PROVIDER-DIGEST(7)

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

SYNOPSIS
 #include <openssl/core_numbers.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 *OP_digest_newctx(void *provctx);
 void OP_digest_freectx(void *dctx);
 void *OP_digest_dupctx(void *dctx);

 /* Digest generation */
 int OP_digest_init(void *dctx);
 int OP_digest_update(void *dctx, const unsigned char *in, size_t inl);
 int OP_digest_final(void *dctx, unsigned char *out, size_t *outl,
                     size_t outsz);
 int OP_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 *OP_digest_gettable_params(void);

 /* Digest operation parameter descriptors */
 const OSSL_PARAM *OP_digest_gettable_ctx_params(void);
 const OSSL_PARAM *OP_digest_settable_ctx_params(void);

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

 /* Digest operation parameters */
 int OP_digest_set_ctx_params(void *dctx, const OSSL_PARAM params[]);
 int OP_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 arrays via OSSL_ALGORITHM 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_{name}_fn, and a helper function to retrieve the function pointer from an OSSL_DISPATCH element named OSSL_get_{name}. For example, the "function" OP_digest_newctx() has these:

 typedef void *(OSSL_OP_digest_newctx_fn)(void *provctx);
 static ossl_inline OSSL_OP_digest_newctx_fn
     OSSL_get_OP_digest_newctx(const OSSL_DISPATCH *opf);

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

 OP_digest_newctx               OSSL_FUNC_DIGEST_NEWCTX
 OP_digest_freectx              OSSL_FUNC_DIGEST_FREECTX
 OP_digest_dupctx               OSSL_FUNC_DIGEST_DUPCTX

 OP_digest_init                 OSSL_FUNC_DIGEST_INIT
 OP_digest_update               OSSL_FUNC_DIGEST_UPDATE
 OP_digest_final                OSSL_FUNC_DIGEST_FINAL
 OP_digest_digest               OSSL_FUNC_DIGEST_DIGEST

 OP_digest_get_params           OSSL_FUNC_DIGEST_GET_PARAMS
 OP_digest_get_ctx_params       OSSL_FUNC_DIGEST_GET_CTX_PARAMS
 OP_digest_set_ctx_params       OSSL_FUNC_DIGEST_SET_CTX_PARAMS

 OP_digest_gettable_params      OSSL_FUNC_DIGEST_GETTABLE_PARAMS
 OP_digest_gettable_ctx_params  OSSL_FUNC_DIGEST_GETTABLE_CTX_PARAMS
 OP_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 OP_digest_newctx, OP_digest_freectx, OP_digest_init, OP_digest_update and OP_digest_final should be implemented. All other functions are optional.

  Context Management Functions
OP_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)).

OP_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.

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

  Digest Generation Functions
OP_digest_init() initialises a digest operation given a newly created provider side digest context in the dctx parameter.

OP_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. OP_digest_update() should digest inl bytes of data at the location pointed to by in. OP_digest_update() may be called multiple times for a single digest operation.

OP_digest_final() generates a digest started through previous OP_digest_init() and OP_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.

OP_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.

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

OP_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.

OP_digest_get_ctx_params() gets digest operation details details from the given provider side digest context dctx and stores them in params.

OP_digest_gettable_params(), OP_digest_gettable_ctx_params(), and OP_digest_settable_ctx_params() all return constant OSSL_PARAM arrays as descriptors of the parameters that OP_digest_get_params(), OP_digest_get_ctx_params(), and OP_digest_set_ctx_params() can handle, respectively.

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
OP_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.

OP_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.

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

"xoflen" (OSSL_DIGEST_PARAM_XOFLEN) <unsigned integer>
    Sets the digest length for extendable output functions. The length of the "xoflen" parameter should not exceed that of a size_t.

"ssl3-ms" (OSSL_DIGEST_PARAM_SSL3_MS) <octet string>
    This parameter is set by libssl in order to calculate a signature hash for an SSLv3 CertificateVerify message as per RFC6101. It is only set after all handshake messages have already been digested via OP_digest_update() calls. The parameter provides the master secret value to be added to the digest. The digest implementation should calculate the complete digest as per RFC6101 section 5.6.8. The next call after setting this parameter will be OP_digest_final(). This is only relevant for implementations of SHA1 or MD5_SHA1.

"pad_type" (OSSL_DIGEST_PARAM_PAD_TYPE) <unsigned integer>
    Sets the pad type to be used. The only built-in digest that uses this is MDC2. Normally the final MDC2 block is padded with 0s. If the pad type is set to 2 then the final block is padded with 0x80 followed by 0s.

"micalg" (OSSL_DIGEST_PARAM_MICALG) <UTF8 string>
    Gets the digest Message Integrity Check algorithm string. This is used when creating S/MIME multipart/signed messages, as specified in RFC 5751.

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

OP_digest_init(), OP_digest_update(), OP_digest_final(), OP_digest_digest(), OP_digest_set_params() and OP_digest_get_params() should return 1 for success or 0 on error.

OP_digest_size() should return the digest size.

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

SEE ALSO
provider(7)

HISTORY
The provider DIGEST interface was introduced in OpenSSL 3.0.

COPYRIGHT
Copyright 2019 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>.