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     /xlv3/openssl/0.9.7e-sgipl1/work/0.9.7e-sgipl1/openssl-
     0.9.7e/doc/crypto

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     engine(3)		   15/Dec/2002 (0.9.7e)		     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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	   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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	   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

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	  ENGINE implementation includes the following abstractions;

	   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
	  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 creating
	  new ENGINEs dynamically, iterating across OpenSSL's internal

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	  linked-list of loaded ENGINEs, reading 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, 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
	  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 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
	  cryptographic 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 structural
	  reference, call the ENGINE_init() function. This returns

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	  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
	  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
	  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 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 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 conventional RSA

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	  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 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).
	  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 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
	  implementations are indexed by 'nid', these flags and
	  cached-responses are distinct for each 'nid' value.

	  It is worth illustrating the difference between
	  "registration" 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;

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	   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 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
	  contain any alternative ENGINE code at all. So the first
	  consideration 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 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
	  internal callback registration table so that any ENGINE API
	  functionality that knows it requires cleanup can register
	  its cleanup details to be called during ENGINE_cleanup().

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	  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 callbacks
	  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 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 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 operation,
	  otherwise OpenSSL should use its builtin software as per
	  usual. The following code illustrates how to approach this;

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	   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 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"

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	  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 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
	  applications 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
	  speaking 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 initialise 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.

     Page 11					    (printed 10/20/05)

     engine(3)		   15/Dec/2002 (0.9.7e)		     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
	  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 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
	  control commands supported from a structural reference to
	  any ENGINE. It is first important to note that some control

     Page 12					    (printed 10/20/05)

     engine(3)		   15/Dec/2002 (0.9.7e)		     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
	  "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 "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,

     Page 13					    (printed 10/20/05)

     engine(3)		   15/Dec/2002 (0.9.7e)		     engine(3)

	  ENGINE_GET_NEXT_CMD_TYPE takes the identifier of a command
	  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 description,
	  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(), 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
	  implementations.

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

     Page 14					    (printed 10/20/05)

     engine(3)		   15/Dec/2002 (0.9.7e)		     engine(3)

     Page 15					    (printed 10/20/05)

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