the command name or description.
       ENGINE_CTRL_GET_FLAGS returns a bitwise-OR'd mask of the
       following possible values;

        #define ENGINE_CMD_FLAG_NUMERIC                (unsigned int)0x0001
        #define ENGINE_CMD_FLAG_STRING                 (unsigned int)0x0002
        #define ENGINE_CMD_FLAG_NO_INPUT               (unsigned int)0x0004
        #define ENGINE_CMD_FLAG_INTERNAL               (unsigned int)0x0008

       If the ENGINE_CMD_FLAG_INTERNAL flag is set, then any
       other flags are purely informational to the caller -
       this flag will prevent the command being usable for any
       higher-level ENGINE functions such as
       ENGINE_ctrl_cmd_string().  "INTERNAL" commands are not
       intended to be exposed to text-based configuration by
       applications, administrations, users, etc. These can
       support arbitrary operations via ENGINE_ctrl(), includ-
       ing passing to and/or from the control commands data of
       any arbitrary type. These commands are supported in the
       discovery mechanisms simply to allow applications deter-
       minie if an ENGINE supports certain specific commands it
       might want to use (eg. application "foo" might query
       various ENGINEs to see if they implement "FOO_GET_VEN-
       DOR_LOGO_GIF" - and ENGINE could therefore decide
       whether or not to support this "foo"-specific exten-
       sion).

       Future developments

       The ENGINE API and internal architecture is currently
       being reviewed. Slated for possible release in 0.9.8 is
       support for transparent loading of "dynamic" ENGINEs
       (built as self-contained shared-libraries). This would
       allow ENGINE implementations to be provided indepen-
       dantly of OpenSSL libraries and/or OpenSSL-based appli-
       cations, and would also remove any requirement for
       applications to explicitly use the "dynamic" ENGINE to
       bind to shared-library implementations.

SEE ALSO
       rsa(3), dsa(3), dh(3), rand(3), RSA_new_method(3)



0.9.7c                     2002-12-15                 engine(3)
