openssl/doc/man7/provider-digest.pod

=pod

=head1 NAME

provider-digest - The digest library E<lt>-E<gt> provider functions

=head1 SYNOPSIS

=for comment multiple includes

 #include <openssl/core_numbers.h>
 #include <openssl/core_names.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.
  */

 /* 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 parameters */
 size_t OP_digest_size(void);
 size_t OP_digest_block_size(void);
 int OP_digest_set_params(void *dctx, const OSSL_PARAM params[]);
 int OP_digest_get_params(void *dctx, OSSL_PARAM params[]);

=head1 DESCRIPTION

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

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

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

All these "functions" have a corresponding function type definition
named B<OSSL_{name}_fn>, and a helper function to retrieve the
function pointer from an B<OSSL_DISPATCH> element named
B<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);

B<OSSL_DISPATCH> arrays are indexed by numbers that are provided as
macros in L<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_size          OSSL_FUNC_DIGEST_SIZE
 OP_digest_block_size    OSSL_FUNC_DIGEST_BLOCK_SIZE
 OP_digest_set_params    OSSL_FUNC_DIGEST_SET_PARAMS
 OP_digest_get_params    OSSL_FUNC_DIGEST_GET_PARAMS

A digest algorithm implementation may not implement all of these functions.
In order to be useable 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.

=head2 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 paramater B<provctx> is the provider context generated during provider
initialisation (see L<provider(3)>).

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

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

=head2 Digest Generation Functions

OP_digest_init() initialises a digest operation given a newly created
provider side digest context in the B<dctx> paramter.

OP_digest_update() is called to supply data to be digested as part of a
previously initialised digest operation.
The B<dctx> parameter contains a pointer to a previously initialised provider
side context.
OP_digest_update() should digest B<inl> bytes of data at the location pointed to
by B<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 B<dctx> parameter contains a pointer to the provider side context.
The digest should be written to B<*out> and the length of the digest to
B<*outl>.
The digest should not exceed B<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 B<provctx> parameter (see L<provider(3)>).
B<inl> bytes at B<in> should be digested and the result should be stored at
B<out>. The length of the digest should be stored in B<*outl> which should not
exceed B<outsz> bytes.

=head2 Digest Parameters

OP_digest_size() should return the size of the digest.

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

OP_digest_set_params() set digest parameters associated with the given provider
side digest context B<dctx> to B<params>.
Any parameter settings are additional to any that were previously set.
See L<OSSL_PARAM(3)> for further details on the parameters structure.

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

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

=over 4

=item B<OSSL_DIGEST_PARAM_XOFLEN> (size_t)

Sets the digest length for extendable output functions.

=item B<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.

=item B<OSSL_DIGEST_PARAM_PAD_TYPE> (int)

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.

=item B<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.

=back

=head1 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.

=head1 SEE ALSO

L<provider(7)>

=head1 HISTORY

The provider DIGEST interface was introduced in OpenSSL 3.0.

=head1 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
L<https://www.openssl.org/source/license.html>.

=cut