MirOS Manual: engine(3)


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);

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ENGINE(3)                    OpenSSL                    ENGINE(3)

      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);

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ENGINE(3)                    OpenSSL                    ENGINE(3)

      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 cryptographic
     modules in the form of ENGINE objects. These objects act as
     containers for implementations of cryptographic 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 abstractions;

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ENGINE(3)                    OpenSSL                    ENGINE(3)

      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 structural
     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 reference. This kind of reference can be
     considered a specialised 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 functional
     reference to an ENGINE, you have a guarantee that the ENGINE
     has been initialised ready to perform cryptographic opera-
     tions 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 creating
     new ENGINEs dynamically, iterating across OpenSSL's internal
     linked-list of loaded ENGINEs, reading information about an
     ENGINE, etc. Essentially a structural reference is suffi-
     cient if you only need to query or manipulate the data of an

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ENGINE(3)                    OpenSSL                    ENGINE(3)

     ENGINE implementation rather than use its functionality.

     The ENGINE_new() function returns a structural reference to
     a new (empty) ENGINE object. Other than that, structural
     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 whenever the sup-
     plied 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 struc-
     tural reference internally so the caller is still responsi-
     ble for freeing their own reference 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 references,
     one should always consult that function's documentation
     "man" page, or failing that the openssl/engine.h header file
     includes some hints.

     Functional references

     As mentioned, functional references exist when the crypto-
     graphic functionality of an ENGINE is required to be avail-
     able. 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 structural
     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), otherwise it will return
     non-zero to indicate that the ENGINE is now operational and
     will have allocated a new functional reference to the

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ENGINE(3)                    OpenSSL                    ENGINE(3)

     ENGINE. In this case, the supplied ENGINE pointer is, from
     the point of the view of the caller, both a structural
     reference and a functional 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 functional
     reference; all functional references are released by the
     ENGINE_finish() function.

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

     Default implementations

     For each supported abstraction, the ENGINE code maintains an
     internal table of state to control which implementations 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 algo-
     rithms 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
     implementations implicitly register using the same 'nid'
     index. ENGINEs can be registered into these tables to make
     themselves available for use automatically by the various
     abstractions, eg. RSA. For illustrative purposes, we con-
     tinue with the RSA example, though all comments apply simi-
     larly 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 conventional RSA implemen-
     tation 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)).

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ENGINE(3)                    OpenSSL                    ENGINE(3)

     Each state table has a flag to note whether it has processed
     this "get_default" query since the table was last modified,
     because to process this question it must iterate across all
     the registered ENGINEs in the table trying to initialise
     each of them in turn, in case one of them is operational. If
     it returns a functional reference to an ENGINE, it will also
     cache another reference to speed up processing future
     queries (without needing to iterate across the table). Like-
     wise, it will cache a NULL response if no ENGINE was avail-
     able 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 table 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 implemen-
     tations are indexed by 'nid', these flags and cached-
     responses are distinct for each 'nid' value.

     It is worth illustrating the difference between "registra-
     tion" of ENGINEs into these per-algorithm state tables and
     using the alternative "set_default" functions. 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 table. Eg. if ENGINE X supports cipher
     nids {A,B} and RSA, ENGINE Y supports ciphers {A} and DSA,
     and the following 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);

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ENGINE(3)                    OpenSSL                    ENGINE(3)

     Application requirements

     This section will explain the basic things an application
     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 programmer wishes to make
     alternative ENGINE modules available 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 con-
     tain any alternative ENGINE code at all. So the first con-
     sideration is whether any/all available ENGINE implementa-
     tions 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 applica-
     tion, 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 registered or used, it is
     necessary to use the ENGINE_cleanup() function to
     correspondingly cleanup before program exit, if the caller
     wishes to avoid memory leaks. This mechanism uses an inter-
     nal callback registration table so that any ENGINE API func-
     tionality 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 pos-
     sible ENGINE functionality - only the cleanup callbacks
     required by the functionality you do use will be required by
     the linker.

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ENGINE(3)                    OpenSSL                    ENGINE(3)

     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 behaviour 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 ini-
     tialise - ie. to assume that this corresponds to accelera-
     tion 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 com-
     piled with. If it is available, it should be used by default
     for all RSA, DSA, and symmetric cipher operation, 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

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ENGINE(3)                    OpenSSL                    ENGINE(3)

     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 initialise, it should
     be used. The following code illustrates 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 appli-
     cation to dynamically interrogate the loaded ENGINE imple-
     mentations for the names, descriptions, and input flags of
     their available "control commands", providing a more flexi-
     ble configuration scheme. However, if the user is expected
     to know which ENGINE device he/she is using (in the case of
     specialised hardware, this goes without saying) then appli-
     cations may not need to concern themselves with discovering
     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 speak-
     ing there are two uses for control commands; the first is to
     provide the necessary details to the implementation (which
     may know nothing at all specific 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

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ENGINE(3)                    OpenSSL                    ENGINE(3)

     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 indica-
     tions of this in the descriptions attached to builtin con-
     trol 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.

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ENGINE(3)                    OpenSSL                    ENGINE(3)

      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 argu-
     ment 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 anything. 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,
     numerical-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 control

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ENGINE(3)                    OpenSSL                    ENGINE(3)

     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 symbol, ENGINE_CMD_BASE,
     that all control commands implemented by ENGINEs from. Any
     command value lower than this symbol is considered a "gen-
     eric" command is handled directly by the OpenSSL core rou-
     tines.

     It is using these "core" control commands that one can dis-
     cover 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 "discovery" 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,

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ENGINE(3)                    OpenSSL                    ENGINE(3)

     ENGINE_GET_NEXT_CMD_TYPE takes the identifier of a command
     supported by the ENGINE and returns the next command iden-
     tifier 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 description, or populate a supplied charac-
     ter 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(). "INTER-
     NAL" commands are not intended to be exposed to text-based
     configuration by applications, administrations, users, etc.
     These can support arbitrary operations via ENGINE_ctrl(),
     including 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 determinie
     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_VENDOR_LOGO_GIF" -
     and ENGINE could therefore decide whether or not to support
     this "foo"-specific extension).

     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 independantly of OpenSSL
     libraries and/or OpenSSL-based applications, and would also
     remove any requirement for applications to explicitly use
     the "dynamic" ENGINE to bind to shared-library implementa-
     tions.

SEE ALSO

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

MirOS BSD #10-current      2005-02-05                          14

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