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+=pod
+
+=head1 NAME
+
+engine - ENGINE cryptographic module support
+
+=head1 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);
+
+=head1 DESCRIPTION
+
+These functions create, manipulate, and use cryptographic modules in the
+form of B<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 B<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
+
+=head2 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 B<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
+B<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).
+
+=head3 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 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.
+
+=head3 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 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 B<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.
+
+=head2 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 B<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 implementation in OpenSSL (and will from then on
+behave the way it used to before the ENGINE API existed - for details see
+L<RSA_new_method(3)|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;
+
+ assert(e1 == X);
+ assert(e2 == Y);
+ assert(e3 == X);
+ assert(e4 == Y);
+ assert(e5 == NULL);
+
+=head2 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(). 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.
+
+=head3 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;
+
+ 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);
+
+=head3 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.
+
+=head2 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 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 B<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.
+
+=head3 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 anything. In this case we assume the user is
+only supplying commands specific to the given ENGINE so we set this to
+FALSE.
+
+=head3 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
+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, 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).
+
+=head2 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.
+
+=head1 SEE ALSO
+
+L<rsa(3)|rsa(3)>, L<dsa(3)|dsa(3)>, L<dh(3)|dh(3)>, L<rand(3)|rand(3)>,
+L<RSA_new_method(3)|RSA_new_method(3)>
+
+=cut