Document EVP_MD constructors, destructors and manipulators

=pod

=head1 NAME

EVP_MD_meth_new, EVP_MD_meth_free, EVP_MD_meth_set_input_blocksize,

EVP_MD_meth_set_result_size, EVP_MD_meth_set_app_datasize,

EVP_MD_meth_set_flags, EVP_MD_meth_set_init, EVP_MD_meth_set_update,

EVP_MD_meth_set_final, EVP_MD_meth_set_copy, EVP_MD_meth_set_cleanup,

EVP_MD_meth_set_ctrl, EVP_MD_meth_get_input_blocksize,

EVP_MD_meth_get_result_size, EVP_MD_meth_get_app_datasize,

EVP_MD_meth_get_flags, EVP_MD_meth_get_init, EVP_MD_meth_get_update,

EVP_MD_meth_get_final, EVP_MD_meth_get_copy, EVP_MD_meth_get_cleanup,

EVP_MD_meth_get_ctrl, EVP_MD_meth_get_pkey_types,

EVP_MD_meth_get_sign, EVP_MD_meth_get_verify - Routines to build up

EVP_MD methods

=head1 SYNOPSIS

 #include <openssl/evp.h>

 EVP_MD *EVP_MD_create_method(int md_type, int pkey_type);

 EVP_MD *EVP_MD_meth_dup(const EVP_MD *md);

 void EVP_MD_destroy_method(EVP_MD *md);

 int EVP_MD_meth_set_input_blocksize(EVP_MD *md, int blocksize);

 int EVP_MD_meth_set_result_size(EVP_MD *md, int resultsize);

 int EVP_MD_meth_set_app_datasize(EVP_MD *md, int datasize);

 int EVP_MD_meth_set_flags(EVP_MD *md, unsigned long flags);

 int EVP_MD_meth_set_init(EVP_MD *md, int (*init)(EVP_MD_CTX *ctx));

 int EVP_MD_meth_set_update(EVP_MD *md, int (*update)(EVP_MD_CTX *ctx,

                                                      const void *data,

                                                      size_t count));

 int EVP_MD_meth_set_final(EVP_MD *md, int (*final)(EVP_MD_CTX *ctx,

                                                    unsigned char *md));

 int EVP_MD_meth_set_copy(EVP_MD *md, int (*copy)(EVP_MD_CTX *to,

                                                  const EVP_MD_CTX *from));

 int EVP_MD_meth_set_cleanup(EVP_MD *md, int (*cleanup)(EVP_MD_CTX *ctx));

 int EVP_MD_meth_set_ctrl(EVP_MD *md, int (*ctrl)(EVP_MD_CTX *ctx, int cmd,

                                                  int p1, void *p2));

 int EVP_MD_meth_get_input_blocksize(const EVP_MD *md);

 int EVP_MD_meth_get_result_size(const EVP_MD *md);

 int EVP_MD_meth_get_app_datasize(const EVP_MD *md);

 unsigned long EVP_MD_meth_get_flags(const EVP_MD *md);

 int (*EVP_MD_meth_get_init(const EVP_MD *md))(EVP_MD_CTX *ctx);

 int (*EVP_MD_meth_get_update(const EVP_MD *md))(EVP_MD_CTX *ctx,

                                                 const void *data,

                                                 size_t count);

 int (*EVP_MD_meth_get_final(const EVP_MD *md))(EVP_MD_CTX *ctx,

                                                unsigned char *md);

 int (*EVP_MD_meth_get_copy(const EVP_MD *md))(EVP_MD_CTX *to,

                                               const EVP_MD_CTX *from);

 int (*EVP_MD_meth_get_cleanup(const EVP_MD *md))(EVP_MD_CTX *ctx);

 int (*EVP_MD_meth_get_ctrl(const EVP_MD *md))(EVP_MD_CTX *ctx, int cmd,

                                               int p1, void *p2);

=head1 DESCRIPTION

The B<EVP_MD> type is a structure for digest method implementation.

It can also have associated public/private key signing and verifying

routines.

EVP_MD_meth_new() creates a new B<EVP_MD> structure.

EVP_MD_meth_dup() creates a copy of B<md>.

EVP_MD_meth_free() destroys a B<EVP_MD> structure.

EVP_MD_meth_set_input_blocksize() sets the internal input block size

for the method B<md> to B<blocksize> bytes.

EVP_MD_meth_set_result_size() sets the size of the result that the

digest method in B<md> is expected to produce to B<resultsize> bytes.

The digest method may have its own private data, which OpenSSL will

allocate for it.  EVP_MD_meth_set_app_datasize() should be used to

set the size for it to B<datasize>.

EVP_MD_meth_set_flags() sets the flags to describe optional

behaviours in the particular B<md>.  Several flags can be or'd

together.  The available flags are:

=over 4

=item EVP_MD_FLAG_ONESHOT

This digest method can only handles one block of input.

=item 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.  I<Note: if

combined with EVP_MD_FLAG_DIGALGID_ABSENT, the latter will override.>

=item EVP_MD_FLAG_DIGALGID_ABSENT

When setting up a DigestAlgorithmIdentifier, this flag will have the

parameter be left absent by default.  I<Note: if combined with

EVP_MD_FLAG_DIGALGID_NULL, the latter will be overriden.>

=item EVP_MD_FLAG_DIGALGID_CUSTOM

Custom DigestAlgorithmIdentifier handling via ctrl, with

B<EVP_MD_FLAG_DIGALGID_ABSENT> as default.  I<Note: if combined with

EVP_MD_FLAG_DIGALGID_NULL, the latter will be overriden.>

Currently unused.

=back

EVP_MD_meth_set_init() sets the digest init function for B<md>.

The digest init function is called by EVP_DigestInit(),

EVP_DigestInit_ex(), EVP_SignInit, EVP_SignInit_ex(), EVP_VerifyInit()

and EVP_VerifyInit_ex().

EVP_MD_meth_set_update() sets the digest update function for B<md>.

The digest update function is called by EVP_DigestUpdate(),

EVP_SignUpdate().

EVP_MD_meth_set_final() sets the digest final function for B<md>.

The digest final function is called by EVP_DigestFinal(),

EVP_DigestFinal_ex(), EVP_SignFinal() and EVP_VerifyFinal().

EVP_MD_meth_set_copy() sets the function for B<md> to do extra

computations after the method's private data structure has been copied

from one B<EVP_MD_CTX> to another.  If all that's needed is to copy

the data, there is no need for this copy function.

Note that the copy function is passed two B<EVP_MD_CTX *>, the private

data structure is then available with EVP_MD_CTX_md_data().

This copy function is called by EVP_MD_CTX_copy() and

EVP_MD_CTX_copy_ex().

EVP_MD_meth_set_cleanup() sets the function for B<md> to do extra

cleanup before the method's privata data structure is cleaned out and

freed.

Note that the cleanup function is passed a B<EVP_MD_CTX *>, the

private data structure is then available with EVP_MD_CTX_md_data().

This cleanup function is called by EVP_MD_CTX_reset() and

EVP_MD_CTX_free().

EVP_MD_meth_set_ctrl() sets the control function for B<md>.

EVP_MD_meth_get_input_blocksize(), EVP_MD_meth_get_result_size(),

EVP_MD_meth_get_app_datasize(), EVP_MD_meth_get_flags(),

EVP_MD_meth_get_init(), EVP_MD_meth_get_update(),

EVP_MD_meth_get_final(), EVP_MD_meth_get_copy(),

EVP_MD_meth_get_cleanup() and EVP_MD_meth_get_ctrl() are all used

to retrieve the method data given with the EVP_MD_meth_set_*()

functions above.

=head1 SEE ALSO

L<EVP_DigestInit(3)>, L<EVP_SignInit(3)>, L<EVP_VerifyInit(3)>

=head1 HISTORY

The B<EVP_MD> structure was openly available in OpenSSL before version

1.1.  The functions described here were added in OpenSSL version 1.1.

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