Document EVP_MD constructors, destructors and manipulators

Reviewed-by: NRich Salz <rsalz@openssl.org>

doc/crypto/EVP_MD_meth_new.pod

+=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.
+
+=cut