=pod

=head1 NAME

EVP_PKEY_get_default_digest_nid, EVP_PKEY_get_default_digest_name
- get default signature digest

=head1 SYNOPSIS

 #include <openssl/evp.h>

 int EVP_PKEY_get_default_digest_name(EVP_PKEY *pkey,
                                      char *mdname, size_t mdname_sz);
 int EVP_PKEY_get_default_digest_nid(EVP_PKEY *pkey, int *pnid);

=head1 DESCRIPTION

EVP_PKEY_get_default_digest_name() fills in the default message digest
name for the public key signature operations associated with key
I<pkey> into I<mdname>, up to at most I<mdname_sz> bytes including the
ending NUL byte.  The name could be C<"UNDEF">, signifying that a digest
must (for return value 2) or may (for return value 1) be left unspecified.

EVP_PKEY_get_default_digest_nid() sets I<pnid> to the default message
digest NID for the public key signature operations associated with key
I<pkey>.  Note that some signature algorithms (i.e. Ed25519 and Ed448)
do not use a digest during signing.  In this case I<pnid> will be set
to NID_undef.  This function is only reliable for legacy keys, which
are keys with a B<EVP_PKEY_ASN1_METHOD>; these keys have typically
been loaded from engines, or created with L<EVP_PKEY_assign_RSA(3)> or
similar.

=head1 NOTES

For all current standard OpenSSL public key algorithms SHA256 is returned.

=head1 RETURN VALUES

EVP_PKEY_get_default_digest_name() and EVP_PKEY_get_default_digest_nid()
both return 1 if the message digest is advisory (that is other digests
can be used) and 2 if it is mandatory (other digests can not be used).
They return 0 or a negative value for failure.  In particular a return
value of -2 indicates the operation is not supported by the public key
algorithm.

=head1 SEE ALSO

L<EVP_PKEY_CTX_new(3)>,
L<EVP_PKEY_sign(3)>,
L<EVP_PKEY_digestsign_supports_digest(3)>,
L<EVP_PKEY_verify(3)>,
L<EVP_PKEY_verify_recover(3)>,

=head1 HISTORY

This function was added in OpenSSL 1.0.0.

=head1 COPYRIGHT

Copyright 2006-2023 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>.

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