PROVIDER-DIGEST(7SSL) OpenSSL PROVIDER-DIGEST(7SSL)
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>.
3.5.4 2025-09-30 PROVIDER-DIGEST(7SSL)
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