Updated: 2022/Sep/29

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PROVIDER-DIGEST(7)                  OpenSSL                 PROVIDER-DIGEST(7)



NAME
       provider-digest - The digest library <-> provider functions

LIBRARY
       libcrypto, -lcrypto

SYNOPSIS
        #include <openssl/core_dispatch.h>
        #include <openssl/core_names.h>

        /*
         * Digests support the following function signatures in OSSL_DISPATCH arrays.
         * (The function signatures are not actual functions).
         */

        /* Context management */
        void *OSSL_FUNC_digest_newctx(void *provctx);
        void OSSL_FUNC_digest_freectx(void *dctx);
        void *OSSL_FUNC_digest_dupctx(void *dctx);

        /* Digest generation */
        int OSSL_FUNC_digest_init(void *dctx, const OSSL_PARAM params[]);
        int OSSL_FUNC_digest_update(void *dctx, const unsigned char *in, size_t inl);
        int OSSL_FUNC_digest_final(void *dctx, unsigned char *out, size_t *outl,
                                   size_t outsz);
        int OSSL_FUNC_digest_digest(void *provctx, const unsigned char *in, size_t inl,
                                    unsigned char *out, size_t *outl, size_t outsz);

        /* Digest parameter descriptors */
        const OSSL_PARAM *OSSL_FUNC_digest_gettable_params(void *provctx);

        /* Digest operation parameter descriptors */
        const OSSL_PARAM *OSSL_FUNC_digest_gettable_ctx_params(void *dctx,
                                                               void *provctx);
        const OSSL_PARAM *OSSL_FUNC_digest_settable_ctx_params(void *dctx,
                                                               void *provctx);

        /* Digest parameters */
        int OSSL_FUNC_digest_get_params(OSSL_PARAM params[]);

        /* Digest operation parameters */
        int OSSL_FUNC_digest_set_ctx_params(void *dctx, const OSSL_PARAM params[]);
        int OSSL_FUNC_digest_get_ctx_params(void *dctx, OSSL_PARAM params[]);

DESCRIPTION
       This documentation is primarily aimed at provider authors. See
       provider(7) for further information.

       The DIGEST operation enables providers to implement digest algorithms
       and make them available to applications via the API functions
       EVP_DigestInit_ex(3), EVP_DigestUpdate(3) and EVP_DigestFinal(3) (and
       other related functions).

       All "functions" mentioned here are passed as function pointers between
       libcrypto and the provider in OSSL_DISPATCH(3) arrays via
       OSSL_ALGORITHM(3) arrays that are returned by the provider's
       provider_query_operation() function (see "Provider Functions" in
       provider-base(7)).

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

        typedef void *(OSSL_FUNC_digest_newctx_fn)(void *provctx);
        static ossl_inline OSSL_FUNC_digest_newctx_fn
            OSSL_FUNC_digest_newctx(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:

        OSSL_FUNC_digest_newctx               OSSL_FUNC_DIGEST_NEWCTX
        OSSL_FUNC_digest_freectx              OSSL_FUNC_DIGEST_FREECTX
        OSSL_FUNC_digest_dupctx               OSSL_FUNC_DIGEST_DUPCTX

        OSSL_FUNC_digest_init                 OSSL_FUNC_DIGEST_INIT
        OSSL_FUNC_digest_update               OSSL_FUNC_DIGEST_UPDATE
        OSSL_FUNC_digest_final                OSSL_FUNC_DIGEST_FINAL
        OSSL_FUNC_digest_digest               OSSL_FUNC_DIGEST_DIGEST

        OSSL_FUNC_digest_get_params           OSSL_FUNC_DIGEST_GET_PARAMS
        OSSL_FUNC_digest_get_ctx_params       OSSL_FUNC_DIGEST_GET_CTX_PARAMS
        OSSL_FUNC_digest_set_ctx_params       OSSL_FUNC_DIGEST_SET_CTX_PARAMS

        OSSL_FUNC_digest_gettable_params      OSSL_FUNC_DIGEST_GETTABLE_PARAMS
        OSSL_FUNC_digest_gettable_ctx_params  OSSL_FUNC_DIGEST_GETTABLE_CTX_PARAMS
        OSSL_FUNC_digest_settable_ctx_params  OSSL_FUNC_DIGEST_SETTABLE_CTX_PARAMS

       A digest algorithm implementation may not implement all of these
       functions.  In order to be usable all or none of
       OSSL_FUNC_digest_newctx, OSSL_FUNC_digest_freectx,
       OSSL_FUNC_digest_init, OSSL_FUNC_digest_update and
       OSSL_FUNC_digest_final should be implemented.  All other functions are
       optional.

   Context Management Functions
       OSSL_FUNC_digest_newctx() should create and return a pointer to a
       provider side structure for holding context information during a digest
       operation.  A pointer to this context will be passed back in a number
       of the other digest operation function calls.  The parameter provctx is
       the provider context generated during provider initialisation (see
       provider(7)).

       OSSL_FUNC_digest_freectx() is passed a pointer to the provider side
       digest context in the dctx parameter.  This function should free any
       resources associated with that context.

       OSSL_FUNC_digest_dupctx() should duplicate the provider side digest
       context in the dctx parameter and return the duplicate copy.

   Digest Generation Functions
       OSSL_FUNC_digest_init() initialises a digest operation given a newly
       created provider side digest context in the dctx parameter.  The
       params, if not NULL, should be set on the context in a manner similar
       to using OSSL_FUNC_digest_set_ctx_params().

       OSSL_FUNC_digest_update() is called to supply data to be digested as
       part of a previously initialised digest operation.  The dctx parameter
       contains a pointer to a previously initialised provider side context.
       OSSL_FUNC_digest_update() should digest inl bytes of data at the
       location pointed to by in.  OSSL_FUNC_digest_update() may be called
       multiple times for a single digest operation.

       OSSL_FUNC_digest_final() generates a digest started through previous
       OSSL_FUNC_digest_init() and OSSL_FUNC_digest_update() calls.  The dctx
       parameter contains a pointer to the provider side context.  The digest
       should be written to *out and the length of the digest to *outl.  The
       digest should not exceed outsz bytes.

       OSSL_FUNC_digest_digest() is a "oneshot" digest function.  No provider
       side digest context is used.  Instead the provider context that was
       created during provider initialisation is passed in the provctx
       parameter (see provider(7)).  inl bytes at in should be digested and
       the result should be stored at out. The length of the digest should be
       stored in *outl which should not exceed outsz bytes.

   Digest Parameters
       See OSSL_PARAM(3) for further details on the parameters structure used
       by these functions.

       OSSL_FUNC_digest_get_params() gets details of the algorithm
       implementation and stores them in params.

       OSSL_FUNC_digest_set_ctx_params() sets digest operation parameters for
       the provider side digest context dctx to params.  Any parameter
       settings are additional to any that were previously set.  Passing NULL
       for params should return true.

       OSSL_FUNC_digest_get_ctx_params() gets digest operation details details
       from the given provider side digest context dctx and stores them in
       params.  Passing NULL for params should return true.

       OSSL_FUNC_digest_gettable_params() returns a constant OSSL_PARAM(3)
       array containing descriptors of the parameters that
       OSSL_FUNC_digest_get_params() can handle.

       OSSL_FUNC_digest_gettable_ctx_params() and
       OSSL_FUNC_digest_settable_ctx_params() both return constant
       OSSL_PARAM(3) arrays as descriptors of the parameters that
       OSSL_FUNC_digest_get_ctx_params() and OSSL_FUNC_digest_set_ctx_params()
       can handle, respectively.  The array is based on the current state of
       the provider side context if dctx is not NULL and on the provider side
       algorithm provctx otherwise.

       Parameters currently recognised by built-in digests with this function
       are as follows. Not all parameters are relevant to, or are understood
       by all digests:

       "blocksize" (OSSL_DIGEST_PARAM_BLOCK_SIZE) <unsigned integer>
           The digest block size.  The length of the "blocksize" parameter
           should not exceed that of a size_t.

       "size" (OSSL_DIGEST_PARAM_SIZE) <unsigned integer>
           The digest output size.  The length of the "size" parameter should
           not exceed that of a size_t.

       "flags" (OSSL_DIGEST_PARAM_FLAGS) <unsigned integer>
           Diverse flags that describe exceptional behaviour for the digest:

           EVP_MD_FLAG_ONESHOT
               This digest method can only handle one block of input.

           EVP_MD_FLAG_XOF
               This digest method is an extensible-output function (XOF) and
               supports setting the OSSL_DIGEST_PARAM_XOFLEN parameter.

           EVP_MD_FLAG_DIGALGID_NULL
               When setting up a DigestAlgorithmIdentifier, this flag will
               have the parameter set to NULL by default.  Use this for
               PKCS#1.  Note: if combined with EVP_MD_FLAG_DIGALGID_ABSENT,
               the latter will override.

           EVP_MD_FLAG_DIGALGID_ABSENT
               When setting up a DigestAlgorithmIdentifier, this flag will
               have the parameter be left absent by default.  Note: if
               combined with EVP_MD_FLAG_DIGALGID_NULL, the latter will be
               overridden.

           EVP_MD_FLAG_DIGALGID_CUSTOM
               Custom DigestAlgorithmIdentifier handling via ctrl, with
               EVP_MD_FLAG_DIGALGID_ABSENT as default.  Note: if combined with
               EVP_MD_FLAG_DIGALGID_NULL, the latter will be overridden.
               Currently unused.

           The length of the "flags" parameter should equal that of an
           unsigned long int.

   Digest Context Parameters
       OSSL_FUNC_digest_set_ctx_params() sets digest parameters associated
       with the given provider side digest context dctx to params.  Any
       parameter settings are additional to any that were previously set.  See
       OSSL_PARAM(3) for further details on the parameters structure.

       OSSL_FUNC_digest_get_ctx_params() gets details of currently set
       parameters values associated with the give provider side digest context
       dctx and stores them in params.  See OSSL_PARAM(3) for further details
       on the parameters structure.

RETURN VALUES
       OSSL_FUNC_digest_newctx() and OSSL_FUNC_digest_dupctx() should return
       the newly created provider side digest context, or NULL on failure.

       OSSL_FUNC_digest_init(), OSSL_FUNC_digest_update(),
       OSSL_FUNC_digest_final(), OSSL_FUNC_digest_digest(),
       OSSL_FUNC_digest_set_params() and OSSL_FUNC_digest_get_params() should
       return 1 for success or 0 on error.

       OSSL_FUNC_digest_size() should return the digest size.

       OSSL_FUNC_digest_block_size() should return the block size of the
       underlying digest algorithm.

BUGS
       The EVP_Q_digest(), EVP_Digest() and EVP_DigestFinal_ex() API calls do
       not expect the digest size to be larger than EVP_MAX_MD_SIZE. Any
       algorithm which produces larger digests is unusable with those API
       calls.

SEE ALSO
       provider(7), OSSL_PROVIDER-FIPS(7), OSSL_PROVIDER-default(7),
       OSSL_PROVIDER-legacy(7), EVP_MD-common(7), EVP_MD-BLAKE2(7),
       EVP_MD-MD2(7), EVP_MD-MD4(7), EVP_MD-MD5(7), EVP_MD-MD5-SHA1(7),
       EVP_MD-MDC2(7), EVP_MD-RIPEMD160(7), EVP_MD-SHA1(7), EVP_MD-SHA2(7),
       EVP_MD-SHA3(7), EVP_MD-SHAKE(7), EVP_MD-SM3(7), EVP_MD-WHIRLPOOL(7),
       EVP_MD-NULL(7), life_cycle-digest(7), EVP_DigestInit(3)

HISTORY
       The provider DIGEST interface was introduced in OpenSSL 3.0.

COPYRIGHT
       Copyright 2019-2023 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>.



3.0.12                            2023-05-31                PROVIDER-DIGEST(7)