text: /*
   * Written by Geoff Thorpe (geoff@geoffthorpe.net) for the OpenSSL project
   * 2000.
   */
  /* ====================================================================
   * Copyright (c) 1999-2004 The OpenSSL Project.  All rights reserved.
   *
   * Redistribution and use in source and binary forms, with or without
   * modification, are permitted provided that the following conditions
   * are met:
   *
   * 1. Redistributions of source code must retain the above copyright
   *    notice, this list of conditions and the following disclaimer.
   *
   * 2. Redistributions in binary form must reproduce the above copyright
   *    notice, this list of conditions and the following disclaimer in
   *    the documentation and/or other materials provided with the
   *    distribution.
   *
   * 3. All advertising materials mentioning features or use of this
   *    software must display the following acknowledgment:
   *    "This product includes software developed by the OpenSSL Project
   *    for use in the OpenSSL Toolkit. (http://www.OpenSSL.org/)"
   *
   * 4. The names "OpenSSL Toolkit" and "OpenSSL Project" must not be used to
   *    endorse or promote products derived from this software without
   *    prior written permission. For written permission, please contact
   *    licensing@OpenSSL.org.
   *
   * 5. Products derived from this software may not be called "OpenSSL"
   *    nor may "OpenSSL" appear in their names without prior written
   *    permission of the OpenSSL Project.
   *
   * 6. Redistributions of any form whatsoever must retain the following
   *    acknowledgment:
   *    "This product includes software developed by the OpenSSL Project
   *    for use in the OpenSSL Toolkit (http://www.OpenSSL.org/)"
   *
   * THIS SOFTWARE IS PROVIDED BY THE OpenSSL PROJECT ``AS IS'' AND ANY
   * EXPRESSED OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
   * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR
   * PURPOSE ARE DISCLAIMED.  IN NO EVENT SHALL THE OpenSSL PROJECT OR
   * ITS CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
   * SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT
   * NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES;
   * LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
   * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT,
   * STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
   * ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED
   * OF THE POSSIBILITY OF SUCH DAMAGE.
   * ====================================================================
   *
   * This product includes cryptographic software written by Eric Young
   * (eay@cryptsoft.com).  This product includes software written by Tim
   * Hudson (tjh@cryptsoft.com).
   *
   */
  /* ====================================================================
   * Copyright 2002 Sun Microsystems, Inc. ALL RIGHTS RESERVED.
   * ECDH support in OpenSSL originally developed by
   * SUN MICROSYSTEMS, INC., and contributed to the OpenSSL project.
   */
  
  #ifndef HEADER_ENGINE_H
  # define HEADER_ENGINE_H
  
  # include <openssl/opensslconf.h>
  
  # ifdef OPENSSL_NO_ENGINE
  #  error ENGINE is disabled.
  # endif
  
  # if OPENSSL_API_COMPAT < 0x10100000L
  #  include <openssl/bn.h>
  #  ifndef OPENSSL_NO_RSA
  #   include <openssl/rsa.h>
  #  endif
  #  ifndef OPENSSL_NO_DSA
  #   include <openssl/dsa.h>
  #  endif
  #  ifndef OPENSSL_NO_DH
  #   include <openssl/dh.h>
  #  endif
  #  ifndef OPENSSL_NO_EC
  #   include <openssl/ec.h>
  #  endif
  #  include <openssl/rand.h>
  #  include <openssl/ui.h>
  #  include <openssl/err.h>
  # endif
  
  # include <openssl/ossl_typ.h>
  # include <openssl/symhacks.h>
  
  # include <openssl/x509.h>
  
  #ifdef  __cplusplus
  extern "C" {
  #endif
  
  /*
   * These flags are used to control combinations of algorithm (methods) by
   * bitwise "OR"ing.
   */
  # define ENGINE_METHOD_RSA               (unsigned int)0x0001
  # define ENGINE_METHOD_DSA               (unsigned int)0x0002
  # define ENGINE_METHOD_DH                (unsigned int)0x0004
  # define ENGINE_METHOD_RAND              (unsigned int)0x0008
  # define ENGINE_METHOD_CIPHERS           (unsigned int)0x0040
  # define ENGINE_METHOD_DIGESTS           (unsigned int)0x0080
  # define ENGINE_METHOD_PKEY_METHS        (unsigned int)0x0200
  # define ENGINE_METHOD_PKEY_ASN1_METHS   (unsigned int)0x0400
  # define ENGINE_METHOD_EC                (unsigned int)0x0800
  /* Obvious all-or-nothing cases. */
  # define ENGINE_METHOD_ALL               (unsigned int)0xFFFF
  # define ENGINE_METHOD_NONE              (unsigned int)0x0000
  
  /*
   * This(ese) flag(s) controls behaviour of the ENGINE_TABLE mechanism used
   * internally to control registration of ENGINE implementations, and can be
   * set by ENGINE_set_table_flags(). The "NOINIT" flag prevents attempts to
   * initialise registered ENGINEs if they are not already initialised.
   */
  # define ENGINE_TABLE_FLAG_NOINIT        (unsigned int)0x0001
  
  /* ENGINE flags that can be set by ENGINE_set_flags(). */
  /* Not used */
  /* #define ENGINE_FLAGS_MALLOCED        0x0001 */
  
  /*
   * This flag is for ENGINEs that wish to handle the various 'CMD'-related
   * control commands on their own. Without this flag, ENGINE_ctrl() handles
   * these control commands on behalf of the ENGINE using their "cmd_defns"
   * data.
   */
  # define ENGINE_FLAGS_MANUAL_CMD_CTRL    (int)0x0002
  
  /*
   * This flag is for ENGINEs who return new duplicate structures when found
   * via "ENGINE_by_id()". When an ENGINE must store state (eg. if
   * ENGINE_ctrl() commands are called in sequence as part of some stateful
   * process like key-generation setup and execution), it can set this flag -
   * then each attempt to obtain the ENGINE will result in it being copied into
   * a new structure. Normally, ENGINEs don't declare this flag so
   * ENGINE_by_id() just increments the existing ENGINE's structural reference
   * count.
   */
  # define ENGINE_FLAGS_BY_ID_COPY         (int)0x0004
  
  /*
   * This flag if for an ENGINE that does not want its methods registered as
   * part of ENGINE_register_all_complete() for example if the methods are not
   * usable as default methods.
   */
  
  # define ENGINE_FLAGS_NO_REGISTER_ALL    (int)0x0008
  
  /*
   * ENGINEs can support their own command types, and these flags are used in
   * ENGINE_CTRL_GET_CMD_FLAGS to indicate to the caller what kind of input
   * each command expects. Currently only numeric and string input is
   * supported. If a control command supports none of the _NUMERIC, _STRING, or
   * _NO_INPUT options, then it is regarded as an "internal" control command -
   * and not for use in config setting situations. As such, they're not
   * available to the ENGINE_ctrl_cmd_string() function, only raw ENGINE_ctrl()
   * access. Changes to this list of 'command types' should be reflected
   * carefully in ENGINE_cmd_is_executable() and ENGINE_ctrl_cmd_string().
   */
  
  /* accepts a 'long' input value (3rd parameter to ENGINE_ctrl) */
  # define ENGINE_CMD_FLAG_NUMERIC         (unsigned int)0x0001
  /*
   * accepts string input (cast from 'void*' to 'const char *', 4th parameter
   * to ENGINE_ctrl)
   */
  # define ENGINE_CMD_FLAG_STRING          (unsigned int)0x0002
  /*
   * Indicates that the control command takes *no* input. Ie. the control
   * command is unparameterised.
   */
  # define ENGINE_CMD_FLAG_NO_INPUT        (unsigned int)0x0004
  /*
   * Indicates that the control command is internal. This control command won't
   * be shown in any output, and is only usable through the ENGINE_ctrl_cmd()
   * function.
   */
  # define ENGINE_CMD_FLAG_INTERNAL        (unsigned int)0x0008
  
  /*
   * NB: These 3 control commands are deprecated and should not be used.
   * ENGINEs relying on these commands should compile conditional support for
   * compatibility (eg. if these symbols are defined) but should also migrate
   * the same functionality to their own ENGINE-specific control functions that
   * can be "discovered" by calling applications. The fact these control
   * commands wouldn't be "executable" (ie. usable by text-based config)
   * doesn't change the fact that application code can find and use them
   * without requiring per-ENGINE hacking.
   */
  
  /*
   * These flags are used to tell the ctrl function what should be done. All
   * command numbers are shared between all engines, even if some don't make
   * sense to some engines.  In such a case, they do nothing but return the
   * error ENGINE_R_CTRL_COMMAND_NOT_IMPLEMENTED.
   */
  # define ENGINE_CTRL_SET_LOGSTREAM               1
  # define ENGINE_CTRL_SET_PASSWORD_CALLBACK       2
  # define ENGINE_CTRL_HUP                         3/* Close and reinitialise
                                                     * any handles/connections
                                                     * etc. */
  # define ENGINE_CTRL_SET_USER_INTERFACE          4/* Alternative to callback */
  # define ENGINE_CTRL_SET_CALLBACK_DATA           5/* User-specific data, used
                                                     * when calling the password
                                                     * callback and the user
                                                     * interface */
  # define ENGINE_CTRL_LOAD_CONFIGURATION          6/* Load a configuration,
                                                     * given a string that
                                                     * represents a file name
                                                     * or so */
  # define ENGINE_CTRL_LOAD_SECTION                7/* Load data from a given
                                                     * section in the already
                                                     * loaded configuration */
  
  /*
   * These control commands allow an application to deal with an arbitrary
   * engine in a dynamic way. Warn: Negative return values indicate errors FOR
   * THESE COMMANDS because zero is used to indicate 'end-of-list'. Other
   * commands, including ENGINE-specific command types, return zero for an
   * error. An ENGINE can choose to implement these ctrl functions, and can
   * internally manage things however it chooses - it does so by setting the
   * ENGINE_FLAGS_MANUAL_CMD_CTRL flag (using ENGINE_set_flags()). Otherwise
   * the ENGINE_ctrl() code handles this on the ENGINE's behalf using the
   * cmd_defns data (set using ENGINE_set_cmd_defns()). This means an ENGINE's
   * ctrl() handler need only implement its own commands - the above "meta"
   * commands will be taken care of.
   */
  
  /*
   * Returns non-zero if the supplied ENGINE has a ctrl() handler. If "not",
   * then all the remaining control commands will return failure, so it is
   * worth checking this first if the caller is trying to "discover" the
   * engine's capabilities and doesn't want errors generated unnecessarily.
   */
  # define ENGINE_CTRL_HAS_CTRL_FUNCTION           10
  /*
   * Returns a positive command number for the first command supported by the
   * engine. Returns zero if no ctrl commands are supported.
   */
  # define ENGINE_CTRL_GET_FIRST_CMD_TYPE          11
  /*
   * The 'long' argument specifies a command implemented by the engine, and the
   * return value is the next command supported, or zero if there are no more.
   */
  # define ENGINE_CTRL_GET_NEXT_CMD_TYPE           12
  /*
   * The 'void*' argument is a command name (cast from 'const char *'), and the
   * return value is the command that corresponds to it.
   */
  # define ENGINE_CTRL_GET_CMD_FROM_NAME           13
  /*
   * The next two allow a command to be converted into its corresponding string
   * form. In each case, the 'long' argument supplies the command. In the
   * NAME_LEN case, the return value is the length of the command name (not
   * counting a trailing EOL). In the NAME case, the 'void*' argument must be a
   * string buffer large enough, and it will be populated with the name of the
   * command (WITH a trailing EOL).
   */
  # define ENGINE_CTRL_GET_NAME_LEN_FROM_CMD       14
  # define ENGINE_CTRL_GET_NAME_FROM_CMD           15
  /* The next two are similar but give a "short description" of a command. */
  # define ENGINE_CTRL_GET_DESC_LEN_FROM_CMD       16
  # define ENGINE_CTRL_GET_DESC_FROM_CMD           17
  /*
   * With this command, the return value is the OR'd combination of
   * ENGINE_CMD_FLAG_*** values that indicate what kind of input a given
   * engine-specific ctrl command expects.
   */
  # define ENGINE_CTRL_GET_CMD_FLAGS               18
  
  /*
   * ENGINE implementations should start the numbering of their own control
   * commands from this value. (ie. ENGINE_CMD_BASE, ENGINE_CMD_BASE + 1, etc).
   */
  # define ENGINE_CMD_BASE                         200
  
  /*
   * NB: These 2 nCipher "chil" control commands are deprecated, and their
   * functionality is now available through ENGINE-specific control commands
   * (exposed through the above-mentioned 'CMD'-handling). Code using these 2
   * commands should be migrated to the more general command handling before
   * these are removed.
   */
  
  /* Flags specific to the nCipher "chil" engine */
  # define ENGINE_CTRL_CHIL_SET_FORKCHECK          100
          /*
           * Depending on the value of the (long)i argument, this sets or
           * unsets the SimpleForkCheck flag in the CHIL API to enable or
           * disable checking and workarounds for applications that fork().
           */
  # define ENGINE_CTRL_CHIL_NO_LOCKING             101
          /*
           * This prevents the initialisation function from providing mutex
           * callbacks to the nCipher library.
           */
  
  /*
   * If an ENGINE supports its own specific control commands and wishes the
   * framework to handle the above 'ENGINE_CMD_***'-manipulation commands on
   * its behalf, it should supply a null-terminated array of ENGINE_CMD_DEFN
   * entries to ENGINE_set_cmd_defns(). It should also implement a ctrl()
   * handler that supports the stated commands (ie. the "cmd_num" entries as
   * described by the array). NB: The array must be ordered in increasing order
   * of cmd_num. "null-terminated" means that the last ENGINE_CMD_DEFN element
   * has cmd_num set to zero and/or cmd_name set to NULL.
   */
  typedef struct ENGINE_CMD_DEFN_st {
      unsigned int cmd_num;       /* The command number */
      const char *cmd_name;       /* The command name itself */
      const char *cmd_desc;       /* A short description of the command */
      unsigned int cmd_flags;     /* The input the command expects */
  } ENGINE_CMD_DEFN;
  
  /* Generic function pointer */
  typedef int (*ENGINE_GEN_FUNC_PTR) (void);
  /* Generic function pointer taking no arguments */
  typedef int (*ENGINE_GEN_INT_FUNC_PTR) (ENGINE *);
  /* Specific control function pointer */
  typedef int (*ENGINE_CTRL_FUNC_PTR) (ENGINE *, int, long, void *,
                                       void (*f) (void));
  /* Generic load_key function pointer */
  typedef EVP_PKEY *(*ENGINE_LOAD_KEY_PTR)(ENGINE *, const char *,
                                           UI_METHOD *ui_method,
                                           void *callback_data);
  typedef int (*ENGINE_SSL_CLIENT_CERT_PTR) (ENGINE *, SSL *ssl,
                                             STACK_OF(X509_NAME) *ca_dn,
                                             X509 **pcert, EVP_PKEY **pkey,
                                             STACK_OF(X509) **pother,
                                             UI_METHOD *ui_method,
                                             void *callback_data);
  /*-
   * These callback types are for an ENGINE's handler for cipher and digest logic.
   * These handlers have these prototypes;
   *   int foo(ENGINE *e, const EVP_CIPHER **cipher, const int **nids, int nid);
   *   int foo(ENGINE *e, const EVP_MD **digest, const int **nids, int nid);
   * Looking at how to implement these handlers in the case of cipher support, if
   * the framework wants the EVP_CIPHER for 'nid', it will call;
   *   foo(e, &p_evp_cipher, NULL, nid);    (return zero for failure)
   * If the framework wants a list of supported 'nid's, it will call;
   *   foo(e, NULL, &p_nids, 0); (returns number of 'nids' or -1 for error)
   */
  /*
   * Returns to a pointer to the array of supported cipher 'nid's. If the
   * second parameter is non-NULL it is set to the size of the returned array.
   */
  typedef int (*ENGINE_CIPHERS_PTR) (ENGINE *, const EVP_CIPHER **,
                                     const int **, int);
  typedef int (*ENGINE_DIGESTS_PTR) (ENGINE *, const EVP_MD **, const int **,
                                     int);
  typedef int (*ENGINE_PKEY_METHS_PTR) (ENGINE *, EVP_PKEY_METHOD **,
                                        const int **, int);
  typedef int (*ENGINE_PKEY_ASN1_METHS_PTR) (ENGINE *, EVP_PKEY_ASN1_METHOD **,
                                             const int **, int);
  /*
   * STRUCTURE functions ... all of these functions deal with pointers to
   * ENGINE structures where the pointers have a "structural reference". This
   * means that their reference is to allowed access to the structure but it
   * does not imply that the structure is functional. To simply increment or
   * decrement the structural reference count, use ENGINE_by_id and
   * ENGINE_free. NB: This is not required when iterating using ENGINE_get_next
   * as it will automatically decrement the structural reference count of the
   * "current" ENGINE and increment the structural reference count of the
   * ENGINE it returns (unless it is NULL).
   */
  
  /* Get the first/last "ENGINE" type available. */
  ENGINE *ENGINE_get_first(void);
  ENGINE *ENGINE_get_last(void);
  /* Iterate to the next/previous "ENGINE" type (NULL = end of the list). */
  ENGINE *ENGINE_get_next(ENGINE *e);
  ENGINE *ENGINE_get_prev(ENGINE *e);
  /* Add another "ENGINE" type into the array. */
  int ENGINE_add(ENGINE *e);
  /* Remove an existing "ENGINE" type from the array. */
  int ENGINE_remove(ENGINE *e);
  /* Retrieve an engine from the list by its unique "id" value. */
  ENGINE *ENGINE_by_id(const char *id);
  
  #if OPENSSL_API_COMPAT < 0x10100000L
  # define ENGINE_load_openssl() \
      OPENSSL_init_crypto(OPENSSL_INIT_ENGINE_OPENSSL, NULL)
  # define ENGINE_load_dynamic() \
      OPENSSL_init_crypto(OPENSSL_INIT_ENGINE_DYNAMIC, NULL)
  # ifndef OPENSSL_NO_STATIC_ENGINE
  #  define ENGINE_load_padlock() \
      OPENSSL_init_crypto(OPENSSL_INIT_ENGINE_PADLOCK, NULL)
  #  define ENGINE_load_capi() \
      OPENSSL_init_crypto(OPENSSL_INIT_ENGINE_CAPI, NULL)
  #  define ENGINE_load_dasync() \
      OPENSSL_init_crypto(OPENSSL_INIT_ENGINE_DASYNC, NULL)
  #  define ENGINE_load_afalg() \
      OPENSSL_init_crypto(OPENSSL_INIT_ENGINE_AFALG, NULL)
  # endif
  # define ENGINE_load_cryptodev() \
      OPENSSL_init_crypto(OPENSSL_INIT_ENGINE_CRYPTODEV, NULL)
  # define ENGINE_load_rdrand() \
      OPENSSL_init_crypto(OPENSSL_INIT_ENGINE_RDRAND, NULL)
  #endif
  void ENGINE_load_builtin_engines(void);
  
  /*
   * Get and set global flags (ENGINE_TABLE_FLAG_***) for the implementation
   * "registry" handling.
   */
  unsigned int ENGINE_get_table_flags(void);
  void ENGINE_set_table_flags(unsigned int flags);
  
  /*- Manage registration of ENGINEs per "table". For each type, there are 3
   * functions;
   *   ENGINE_register_***(e) - registers the implementation from 'e' (if it has one)
   *   ENGINE_unregister_***(e) - unregister the implementation from 'e'
   *   ENGINE_register_all_***() - call ENGINE_register_***() for each 'e' in the list
   * Cleanup is automatically registered from each table when required, so
   * ENGINE_cleanup() will reverse any "register" operations.
   */
  
  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_EC(ENGINE *e);
  void ENGINE_unregister_EC(ENGINE *e);
  void ENGINE_register_all_EC(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_pkey_meths(ENGINE *e);
  void ENGINE_unregister_pkey_meths(ENGINE *e);
  void ENGINE_register_all_pkey_meths(void);
  
  int ENGINE_register_pkey_asn1_meths(ENGINE *e);
  void ENGINE_unregister_pkey_asn1_meths(ENGINE *e);
  void ENGINE_register_all_pkey_asn1_meths(void);
  
  /*
   * These functions register all support from the above categories. Note, use
   * of these functions can result in static linkage of code your application
   * may not need. If you only need a subset of functionality, consider using
   * more selective initialisation.
   */
  int ENGINE_register_complete(ENGINE *e);
  int ENGINE_register_all_complete(void);
  
  /*
   * Send parametrised control commands to the engine. The possibilities to
   * send down an integer, a pointer to data or a function pointer are
   * provided. Any of the parameters may or may not be NULL, depending on the
   * command number. In actuality, this function only requires a structural
   * (rather than functional) reference to an engine, but many control commands
   * may require the engine be functional. The caller should be aware of trying
   * commands that require an operational ENGINE, and only use functional
   * references in such situations.
   */
  int ENGINE_ctrl(ENGINE *e, int cmd, long i, void *p, void (*f) (void));
  
  /*
   * This function tests if an ENGINE-specific command is usable as a
   * "setting". Eg. in an application's config file that gets processed through
   * ENGINE_ctrl_cmd_string(). If this returns zero, it is not available to
   * ENGINE_ctrl_cmd_string(), only ENGINE_ctrl().
   */
  int ENGINE_cmd_is_executable(ENGINE *e, int cmd);
  
  /*
   * This function works like ENGINE_ctrl() with the exception of taking a
   * command name instead of a command number, and can handle optional
   * commands. See the comment on ENGINE_ctrl_cmd_string() for an explanation
   * on how to use the cmd_name and cmd_optional.
   */
  int ENGINE_ctrl_cmd(ENGINE *e, const char *cmd_name,
                      long i, void *p, void (*f) (void), int cmd_optional);
  
  /*
   * This function passes a command-name and argument to an ENGINE. The
   * cmd_name is converted to a command number and the control command is
   * called using 'arg' as an argument (unless the ENGINE doesn't support such
   * a command, in which case no control command is called). The command is
   * checked for input flags, and if necessary the argument will be converted
   * to a numeric value. If cmd_optional is non-zero, then if the ENGINE
   * doesn't support the given cmd_name the return value will be success
   * anyway. This function is intended for applications to use so that users
   * (or config files) can supply engine-specific config data to the ENGINE at
   * run-time to control behaviour of specific engines. As such, it shouldn't
   * be used for calling ENGINE_ctrl() functions that return data, deal with
   * binary data, or that are otherwise supposed to be used directly through
   * ENGINE_ctrl() in application code. Any "return" data from an ENGINE_ctrl()
   * operation in this function will be lost - the return value is interpreted
   * as failure if the return value is zero, success otherwise, and this
   * function returns a boolean value as a result. In other words, vendors of
   * 'ENGINE'-enabled devices should write ENGINE implementations with
   * parameterisations that work in this scheme, so that compliant ENGINE-based
   * applications can work consistently with the same configuration for the
   * same ENGINE-enabled devices, across applications.
   */
  int ENGINE_ctrl_cmd_string(ENGINE *e, const char *cmd_name, const char *arg,
                             int cmd_optional);
  
  /*
   * These functions are useful for manufacturing new ENGINE structures. They
   * don't address reference counting at all - one uses them to populate an
   * ENGINE structure with personalised implementations of things prior to
   * using it directly or adding it to the builtin ENGINE list in OpenSSL.
   * These are also here so that the ENGINE structure doesn't have to be
   * exposed and break binary compatibility!
   */
  ENGINE *ENGINE_new(void);
  int ENGINE_free(ENGINE *e);
  int ENGINE_up_ref(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_EC(ENGINE *e, const EC_KEY_METHOD *ecdsa_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_load_ssl_client_cert_function(ENGINE *e,
                                               ENGINE_SSL_CLIENT_CERT_PTR
                                               loadssl_f);
  int ENGINE_set_ciphers(ENGINE *e, ENGINE_CIPHERS_PTR f);
  int ENGINE_set_digests(ENGINE *e, ENGINE_DIGESTS_PTR f);
  int ENGINE_set_pkey_meths(ENGINE *e, ENGINE_PKEY_METHS_PTR f);
  int ENGINE_set_pkey_asn1_meths(ENGINE *e, ENGINE_PKEY_ASN1_METHS_PTR f);
  int ENGINE_set_flags(ENGINE *e, int flags);
  int ENGINE_set_cmd_defns(ENGINE *e, const ENGINE_CMD_DEFN *defns);
  /* These functions allow control over any per-structure ENGINE data. */
  #define ENGINE_get_ex_new_index(l, p, newf, dupf, freef) \
      CRYPTO_get_ex_new_index(CRYPTO_EX_INDEX_ENGINE, l, p, newf, dupf, freef)
  int ENGINE_set_ex_data(ENGINE *e, int idx, void *arg);
  void *ENGINE_get_ex_data(const ENGINE *e, int idx);
  
  /*
   * This function cleans up anything that needs it. Eg. the ENGINE_add()
   * function automatically ensures the list cleanup function is registered to
   * be called from ENGINE_cleanup(). Similarly, all ENGINE_register_***
   * functions ensure ENGINE_cleanup() will clean up after them.
   */
  void ENGINE_cleanup(void);
  
  /*
   * These return values from within the ENGINE structure. These can be useful
   * with functional references as well as structural references - it depends
   * which you obtained. Using the result for functional purposes if you only
   * obtained a structural reference may be problematic!
   */
  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 EC_KEY_METHOD *ENGINE_get_EC(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_SSL_CLIENT_CERT_PTR ENGINE_get_ssl_client_cert_function(const ENGINE
                                                                 *e);
  ENGINE_CIPHERS_PTR ENGINE_get_ciphers(const ENGINE *e);
  ENGINE_DIGESTS_PTR ENGINE_get_digests(const ENGINE *e);
  ENGINE_PKEY_METHS_PTR ENGINE_get_pkey_meths(const ENGINE *e);
  ENGINE_PKEY_ASN1_METHS_PTR ENGINE_get_pkey_asn1_meths(const ENGINE *e);
  const EVP_CIPHER *ENGINE_get_cipher(ENGINE *e, int nid);
  const EVP_MD *ENGINE_get_digest(ENGINE *e, int nid);
  const EVP_PKEY_METHOD *ENGINE_get_pkey_meth(ENGINE *e, int nid);
  const EVP_PKEY_ASN1_METHOD *ENGINE_get_pkey_asn1_meth(ENGINE *e, int nid);
  const EVP_PKEY_ASN1_METHOD *ENGINE_get_pkey_asn1_meth_str(ENGINE *e,
                                                            const char *str,
                                                            int len);
  const EVP_PKEY_ASN1_METHOD *ENGINE_pkey_asn1_find_str(ENGINE **pe,
                                                        const char *str,
                                                        int len);
  const ENGINE_CMD_DEFN *ENGINE_get_cmd_defns(const ENGINE *e);
  int ENGINE_get_flags(const ENGINE *e);
  
  /*
   * FUNCTIONAL functions. These functions deal with ENGINE structures that
   * have (or will) be initialised for use. Broadly speaking, the structural
   * functions are useful for iterating the list of available engine types,
   * creating new engine types, and other "list" operations. These functions
   * actually deal with ENGINEs that are to be used. As such these functions
   * can fail (if applicable) when particular engines are unavailable - eg. if
   * a hardware accelerator is not attached or not functioning correctly. Each
   * ENGINE has 2 reference counts; structural and functional. Every time a
   * functional reference is obtained or released, a corresponding structural
   * reference is automatically obtained or released too.
   */
  
  /*
   * Initialise a engine type for use (or up its reference count if it's
   * already in use). This will fail if the engine is not currently operational
   * and cannot initialise.
   */
  int ENGINE_init(ENGINE *e);
  /*
   * Free a functional reference to a engine type. This does not require a
   * corresponding call to ENGINE_free as it also releases a structural
   * reference.
   */
  int ENGINE_finish(ENGINE *e);
  
  /*
   * The following functions handle keys that are stored in some secondary
   * location, handled by the engine.  The storage may be on a card or
   * whatever.
   */
  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);
  int ENGINE_load_ssl_client_cert(ENGINE *e, SSL *s,
                                  STACK_OF(X509_NAME) *ca_dn, X509 **pcert,
                                  EVP_PKEY **ppkey, STACK_OF(X509) **pother,
                                  UI_METHOD *ui_method, void *callback_data);
  
  /*
   * This returns a pointer for the current ENGINE structure that is (by
   * default) performing any RSA operations. The value returned is an
   * incremented reference, so it should be free'd (ENGINE_finish) before it is
   * discarded.
   */
  ENGINE *ENGINE_get_default_RSA(void);
  /* Same for the other "methods" */
  ENGINE *ENGINE_get_default_DSA(void);
  ENGINE *ENGINE_get_default_EC(void);
  ENGINE *ENGINE_get_default_DH(void);
  ENGINE *ENGINE_get_default_RAND(void);
  /*
   * These functions can be used to get a functional reference to perform
   * ciphering or digesting corresponding to "nid".
   */
  ENGINE *ENGINE_get_cipher_engine(int nid);
  ENGINE *ENGINE_get_digest_engine(int nid);
  ENGINE *ENGINE_get_pkey_meth_engine(int nid);
  ENGINE *ENGINE_get_pkey_asn1_meth_engine(int nid);
  
  /*
   * This sets a new default ENGINE structure for performing RSA operations. If
   * the result is non-zero (success) then the ENGINE structure will have had
   * its reference count up'd so the caller should still free their own
   * reference 'e'.
   */
  int ENGINE_set_default_RSA(ENGINE *e);
  int ENGINE_set_default_string(ENGINE *e, const char *def_list);
  /* Same for the other "methods" */
  int ENGINE_set_default_DSA(ENGINE *e);
  int ENGINE_set_default_EC(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_pkey_meths(ENGINE *e);
  int ENGINE_set_default_pkey_asn1_meths(ENGINE *e);
  
  /*
   * The combination "set" - the flags are bitwise "OR"d from the
   * ENGINE_METHOD_*** defines above. As with the "ENGINE_register_complete()"
   * function, this function can result in unnecessary static linkage. If your
   * application requires only specific functionality, consider using more
   * selective functions.
   */
  int ENGINE_set_default(ENGINE *e, unsigned int flags);
  
  void ENGINE_add_conf_module(void);
  
  /* Deprecated functions ... */
  /* int ENGINE_clear_defaults(void); */
  
  /**************************/
  /* DYNAMIC ENGINE SUPPORT */
  /**************************/
  
  /* Binary/behaviour compatibility levels */
  # define OSSL_DYNAMIC_VERSION            (unsigned long)0x00030000
  /*
   * Binary versions older than this are too old for us (whether we're a loader
   * or a loadee)
   */
  # define OSSL_DYNAMIC_OLDEST             (unsigned long)0x00030000
  
  /*
   * When compiling an ENGINE entirely as an external shared library, loadable
   * by the "dynamic" ENGINE, these types are needed. The 'dynamic_fns'
   * structure type provides the calling application's (or library's) error
   * functionality and memory management function pointers to the loaded
   * library. These should be used/set in the loaded library code so that the
   * loading application's 'state' will be used/changed in all operations. The
   * 'static_state' pointer allows the loaded library to know if it shares the
   * same static data as the calling application (or library), and thus whether
   * these callbacks need to be set or not.
   */
  typedef void *(*dyn_MEM_malloc_fn) (size_t, const char *, int);
  typedef void *(*dyn_MEM_realloc_fn) (void *, size_t, const char *, int);
  typedef void (*dyn_MEM_free_fn) (void *, const char *, int);
  typedef struct st_dynamic_MEM_fns {
      dyn_MEM_malloc_fn malloc_fn;
      dyn_MEM_realloc_fn realloc_fn;
      dyn_MEM_free_fn free_fn;
  } dynamic_MEM_fns;
  /*
   * FIXME: Perhaps the memory and locking code (crypto.h) should declare and
   * use these types so we (and any other dependant code) can simplify a bit??
   */
  /* The top-level structure */
  typedef struct st_dynamic_fns {
      void *static_state;
      dynamic_MEM_fns mem_fns;
  } dynamic_fns;
  
  /*
   * The version checking function should be of this prototype. NB: The
   * ossl_version value passed in is the OSSL_DYNAMIC_VERSION of the loading
   * code. If this function returns zero, it indicates a (potential) version
   * incompatibility and the loaded library doesn't believe it can proceed.
   * Otherwise, the returned value is the (latest) version supported by the
   * loading library. The loader may still decide that the loaded code's
   * version is unsatisfactory and could veto the load. The function is
   * expected to be implemented with the symbol name "v_check", and a default
   * implementation can be fully instantiated with
   * IMPLEMENT_DYNAMIC_CHECK_FN().
   */
  typedef unsigned long (*dynamic_v_check_fn) (unsigned long ossl_version);
  # define IMPLEMENT_DYNAMIC_CHECK_FN() \
          OPENSSL_EXPORT unsigned long v_check(unsigned long v); \
          OPENSSL_EXPORT unsigned long v_check(unsigned long v) { \
                  if(v >= OSSL_DYNAMIC_OLDEST) return OSSL_DYNAMIC_VERSION; \
                  return 0; }
  
  /*
   * This function is passed the ENGINE structure to initialise with its own
   * function and command settings. It should not adjust the structural or
   * functional reference counts. If this function returns zero, (a) the load
   * will be aborted, (b) the previous ENGINE state will be memcpy'd back onto
   * the structure, and (c) the shared library will be unloaded. So
   * implementations should do their own internal cleanup in failure
   * circumstances otherwise they could leak. The 'id' parameter, if non-NULL,
   * represents the ENGINE id that the loader is looking for. If this is NULL,
   * the shared library can choose to return failure or to initialise a
   * 'default' ENGINE. If non-NULL, the shared library must initialise only an
   * ENGINE matching the passed 'id'. The function is expected to be
   * implemented with the symbol name "bind_engine". A standard implementation
   * can be instantiated with IMPLEMENT_DYNAMIC_BIND_FN(fn) where the parameter
   * 'fn' is a callback function that populates the ENGINE structure and
   * returns an int value (zero for failure). 'fn' should have prototype;
   * [static] int fn(ENGINE *e, const char *id);
   */
  typedef int (*dynamic_bind_engine) (ENGINE *e, const char *id,
                                      const dynamic_fns *fns);
  # define IMPLEMENT_DYNAMIC_BIND_FN(fn) \
          OPENSSL_EXPORT \
          int bind_engine(ENGINE *e, const char *id, const dynamic_fns *fns); \
          OPENSSL_EXPORT \
          int bind_engine(ENGINE *e, const char *id, const dynamic_fns *fns) { \
                  if(ENGINE_get_static_state() == fns->static_state) goto skip_cbs; \
                  CRYPTO_set_mem_functions(fns->mem_fns.malloc_fn, \
                                           fns->mem_fns.realloc_fn, \
                                           fns->mem_fns.free_fn); \
          skip_cbs: \
                  if(!fn(e,id)) return 0; \
                  return 1; }
  
  /*
   * If the loading application (or library) and the loaded ENGINE library
   * share the same static data (eg. they're both dynamically linked to the
   * same libcrypto.so) we need a way to avoid trying to set system callbacks -
   * this would fail, and for the same reason that it's unnecessary to try. If
   * the loaded ENGINE has (or gets from through the loader) its own copy of
   * the libcrypto static data, we will need to set the callbacks. The easiest
   * way to detect this is to have a function that returns a pointer to some
   * static data and let the loading application and loaded ENGINE compare
   * their respective values.
   */
  void *ENGINE_get_static_state(void);
  
  # if defined(__OpenBSD__) || defined(__FreeBSD__) || defined(HAVE_CRYPTODEV)
  void ENGINE_setup_bsd_cryptodev(void);
  # endif
  
  /* BEGIN ERROR CODES */
  /*
   * The following lines are auto generated by the script mkerr.pl. Any changes
   * made after this point may be overwritten when the script is next run.
   */
  void ERR_load_ENGINE_strings(void);
  
  /* Error codes for the ENGINE functions. */
  
  /* Function codes. */
  # define ENGINE_F_DYNAMIC_CTRL                            180
  # define ENGINE_F_DYNAMIC_GET_DATA_CTX                    181
  # define ENGINE_F_DYNAMIC_LOAD                            182
  # define ENGINE_F_DYNAMIC_SET_DATA_CTX                    183
  # define ENGINE_F_ENGINE_ADD                              105
  # define ENGINE_F_ENGINE_BY_ID                            106
  # define ENGINE_F_ENGINE_CMD_IS_EXECUTABLE                170
  # define ENGINE_F_ENGINE_CTRL                             142
  # define ENGINE_F_ENGINE_CTRL_CMD                         178
  # define ENGINE_F_ENGINE_CTRL_CMD_STRING                  171
  # define ENGINE_F_ENGINE_FINISH                           107
  # define ENGINE_F_ENGINE_FREE_UTIL                        108
  # define ENGINE_F_ENGINE_GET_CIPHER                       185
  # define ENGINE_F_ENGINE_GET_DEFAULT_TYPE                 177
  # define ENGINE_F_ENGINE_GET_DIGEST                       186
  # define ENGINE_F_ENGINE_GET_NEXT                         115
  # define ENGINE_F_ENGINE_GET_PKEY_ASN1_METH               193
  # define ENGINE_F_ENGINE_GET_PKEY_METH                    192
  # define ENGINE_F_ENGINE_GET_PREV                         116
  # define ENGINE_F_ENGINE_INIT                             119
  # define ENGINE_F_ENGINE_LIST_ADD                         120
  # define ENGINE_F_ENGINE_LIST_REMOVE                      121
  # define ENGINE_F_ENGINE_LOAD_PRIVATE_KEY                 150
  # define ENGINE_F_ENGINE_LOAD_PUBLIC_KEY                  151
  # define ENGINE_F_ENGINE_LOAD_SSL_CLIENT_CERT             194
  # define ENGINE_F_ENGINE_NEW                              122
  # define ENGINE_F_ENGINE_REMOVE                           123
  # define ENGINE_F_ENGINE_SET_DEFAULT_STRING               189
  # define ENGINE_F_ENGINE_SET_DEFAULT_TYPE                 126
  # define ENGINE_F_ENGINE_SET_ID                           129
  # define ENGINE_F_ENGINE_SET_NAME                         130
  # define ENGINE_F_ENGINE_TABLE_REGISTER                   184
  # define ENGINE_F_ENGINE_UNLOAD_KEY                       152
  # define ENGINE_F_ENGINE_UNLOCKED_FINISH                  191
  # define ENGINE_F_ENGINE_UP_REF                           190
  # define ENGINE_F_INT_CTRL_HELPER                         172
  # define ENGINE_F_INT_ENGINE_CONFIGURE                    188
  # define ENGINE_F_INT_ENGINE_MODULE_INIT                  187
  # define ENGINE_F_LOG_MESSAGE                             141
  
  /* Reason codes. */
  # define ENGINE_R_ALREADY_LOADED                          100
  # define ENGINE_R_ARGUMENT_IS_NOT_A_NUMBER                133
  # define ENGINE_R_CMD_NOT_EXECUTABLE                      134
  # define ENGINE_R_COMMAND_TAKES_INPUT                     135
  # define ENGINE_R_COMMAND_TAKES_NO_INPUT                  136
  # define ENGINE_R_CONFLICTING_ENGINE_ID                   103
  # define ENGINE_R_CTRL_COMMAND_NOT_IMPLEMENTED            119
  # define ENGINE_R_DH_NOT_IMPLEMENTED                      139
  # define ENGINE_R_DSA_NOT_IMPLEMENTED                     140
  # define ENGINE_R_DSO_FAILURE                             104
  # define ENGINE_R_DSO_NOT_FOUND                           132
  # define ENGINE_R_ENGINES_SECTION_ERROR                   148
  # define ENGINE_R_ENGINE_CONFIGURATION_ERROR              102
  # define ENGINE_R_ENGINE_IS_NOT_IN_LIST                   105
  # define ENGINE_R_ENGINE_SECTION_ERROR                    149
  # define ENGINE_R_FAILED_LOADING_PRIVATE_KEY              128
  # define ENGINE_R_FAILED_LOADING_PUBLIC_KEY               129
  # define ENGINE_R_FINISH_FAILED                           106
  # define ENGINE_R_GET_HANDLE_FAILED                       107
  # define ENGINE_R_ID_OR_NAME_MISSING                      108
  # define ENGINE_R_INIT_FAILED                             109
  # define ENGINE_R_INTERNAL_LIST_ERROR                     110
  # define ENGINE_R_INVALID_ARGUMENT                        143
  # define ENGINE_R_INVALID_CMD_NAME                        137
  # define ENGINE_R_INVALID_CMD_NUMBER                      138
  # define ENGINE_R_INVALID_INIT_VALUE                      151
  # define ENGINE_R_INVALID_STRING                          150
  # define ENGINE_R_NOT_INITIALISED                         117
  # define ENGINE_R_NOT_LOADED                              112
  # define ENGINE_R_NO_CONTROL_FUNCTION                     120
  # define ENGINE_R_NO_INDEX                                144
  # define ENGINE_R_NO_LOAD_FUNCTION                        125
  # define ENGINE_R_NO_REFERENCE                            130
  # define ENGINE_R_NO_SUCH_ENGINE                          116
  # define ENGINE_R_NO_UNLOAD_FUNCTION                      126
  # define ENGINE_R_PROVIDE_PARAMETERS                      113
  # define ENGINE_R_RSA_NOT_IMPLEMENTED                     141
  # define ENGINE_R_UNIMPLEMENTED_CIPHER                    146
  # define ENGINE_R_UNIMPLEMENTED_DIGEST                    147
  # define ENGINE_R_UNIMPLEMENTED_PUBLIC_KEY_METHOD         101
  # define ENGINE_R_VERSION_INCOMPATIBILITY                 145
  
  #ifdef  __cplusplus
  }
  #endif
  #endif
  