NAME
    provider-base - The basic OpenSSL library <-> provider functions

SYNOPSIS
     #include <openssl/core_dispatch.h>

     /*
      * None of these are actual functions, but are displayed like this for
      * the function signatures for functions that are offered as function
      * pointers in OSSL_DISPATCH arrays.
      */

     /* Functions offered by libcrypto to the providers */
     const OSSL_ITEM *core_gettable_params(const OSSL_CORE_HANDLE *handle);
     int core_get_params(const OSSL_CORE_HANDLE *handle, OSSL_PARAM params[]);

     typedef void (*OSSL_thread_stop_handler_fn)(void *arg);
     int core_thread_start(const OSSL_CORE_HANDLE *handle,
                           OSSL_thread_stop_handler_fn handfn,
                           void *arg);

     OPENSSL_CORE_CTX *core_get_libctx(const OSSL_CORE_HANDLE *handle);
     void core_new_error(const OSSL_CORE_HANDLE *handle);
     void core_set_error_debug(const OSSL_CORE_HANDLE *handle,
                               const char *file, int line, const char *func);
     void core_vset_error(const OSSL_CORE_HANDLE *handle,
                          uint32_t reason, const char *fmt, va_list args);

     int core_obj_add_sigid(const OSSL_CORE_HANDLE *prov, const char  *sign_name,
                            const char *digest_name, const char *pkey_name);
     int core_obj_create(const OSSL_CORE_HANDLE *handle, const char *oid,
                         const char *sn, const char *ln);

     /*
      * Some OpenSSL functionality is directly offered to providers via
      * dispatch
      */
     void *CRYPTO_malloc(size_t num, const char *file, int line);
     void *CRYPTO_zalloc(size_t num, const char *file, int line);
     void CRYPTO_free(void *ptr, const char *file, int line);
     void CRYPTO_clear_free(void *ptr, size_t num,
                            const char *file, int line);
     void *CRYPTO_realloc(void *addr, size_t num,
                          const char *file, int line);
     void *CRYPTO_clear_realloc(void *addr, size_t old_num, size_t num,
                                const char *file, int line);
     void *CRYPTO_secure_malloc(size_t num, const char *file, int line);
     void *CRYPTO_secure_zalloc(size_t num, const char *file, int line);
     void CRYPTO_secure_free(void *ptr, const char *file, int line);
     void CRYPTO_secure_clear_free(void *ptr, size_t num,
                                   const char *file, int line);
     int CRYPTO_secure_allocated(const void *ptr);
     void OPENSSL_cleanse(void *ptr, size_t len);

     unsigned char *OPENSSL_hexstr2buf(const char *str, long *buflen);

     OSSL_CORE_BIO *BIO_new_file(const char *filename, const char *mode);
     OSSL_CORE_BIO *BIO_new_membuf(const void *buf, int len);
     int BIO_read_ex(OSSL_CORE_BIO *bio, void *data, size_t data_len,
                     size_t *bytes_read);
     int BIO_write_ex(OSSL_CORE_BIO *bio, const void *data, size_t data_len,
                      size_t *written);
     int BIO_up_ref(OSSL_CORE_BIO *bio);
     int BIO_free(OSSL_CORE_BIO *bio);
     int BIO_vprintf(OSSL_CORE_BIO *bio, const char *format, va_list args);
     int BIO_vsnprintf(char *buf, size_t n, const char *fmt, va_list args);

     void OSSL_SELF_TEST_set_callback(OSSL_LIB_CTX *libctx, OSSL_CALLBACK *cb,
                                      void *cbarg);

     size_t get_entropy(const OSSL_CORE_HANDLE *handle,
                        unsigned char **pout, int entropy,
                        size_t min_len, size_t max_len);
     size_t get_user_entropy(const OSSL_CORE_HANDLE *handle,
                             unsigned char **pout, int entropy,
                             size_t min_len, size_t max_len);
     void cleanup_entropy(const OSSL_CORE_HANDLE *handle,
                          unsigned char *buf, size_t len);
     void cleanup_user_entropy(const OSSL_CORE_HANDLE *handle,
                               unsigned char *buf, size_t len);
     size_t get_nonce(const OSSL_CORE_HANDLE *handle,
                      unsigned char **pout, size_t min_len, size_t max_len,
                      const void *salt, size_t salt_len);
     size_t get_user_nonce(const OSSL_CORE_HANDLE *handle,
                           unsigned char **pout, size_t min_len, size_t max_len,
                           const void *salt, size_t salt_len);
     void cleanup_nonce(const OSSL_CORE_HANDLE *handle,
                        unsigned char *buf, size_t len);
     void cleanup_user_nonce(const OSSL_CORE_HANDLE *handle,
                             unsigned char *buf, size_t len);

     /* Functions for querying the providers in the application library context */
     int provider_register_child_cb(const OSSL_CORE_HANDLE *handle,
                         int (*create_cb)(const OSSL_CORE_HANDLE *provider,
                                          void *cbdata),
                         int (*remove_cb)(const OSSL_CORE_HANDLE *provider,
                                          void *cbdata),
                         int (*global_props_cb)(const char *props, void *cbdata),
                         void *cbdata);
     void provider_deregister_child_cb(const OSSL_CORE_HANDLE *handle);
     const char *provider_name(const OSSL_CORE_HANDLE *prov);
     void *provider_get0_provider_ctx(const OSSL_CORE_HANDLE *prov);
     const OSSL_DISPATCH *provider_get0_dispatch(const OSSL_CORE_HANDLE *prov);
     int provider_up_ref(const OSSL_CORE_HANDLE *prov, int activate);
     int provider_free(const OSSL_CORE_HANDLE *prov, int deactivate);

     /* Functions offered by the provider to libcrypto */
     void provider_teardown(void *provctx);
     const OSSL_ITEM *provider_gettable_params(void *provctx);
     int provider_get_params(void *provctx, OSSL_PARAM params[]);
     const OSSL_ALGORITHM *provider_query_operation(void *provctx,
                                                    int operation_id,
                                                    const int *no_store);
     void provider_unquery_operation(void *provctx, int operation_id,
                                     const OSSL_ALGORITHM *algs);
     const OSSL_ITEM *provider_get_reason_strings(void *provctx);
     int provider_get_capabilities(void *provctx, const char *capability,
                                   OSSL_CALLBACK *cb, void *arg);
     int provider_self_test(void *provctx);

DESCRIPTION
    All "functions" mentioned here are passed as function pointers between
    libcrypto and the provider in OSSL_DISPATCH(3) arrays, in the call of
    the provider initialization function. See "Provider" in provider(7) for
    a description of the initialization function. They are known as
    "upcalls".

    All these "functions" have a corresponding function type definition
    named OSSL_FUNC_{name}_fn, and a helper function to retrieve the
    function pointer from a OSSL_DISPATCH(3) element named OSSL_FUNC_{name}.
    For example, the "function" core_gettable_params() has these:

     typedef OSSL_PARAM *
         (OSSL_FUNC_core_gettable_params_fn)(const OSSL_CORE_HANDLE *handle);
     static ossl_inline OSSL_NAME_core_gettable_params_fn
         OSSL_FUNC_core_gettable_params(const OSSL_DISPATCH *opf);

    OSSL_DISPATCH(3) arrays are indexed by numbers that are provided as
    macros in openssl-core_dispatch.h(7), as follows:

    For *in* (the OSSL_DISPATCH(3) array passed from libcrypto to the
    provider):

     core_gettable_params           OSSL_FUNC_CORE_GETTABLE_PARAMS
     core_get_params                OSSL_FUNC_CORE_GET_PARAMS
     core_thread_start              OSSL_FUNC_CORE_THREAD_START
     core_get_libctx                OSSL_FUNC_CORE_GET_LIBCTX
     core_new_error                 OSSL_FUNC_CORE_NEW_ERROR
     core_set_error_debug           OSSL_FUNC_CORE_SET_ERROR_DEBUG
     core_vset_error                OSSL_FUNC_CORE_VSET_ERROR
     core_set_error_mark            OSSL_FUNC_CORE_SET_ERROR_MARK
     core_clear_last_error_mark     OSSL_FUNC_CORE_CLEAR_LAST_ERROR_MARK
     core_pop_error_to_mark         OSSL_FUNC_CORE_POP_ERROR_TO_MARK
     core_count_to_mark             OSSL_FUNC_CORE_COUNT_TO_MARK
     core_obj_add_sigid             OSSL_FUNC_CORE_OBJ_ADD_SIGID
     core_obj_create                OSSL_FUNC_CORE_OBJ_CREATE
     CRYPTO_malloc                  OSSL_FUNC_CRYPTO_MALLOC
     CRYPTO_zalloc                  OSSL_FUNC_CRYPTO_ZALLOC
     CRYPTO_free                    OSSL_FUNC_CRYPTO_FREE
     CRYPTO_clear_free              OSSL_FUNC_CRYPTO_CLEAR_FREE
     CRYPTO_realloc                 OSSL_FUNC_CRYPTO_REALLOC
     CRYPTO_clear_realloc           OSSL_FUNC_CRYPTO_CLEAR_REALLOC
     CRYPTO_secure_malloc           OSSL_FUNC_CRYPTO_SECURE_MALLOC
     CRYPTO_secure_zalloc           OSSL_FUNC_CRYPTO_SECURE_ZALLOC
     CRYPTO_secure_free             OSSL_FUNC_CRYPTO_SECURE_FREE
     CRYPTO_secure_clear_free       OSSL_FUNC_CRYPTO_SECURE_CLEAR_FREE
     CRYPTO_secure_allocated        OSSL_FUNC_CRYPTO_SECURE_ALLOCATED
     BIO_new_file                   OSSL_FUNC_BIO_NEW_FILE
     BIO_new_mem_buf                OSSL_FUNC_BIO_NEW_MEMBUF
     BIO_read_ex                    OSSL_FUNC_BIO_READ_EX
     BIO_write_ex                   OSSL_FUNC_BIO_WRITE_EX
     BIO_up_ref                     OSSL_FUNC_BIO_UP_REF
     BIO_free                       OSSL_FUNC_BIO_FREE
     BIO_vprintf                    OSSL_FUNC_BIO_VPRINTF
     BIO_vsnprintf                  OSSL_FUNC_BIO_VSNPRINTF
     BIO_puts                       OSSL_FUNC_BIO_PUTS
     BIO_gets                       OSSL_FUNC_BIO_GETS
     BIO_ctrl                       OSSL_FUNC_BIO_CTRL
     OPENSSL_cleanse                OSSL_FUNC_OPENSSL_CLEANSE
     OSSL_SELF_TEST_set_callback    OSSL_FUNC_SELF_TEST_CB
     ossl_rand_get_entropy          OSSL_FUNC_GET_ENTROPY
     ossl_rand_get_user_entropy     OSSL_FUNC_GET_USER_ENTROPY
     ossl_rand_cleanup_entropy      OSSL_FUNC_CLEANUP_ENTROPY
     ossl_rand_cleanup_user_entropy OSSL_FUNC_CLEANUP_USER_ENTROPY
     ossl_rand_get_nonce            OSSL_FUNC_GET_NONCE
     ossl_rand_get_user_nonce       OSSL_FUNC_GET_USER_NONCE
     ossl_rand_cleanup_nonce        OSSL_FUNC_CLEANUP_NONCE
     ossl_rand_cleanup_user_nonce   OSSL_FUNC_CLEANUP_USER_NONCE
     provider_register_child_cb     OSSL_FUNC_PROVIDER_REGISTER_CHILD_CB
     provider_deregister_child_cb   OSSL_FUNC_PROVIDER_DEREGISTER_CHILD_CB
     provider_name                  OSSL_FUNC_PROVIDER_NAME
     provider_get0_provider_ctx     OSSL_FUNC_PROVIDER_GET0_PROVIDER_CTX
     provider_get0_dispatch         OSSL_FUNC_PROVIDER_GET0_DISPATCH
     provider_up_ref                OSSL_FUNC_PROVIDER_UP_REF
     provider_free                  OSSL_FUNC_PROVIDER_FREE

    For **out* (the OSSL_DISPATCH(3) array passed from the provider to
    libcrypto):

     provider_teardown              OSSL_FUNC_PROVIDER_TEARDOWN
     provider_gettable_params       OSSL_FUNC_PROVIDER_GETTABLE_PARAMS
     provider_get_params            OSSL_FUNC_PROVIDER_GET_PARAMS
     provider_query_operation       OSSL_FUNC_PROVIDER_QUERY_OPERATION
     provider_unquery_operation     OSSL_FUNC_PROVIDER_UNQUERY_OPERATION
     provider_get_reason_strings    OSSL_FUNC_PROVIDER_GET_REASON_STRINGS
     provider_get_capabilities      OSSL_FUNC_PROVIDER_GET_CAPABILITIES
     provider_self_test             OSSL_FUNC_PROVIDER_SELF_TEST

  Core functions
    core_gettable_params() returns a constant array of descriptor
    OSSL_PARAM(3), for parameters that core_get_params() can handle.

    core_get_params() retrieves parameters from the core for the given
    *handle*. See "Core parameters" below for a description of currently
    known parameters.

    The core_thread_start() function informs the core that the provider has
    stated an interest in the current thread. The core will inform the
    provider when the thread eventually stops. It must be passed the
    *handle* for this provider, as well as a callback *handfn* which will be
    called when the thread stops. The callback will subsequently be called,
    with the supplied argument *arg*, from the thread that is stopping and
    gets passed the provider context as an argument. This may be useful to
    perform thread specific clean up such as freeing thread local variables.

    core_get_libctx() retrieves the core context in which the library object
    for the current provider is stored, accessible through the *handle*.
    This function is useful only for built-in providers such as the default
    provider. Never cast this to OSSL_LIB_CTX in a provider that is not
    built-in as the OSSL_LIB_CTX of the library loading the provider might
    be a completely different structure than the OSSL_LIB_CTX of the library
    the provider is linked to. Use OSSL_LIB_CTX_new_child(3) instead to
    obtain a proper library context that is linked to the application
    library context.

    core_new_error(), core_set_error_debug() and core_vset_error() are
    building blocks for reporting an error back to the core, with reference
    to the *handle*.

    core_new_error()
        allocates a new thread specific error record.

        This corresponds to the OpenSSL function ERR_new(3).

    core_set_error_debug()
        sets debugging information in the current thread specific error
        record. The debugging information includes the name of the file
        *file*, the line *line* and the function name *func* where the error
        occurred.

        This corresponds to the OpenSSL function ERR_set_debug(3).

    core_vset_error()
        sets the *reason* for the error, along with any addition data. The
        *reason* is a number defined by the provider and used to index the
        reason strings table that's returned by
        provider_get_reason_strings(). The additional data is given as a
        format string *fmt* and a set of arguments *args*, which are treated
        in the same manner as with BIO_vsnprintf(). *file* and *line* may
        also be passed to indicate exactly where the error occurred or was
        reported.

        This corresponds to the OpenSSL function ERR_vset_error(3).

    core_set_error_mark()
        sets a mark on the current topmost error record if there is one.

        This corresponds to the OpenSSL function ERR_set_mark(3).

    core_clear_last_error_mark()
        removes the last mark added if there is one.

        This corresponds to the OpenSSL function ERR_clear_last_mark(3).

    core_pop_error_to_mark()
        pops the top of the error stack until a mark is found. The mark is
        then removed. If there is no mark, the whole stack is removed.

        This corresponds to the OpenSSL function ERR_pop_to_mark(3).

    core_count_to_mark()
        returns the number of entries on the error stack above the most
        recently marked entry, not including that entry. If there is no mark
        in the error stack, the number of entries in the error stack is
        returned.

        This corresponds to the OpenSSL function ERR_count_to_mark(3).

    The core_obj_create() function registers a new OID and associated short
    name *sn* and long name *ln* for the given *handle*. It is similar to
    the OpenSSL function OBJ_create(3) except that it returns 1 on success
    or 0 on failure. It will treat as success the case where the OID already
    exists (even if the short name *sn* or long name *ln* provided as
    arguments differ from those associated with the existing OID, in which
    case the new names are not associated).

    The core_obj_add_sigid() function registers a new composite signature
    algorithm (*sign_name*) consisting of an underlying signature algorithm
    (*pkey_name*) and digest algorithm (*digest_name*) for the given
    *handle*. It assumes that the OIDs for the composite signature algorithm
    as well as for the underlying signature and digest algorithms are either
    already known to OpenSSL or have been registered via a call to
    core_obj_create(). It corresponds to the OpenSSL function
    OBJ_add_sigid(3), except that the objects are identified by name rather
    than a numeric NID. Any name (OID, short name or long name) can be used
    to identify the object. It will treat as success the case where the
    composite signature algorithm already exists (even if registered against
    a different underlying signature or digest algorithm). For
    *digest_name*, NULL or an empty string is permissible for signature
    algorithms that do not need a digest to operate correctly. The function
    returns 1 on success or 0 on failure.

    CRYPTO_malloc(), CRYPTO_zalloc(), CRYPTO_free(), CRYPTO_clear_free(),
    CRYPTO_realloc(), CRYPTO_clear_realloc(), CRYPTO_secure_malloc(),
    CRYPTO_secure_zalloc(), CRYPTO_secure_free(),
    CRYPTO_secure_clear_free(), CRYPTO_secure_allocated(), BIO_new_file(),
    BIO_new_mem_buf(), BIO_read_ex(), BIO_write_ex(), BIO_up_ref(),
    BIO_free(), BIO_vprintf(), BIO_vsnprintf(), BIO_gets(), BIO_puts(),
    BIO_ctrl(), OPENSSL_cleanse() and OPENSSL_hexstr2buf() correspond
    exactly to the public functions with the same name. As a matter of fact,
    the pointers in the OSSL_DISPATCH(3) array are typically direct pointers
    to those public functions. Note that the BIO functions take an
    OSSL_CORE_BIO type rather than the standard BIO type. This is to ensure
    that a provider does not mix BIOs from the core with BIOs used on the
    provider side (the two are not compatible).
    OSSL_SELF_TEST_set_callback() is used to set an optional callback that
    can be passed into a provider. This may be ignored by a provider.

    get_entropy() retrieves seeding material from the operating system. The
    seeding material will have at least *entropy* bytes of randomness and
    the output will have at least *min_len* and at most *max_len* bytes. The
    buffer address is stored in **pout* and the buffer length is returned to
    the caller. On error, zero is returned.

    get_user_entropy() is the same as get_entropy() except that it will
    attempt to gather seed material via the seed source specified by a call
    to RAND_set_seed_source_type(3) or via "Random Configuration" in
    config(5).

    cleanup_entropy() is used to clean up and free the buffer returned by
    get_entropy(). The entropy pointer returned by get_entropy() is passed
    in buf and its length in len.

    cleanup_user_entropy() is used to clean up and free the buffer returned
    by get_user_entropy(). The entropy pointer returned by
    get_user_entropy() is passed in buf and its length in len.

    get_nonce() retrieves a nonce using the passed *salt* parameter of
    length *salt_len* and operating system specific information. The *salt*
    should contain uniquely identifying information and this is included, in
    an unspecified manner, as part of the output. The output is stored in a
    buffer which contains at least *min_len* and at most *max_len* bytes.
    The buffer address is stored in **pout* and the buffer length returned
    to the caller. On error, zero is returned.

    get_user_nonce() is the same as get_nonce() except that it will attempt
    to gather seed material via the seed source specified by a call to
    RAND_set_seed_source_type(3) or via "Random Configuration" in config(5).

    cleanup_nonce() is used to clean up and free the buffer returned by
    get_nonce(). The nonce pointer returned by get_nonce() is passed in buf
    and its length in len.

    cleanup_user_nonce() is used to clean up and free the buffer returned by
    get_user_nonce(). The nonce pointer returned by get_user_nonce() is
    passed in buf and its length in len.

    provider_register_child_cb() registers callbacks for being informed
    about the loading and unloading of providers in the application's
    library context. *handle* is this provider's handle and *cbdata* is this
    provider's data that will be passed back to the callbacks. It returns 1
    on success or 0 otherwise. These callbacks may be called while holding
    locks in libcrypto. In order to avoid deadlocks the callback
    implementation must not be long running and must not call other OpenSSL
    API functions or upcalls.

    *create_cb* is a callback that will be called when a new provider is
    loaded into the application's library context. It is also called for any
    providers that are already loaded at the point that this callback is
    registered. The callback is passed the handle being used for the new
    provider being loadded and this provider's data in *cbdata*. It should
    return 1 on success or 0 on failure.

    *remove_cb* is a callback that will be called when a new provider is
    unloaded from the application's library context. It is passed the handle
    being used for the provider being unloaded and this provider's data in
    *cbdata*. It should return 1 on success or 0 on failure.

    *global_props_cb* is a callback that will be called when the global
    properties from the parent library context are changed. It should return
    1 on success or 0 on failure.

    provider_deregister_child_cb() unregisters callbacks previously
    registered via provider_register_child_cb(). If
    provider_register_child_cb() has been called then
    provider_deregister_child_cb() should be called at or before the point
    that this provider's teardown function is called.

    provider_name() returns a string giving the name of the provider
    identified by *handle*.

    provider_get0_provider_ctx() returns the provider context that is
    associated with the provider identified by *prov*.

    provider_get0_dispatch() gets the dispatch table registered by the
    provider identified by *prov* when it initialised.

    provider_up_ref() increments the reference count on the provider *prov*.
    If *activate* is nonzero then the provider is also loaded if it is not
    already loaded. It returns 1 on success or 0 on failure.

    provider_free() decrements the reference count on the provider *prov*.
    If *deactivate* is nonzero then the provider is also unloaded if it is
    not already loaded. It returns 1 on success or 0 on failure.

  Provider functions
    provider_teardown() is called when a provider is shut down and removed
    from the core's provider store. It must free the passed *provctx*.

    provider_gettable_params() should return a constant array of descriptor
    OSSL_PARAM(3), for parameters that provider_get_params() can handle.

    provider_get_params() should process the OSSL_PARAM(3) array *params*,
    setting the values of the parameters it understands.

    provider_query_operation() should return a constant OSSL_ALGORITHM(3)
    that corresponds to the given *operation_id*. It should indicate if the
    core may store a reference to this array by setting **no_store* to 0
    (core may store a reference) or 1 (core may not store a reference).

    provider_unquery_operation() informs the provider that the result of a
    provider_query_operation() is no longer directly required and that the
    function pointers have been copied. The *operation_id* should match that
    passed to provider_query_operation() and *algs* should be its return
    value.

    provider_get_reason_strings() should return a constant OSSL_ITEM(3)
    array that provides reason strings for reason codes the provider may use
    when reporting errors using core_put_error().

    The provider_get_capabilities() function should call the callback *cb*
    passing it a set of OSSL_PARAM(3)s and the caller supplied argument
    *arg*. The OSSL_PARAM(3)s should provide details about the capability
    with the name given in the *capability* argument relevant for the
    provider context *provctx*. If a provider supports multiple capabilities
    with the given name then it may call the callback multiple times (one
    for each capability). Capabilities can be useful for describing the
    services that a provider can offer. For further details see the
    "CAPABILITIES" section below. It should return 1 on success or 0 on
    error.

    The provider_self_test() function should perform known answer tests on a
    subset of the algorithms that it uses, and may also verify the integrity
    of the provider module. It should return 1 on success or 0 on error. It
    will return 1 if this function is not used.

    None of these functions are mandatory, but a provider is fairly useless
    without at least provider_query_operation(), and
    provider_gettable_params() is fairly useless if not accompanied by
    provider_get_params().

  Provider parameters
    provider_get_params() can return the following provider parameters to
    the core:

    "name" (OSSL_PROV_PARAM_NAME) <UTF8 ptr>
        This points to a string that should give a unique name for the
        provider.

    "version" (OSSL_PROV_PARAM_VERSION) <UTF8 ptr>
        This points to a string that is a version number associated with
        this provider. OpenSSL in-built providers use OPENSSL_VERSION_STR,
        but this may be different for any third party provider. This string
        is for informational purposes only.

    "buildinfo" (OSSL_PROV_PARAM_BUILDINFO) <UTF8 ptr>
        This points to a string that is a build information associated with
        this provider. OpenSSL in-built providers use
        OPENSSL_FULL_VERSION_STR, but this may be different for any third
        party provider.

    "status" (OSSL_PROV_PARAM_STATUS) <unsigned integer>
        This returns 0 if the provider has entered an error state, otherwise
        it returns 1.

    provider_gettable_params() should return the above parameters.

  Core parameters
    core_get_params() can retrieve the following core parameters for each
    provider:

    "openssl-version" (OSSL_PROV_PARAM_CORE_VERSION) <UTF8 string ptr>
        This points to the OpenSSL libraries' full version string, i.e. the
        string expanded from the macro OPENSSL_VERSION_STR.

    "provider-name" (OSSL_PROV_PARAM_CORE_PROV_NAME) <UTF8 string ptr>
        This points to the OpenSSL libraries' idea of what the calling
        provider is named.

    "module-filename" (OSSL_PROV_PARAM_CORE_MODULE_FILENAME) <UTF8 string
    ptr>
        This points to a string containing the full filename of the
        providers module file.

    Additionally, provider specific configuration parameters from the config
    file are available, in dotted name form. The dotted name form is a
    concatenation of section names and final config command name separated
    by periods.

    For example, let's say we have the following config example:

     config_diagnostics = 1
     openssl_conf = openssl_init

     [openssl_init]
     providers = providers_sect

     [providers_sect]
     foo = foo_sect

     [foo_sect]
     activate = 1
     data1 = 2
     data2 = str
     more = foo_more

     [foo_more]
     data3 = foo,bar

    The provider will have these additional parameters available:

    "activate"
        pointing at the string "1"

    "data1"
        pointing at the string "2"

    "data2"
        pointing at the string "str"

    "more.data3"
        pointing at the string "foo,bar"

    For more information on handling parameters, see OSSL_PARAM(3) as
    OSSL_PARAM_int(3).

CAPABILITIES
    Capabilities describe some of the services that a provider can offer.
    Applications can query the capabilities to discover those services.

   "TLS-GROUP" Capability
    The "TLS-GROUP" capability can be queried by libssl to discover the list
    of TLS groups that a provider can support. Each group supported can be
    used for *key exchange* (KEX) or *key encapsulation method* (KEM) during
    a TLS handshake. TLS clients can advertise the list of TLS groups they
    support in the supported_groups extension, and TLS servers can select a
    group from the offered list that they also support. In this way a
    provider can add to the list of groups that libssl already supports with
    additional ones.

    Each TLS group that a provider supports should be described via the
    callback passed in through the provider_get_capabilities function. Each
    group should have the following details supplied (all are mandatory,
    except OSSL_CAPABILITY_TLS_GROUP_IS_KEM):

    "tls-group-name" (OSSL_CAPABILITY_TLS_GROUP_NAME) <UTF8 string>
        The name of the group as given in the IANA TLS Supported Groups
        registry
        <https://www.iana.org/assignments/tls-parameters/tls-parameters.xhtm
        l#tls-parameters-8>.

    "tls-group-name-internal" (OSSL_CAPABILITY_TLS_GROUP_NAME_INTERNAL)
    <UTF8 string>
        The name of the group as known by the provider. This could be the
        same as the "tls-group-name", but does not have to be.

    "tls-group-id" (OSSL_CAPABILITY_TLS_GROUP_ID) <unsigned integer>
        The TLS group id value as given in the IANA TLS Supported Groups
        registry.

        It is possible to register the same group id from within different
        providers. Users should note that if no property query is specified,
        or more than one implementation matches the property query then it
        is unspecified which implementation for a particular group id will
        be used.

    "tls-group-alg" (OSSL_CAPABILITY_TLS_GROUP_ALG) <UTF8 string>
        The name of a Key Management algorithm that the provider offers and
        that should be used with this group. Keys created should be able to
        support *key exchange* or *key encapsulation method* (KEM), as
        implied by the optional OSSL_CAPABILITY_TLS_GROUP_IS_KEM flag. The
        algorithm must support key and parameter generation as well as the
        key/parameter generation parameter, OSSL_PKEY_PARAM_GROUP_NAME. The
        group name given via "tls-group-name-internal" above will be passed
        via OSSL_PKEY_PARAM_GROUP_NAME when libssl wishes to generate
        keys/parameters.

    "tls-group-sec-bits" (OSSL_CAPABILITY_TLS_GROUP_SECURITY_BITS) <unsigned
    integer>
        The number of bits of security offered by keys in this group. The
        number of bits should be comparable with the ones given in table 2
        and 3 of the NIST SP800-57 document.

    "tls-group-is-kem" (OSSL_CAPABILITY_TLS_GROUP_IS_KEM) <unsigned integer>
        Boolean flag to describe if the group should be used in *key
        exchange* (KEX) mode (0, default) or in *key encapsulation method*
        (KEM) mode (1).

        This parameter is optional: if not specified, KEX mode is assumed as
        the default mode for the group.

        In KEX mode, in a typical Diffie-Hellman fashion, both sides execute
        *keygen* then *derive* against the peer public key. To operate in
        KEX mode, the group implementation must support the provider
        functions as described in provider-keyexch(7).

        In KEM mode, the client executes *keygen* and sends its public key,
        the server executes *encapsulate* using the client's public key and
        sends back the resulting *ciphertext*, finally the client executes
        *decapsulate* to retrieve the same *shared secret* generated by the
        server's *encapsulate*. To operate in KEM mode, the group
        implementation must support the provider functions as described in
        provider-kem(7).

        Both in KEX and KEM mode, the resulting *shared secret* is then used
        according to the protocol specification.

    "tls-min-tls" (OSSL_CAPABILITY_TLS_GROUP_MIN_TLS) <integer>
    "tls-max-tls" (OSSL_CAPABILITY_TLS_GROUP_MAX_TLS) <integer>
    "tls-min-dtls" (OSSL_CAPABILITY_TLS_GROUP_MIN_DTLS) <integer>
    "tls-max-dtls" (OSSL_CAPABILITY_TLS_GROUP_MAX_DTLS) <integer>
        These parameters can be used to describe the minimum and maximum TLS
        and DTLS versions supported by the group. The values equate to the
        on-the-wire encoding of the various TLS versions. For example
        TLSv1.3 is 0x0304 (772 decimal), and TLSv1.2 is 0x0303 (771
        decimal). A 0 indicates that there is no defined minimum or maximum.
        A -1 indicates that the group should not be used in that protocol.

   "TLS-SIGALG" Capability
    The "TLS-SIGALG" capability can be queried by libssl to discover the
    list of TLS signature algorithms that a provider can support. Each
    signature supported can be used for client- or server-authentication in
    addition to the built-in signature algorithms. TLS1.3 clients can
    advertise the list of TLS signature algorithms they support in the
    signature_algorithms extension, and TLS servers can select an algorithm
    from the offered list that they also support. In this way a provider can
    add to the list of signature algorithms that libssl already supports
    with additional ones.

    Each TLS signature algorithm that a provider supports should be
    described via the callback passed in through the
    provider_get_capabilities function. Each algorithm can have the
    following details supplied:

    "iana-name" (OSSL_CAPABILITY_TLS_SIGALG_IANA_NAME) <UTF8 string>
        The name of the signature algorithm as given in the IANA TLS
        Signature Scheme registry as "Description":
        <https://www.iana.org/assignments/tls-parameters/tls-parameters.xhtm
        l#tls-signaturescheme>. This value must be supplied.

    "iana-code-point" (OSSL_CAPABILITY_TLS_SIGALG_CODE_POINT) <unsigned
    integer>
        The TLS algorithm ID value as given in the IANA TLS SignatureScheme
        registry. This value must be supplied.

        It is possible to register the same code point from within different
        providers. Users should note that if no property query is specified,
        or more than one implementation matches the property query then it
        is unspecified which implementation for a particular code point will
        be used.

    "sigalg-name" (OSSL_CAPABILITY_TLS_SIGALG_NAME) <UTF8 string>
        A name for the full (possibly composite hash-and-signature)
        signature algorithm. The provider may, but is not obligated to,
        provide a signature implementation with this name; if it doesn't,
        this is assumed to be a composite of a pure signature algorithm and
        a hash algorithm, which must be given with the parameters "sig-name"
        and "hash-name". This value must be supplied.

    "sigalg-oid" (OSSL_CAPABILITY_TLS_SIGALG_OID) <UTF8 string>
        The OID of the "sigalg-name" algorithm in canonical numeric text
        form. If this parameter is given, OBJ_create() will be used to
        create an OBJ and a NID for this OID, using the "sigalg-name"
        parameter for its (short) name. Otherwise, it's assumed to already
        exist in the object database, possibly done by the provider with the
        core_obj_create() upcall. This value is optional.

    "sig-name" (OSSL_CAPABILITY_TLS_SIGALG_SIG_NAME) <UTF8 string>
        The name of the pure signature algorithm that is part of a composite
        "sigalg-name". If "sigalg-name" is implemented by the provider, this
        parameter is redundant and must not be given. This value is
        optional.

    "sig-oid" (OSSL_CAPABILITY_TLS_SIGALG_SIG_OID) <UTF8 string>
        The OID of the "sig-name" algorithm in canonical numeric text form.
        If this parameter is given, OBJ_create() will be used to create an
        OBJ and a NID for this OID, using the "sig-name" parameter for its
        (short) name. Otherwise, it is assumed to already exist in the
        object database. This can be done by the provider using the
        core_obj_create() upcall. This value is optional.

    "hash-name" (OSSL_CAPABILITY_TLS_SIGALG_HASH_NAME) <UTF8 string>
        The name of the hash algorithm that is part of a composite
        "sigalg-name". If "sigalg-name" is implemented by the provider, this
        parameter is redundant and must not be given. This value is
        optional.

    "hash-oid" (OSSL_CAPABILITY_TLS_SIGALG_HASH_OID) <UTF8 string>
        The OID of the "hash-name" algorithm in canonical numeric text form.
        If this parameter is given, OBJ_create() will be used to create an
        OBJ and a NID for this OID, using the "hash-name" parameter for its
        (short) name. Otherwise, it's assumed to already exist in the object
        database, possibly done by the provider with the core_obj_create()
        upcall. This value is optional.

    "key-type" (OSSL_CAPABILITY_TLS_SIGALG_KEYTYPE) <UTF8 string>
        The key type of the public key of applicable certificates. If this
        parameter isn't present, it's assumed to be the same as "sig-name"
        if that's present, otherwise "sigalg-name". This value is optional.

    "key-type-oid" (OSSL_CAPABILITY_TLS_SIGALG_KEYTYPE_OID) <UTF8 string>
        The OID of the "key-type" in canonical numeric text form. If this
        parameter is given, OBJ_create() will be used to create an OBJ and a
        NID for this OID, using the "key-type" parameter for its (short)
        name. Otherwise, it's assumed to already exist in the object
        database, possibly done by the provider with the core_obj_create()
        upcall. This value is optional.

    "sec-bits" (OSSL_CAPABILITY_TLS_SIGALG_SECURITY_BITS) <unsigned integer>
        The number of bits of security offered by keys of this algorithm.
        The number of bits should be comparable with the ones given in table
        2 and 3 of the NIST SP800-57 document. This number is used to
        determine the security strength of the algorithm if no digest
        algorithm has been registered that otherwise defines the security
        strength. If the signature algorithm implements its own digest
        internally, this value needs to be set to properly reflect the
        overall security strength. This value must be supplied.

    "tls-min-tls" (OSSL_CAPABILITY_TLS_SIGALG_MIN_TLS) <integer>
    "tls-max-tls" (OSSL_CAPABILITY_TLS_SIGALG_MAX_TLS) <integer>
    "tls-min-dtls" (OSSL_CAPABILITY_TLS_SIGALG_MIN_DTLS) <integer>
    "tls-max-dtls" (OSSL_CAPABILITY_TLS_SIGALG_MAX_DTLS) <integer>
        These parameters can be used to describe the minimum and maximum TLS
        and DTLS versions supported by the signature algorithm. The values
        equate to the on-the-wire encoding of the various TLS versions. For
        example TLSv1.3 is 0x0304 (772 decimal), and TLSv1.2 is 0x0303 (771
        decimal). A 0 indicates that there is no defined minimum or maximum.
        A -1 in either the min or max field indicates that the signature
        algorithm should not be used in that protocol. Presently, provider
        signature algorithms are used only with TLS 1.3, if that's enclosed
        in the specified range.

NOTES
    The core_obj_create() and core_obj_add_sigid() functions were not thread
    safe in OpenSSL 3.0.

EXAMPLES
    This is an example of a simple provider made available as a dynamically
    loadable module. It implements the fictitious algorithm "FOO" for the
    fictitious operation "BAR".

     #include <malloc.h>
     #include <openssl/core.h>
     #include <openssl/core_dispatch.h>

     /* Errors used in this provider */
     #define E_MALLOC       1

     static const OSSL_ITEM reasons[] = {
         { E_MALLOC, "memory allocation failure" }.
         OSSL_DISPATCH_END
     };

     /*
      * To ensure we get the function signature right, forward declare
      * them using function types provided by openssl/core_dispatch.h
      */
     OSSL_FUNC_bar_newctx_fn foo_newctx;
     OSSL_FUNC_bar_freectx_fn foo_freectx;
     OSSL_FUNC_bar_init_fn foo_init;
     OSSL_FUNC_bar_update_fn foo_update;
     OSSL_FUNC_bar_final_fn foo_final;

     OSSL_FUNC_provider_query_operation_fn p_query;
     OSSL_FUNC_provider_get_reason_strings_fn p_reasons;
     OSSL_FUNC_provider_teardown_fn p_teardown;

     OSSL_provider_init_fn OSSL_provider_init;

     OSSL_FUNC_core_put_error *c_put_error = NULL;

     /* Provider context */
     struct prov_ctx_st {
         OSSL_CORE_HANDLE *handle;
     }

     /* operation context for the algorithm FOO */
     struct foo_ctx_st {
         struct prov_ctx_st *provctx;
         int b;
     };

     static void *foo_newctx(void *provctx)
     {
         struct foo_ctx_st *fooctx = malloc(sizeof(*fooctx));

         if (fooctx != NULL)
             fooctx->provctx = provctx;
         else
             c_put_error(provctx->handle, E_MALLOC, __FILE__, __LINE__);
         return fooctx;
     }

     static void foo_freectx(void *fooctx)
     {
         free(fooctx);
     }

     static int foo_init(void *vfooctx)
     {
         struct foo_ctx_st *fooctx = vfooctx;

         fooctx->b = 0x33;
     }

     static int foo_update(void *vfooctx, unsigned char *in, size_t inl)
     {
         struct foo_ctx_st *fooctx = vfooctx;

         /* did you expect something serious? */
         if (inl == 0)
             return 1;
         for (; inl-- > 0; in++)
             *in ^= fooctx->b;
         return 1;
     }

     static int foo_final(void *vfooctx)
     {
         struct foo_ctx_st *fooctx = vfooctx;

         fooctx->b = 0x66;
     }

     static const OSSL_DISPATCH foo_fns[] = {
         { OSSL_FUNC_BAR_NEWCTX, (void (*)(void))foo_newctx },
         { OSSL_FUNC_BAR_FREECTX, (void (*)(void))foo_freectx },
         { OSSL_FUNC_BAR_INIT, (void (*)(void))foo_init },
         { OSSL_FUNC_BAR_UPDATE, (void (*)(void))foo_update },
         { OSSL_FUNC_BAR_FINAL, (void (*)(void))foo_final },
         OSSL_DISPATCH_END
     };

     static const OSSL_ALGORITHM bars[] = {
         { "FOO", "provider=chumbawamba", foo_fns },
         { NULL, NULL, NULL }
     };

     static const OSSL_ALGORITHM *p_query(void *provctx, int operation_id,
                                          int *no_store)
     {
         switch (operation_id) {
         case OSSL_OP_BAR:
             return bars;
         }
         return NULL;
     }

     static const OSSL_ITEM *p_reasons(void *provctx)
     {
         return reasons;
     }

     static void p_teardown(void *provctx)
     {
         free(provctx);
     }

     static const OSSL_DISPATCH prov_fns[] = {
         { OSSL_FUNC_PROVIDER_TEARDOWN, (void (*)(void))p_teardown },
         { OSSL_FUNC_PROVIDER_QUERY_OPERATION, (void (*)(void))p_query },
         { OSSL_FUNC_PROVIDER_GET_REASON_STRINGS, (void (*)(void))p_reasons },
         OSSL_DISPATCH_END
     };

     int OSSL_provider_init(const OSSL_CORE_HANDLE *handle,
                            const OSSL_DISPATCH *in,
                            const OSSL_DISPATCH **out,
                            void **provctx)
     {
         struct prov_ctx_st *pctx = NULL;

         for (; in->function_id != 0; in++)
             switch (in->function_id) {
             case OSSL_FUNC_CORE_PUT_ERROR:
                 c_put_error = OSSL_FUNC_core_put_error(in);
                 break;
             }

         *out = prov_fns;

         if ((pctx = malloc(sizeof(*pctx))) == NULL) {
             /*
              * ALEA IACTA EST, if the core retrieves the reason table
              * regardless, that string will be displayed, otherwise not.
              */
             c_put_error(handle, E_MALLOC, __FILE__, __LINE__);
             return 0;
         }
         pctx->handle = handle;
         return 1;
     }

    This relies on a few things existing in openssl/core_dispatch.h:

     #define OSSL_OP_BAR            4711

     #define OSSL_FUNC_BAR_NEWCTX      1
     typedef void *(OSSL_FUNC_bar_newctx_fn)(void *provctx);
     static ossl_inline OSSL_FUNC_bar_newctx(const OSSL_DISPATCH *opf)
     { return (OSSL_FUNC_bar_newctx_fn *)opf->function; }

     #define OSSL_FUNC_BAR_FREECTX     2
     typedef void (OSSL_FUNC_bar_freectx_fn)(void *ctx);
     static ossl_inline OSSL_FUNC_bar_freectx(const OSSL_DISPATCH *opf)
     { return (OSSL_FUNC_bar_freectx_fn *)opf->function; }

     #define OSSL_FUNC_BAR_INIT        3
     typedef void *(OSSL_FUNC_bar_init_fn)(void *ctx);
     static ossl_inline OSSL_FUNC_bar_init(const OSSL_DISPATCH *opf)
     { return (OSSL_FUNC_bar_init_fn *)opf->function; }

     #define OSSL_FUNC_BAR_UPDATE      4
     typedef void *(OSSL_FUNC_bar_update_fn)(void *ctx,
                                           unsigned char *in, size_t inl);
     static ossl_inline OSSL_FUNC_bar_update(const OSSL_DISPATCH *opf)
     { return (OSSL_FUNC_bar_update_fn *)opf->function; }

     #define OSSL_FUNC_BAR_FINAL       5
     typedef void *(OSSL_FUNC_bar_final_fn)(void *ctx);
     static ossl_inline OSSL_FUNC_bar_final(const OSSL_DISPATCH *opf)
     { return (OSSL_FUNC_bar_final_fn *)opf->function; }

SEE ALSO
    provider(7)

HISTORY
    The concept of providers and everything surrounding them was introduced
    in OpenSSL 3.0.

    Definitions for OSSL_CAPABILITY_TLS_SIGALG_MIN_DTLS and
    OSSL_CAPABILITY_TLS_SIGALG_MAX_DTLS were added in OpenSSL 3.5.

COPYRIGHT
    Copyright 2019-2025 The OpenSSL Project Authors. All Rights Reserved.

    Licensed under the Apache License 2.0 (the "License"). You may not use
    this file except in compliance with the License. You can obtain a copy
    in the file LICENSE in the source distribution or at
    <https://www.openssl.org/source/license.html>.

