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

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);
     void OSSL_FUNC_digest_copyctx(void *voutctx, void *vinctx);

     /* 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_copyctx              OSSL_FUNC_DIGEST_COPYCTX

     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, OSSL_FUNC_digest_final and
    OSSL_FUNC_digest_get_params 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.

    OSSL_FUNC_digest_copyctx() should copy the provider side digest context
    in the *vinctx* parameter to the *voutctx* parameter which is the
    another provider side context. The OSSL_FUNC_digest_copyctx function is
    used in the EVP_MD_CTX_copy_ex function to speed up HMAC operations in
    the PBKDF2. This function is optional, and dupctx will be used if there
    is no EVP_MD_CTX_copy_ex function.

  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).

        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-KECCAK(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.
    OSSL_FUNC_digest_copyctx() was added in 3.5 version.

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>.

