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=head1 NAME

EVP_PKEY_supports_digest_nid - indicate support for signature digest

=head1 SYNOPSIS

 #include <openssl/evp.h>
 int EVP_PKEY_supports_digest_nid(EVP_PKEY *pkey, int nid);

=head1 DESCRIPTION

The EVP_PKEY_supports_digest_nid() function queries whether the message digest
NID B<nid> is supported for public key signature operations associated with key
B<pkey>.

=head1 NOTES

If the EVP_PKEY implementation does not explicitly support this method, but
L<EVP_PKEY_get_default_digest_nid(3)> returns a mandatory digest result, then
only that mandatory digest will be supported.

=head1 RETURN VALUES

The EVP_PKEY_supports_digest_nid() function returns 1 if the message digest
algorithm identified by B<nid> can be used for public key signature operations
associated with key B<pkey> and 0 if it cannot be used. It returns a negative
value for failure. In particular a return value of -2 indicates the query
operation is not supported by the public key algorithm.

=head1 SEE ALSO

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

=head1 HISTORY

This function was first added to OpenSSL 1.1.2.

=head1 COPYRIGHT

Copyright 2006-2018 The OpenSSL Project Authors. All Rights Reserved.

Licensed under the OpenSSL license (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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