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=head1 NAME

EVP_PKEY_copy_parameters, EVP_PKEY_missing_parameters, EVP_PKEY_cmp_parameters,
EVP_PKEY_cmp - public key parameter and comparison functions

=head1 SYNOPSIS

 #include <openssl/evp.h>

 int EVP_PKEY_missing_parameters(const EVP_PKEY *pkey);
 int EVP_PKEY_copy_parameters(EVP_PKEY *to, const EVP_PKEY *from);

 int EVP_PKEY_cmp_parameters(const EVP_PKEY *a, const EVP_PKEY *b);
 int EVP_PKEY_cmp(const EVP_PKEY *a, const EVP_PKEY *b);

=head1 DESCRIPTION

The function EVP_PKEY_missing_parameters() returns 1 if the public key
parameters of B<pkey> are missing and 0 if they are present or the algorithm
doesn't use parameters.

The function EVP_PKEY_copy_parameters() copies the parameters from key
B<from> to key B<to>. An error is returned if the parameters are missing in
B<from> or present in both B<from> and B<to> and mismatch. If the parameters
in B<from> and B<to> are both present and match this function has no effect.

The function EVP_PKEY_cmp_parameters() compares the parameters of keys
B<a> and B<b>.

The function EVP_PKEY_cmp() compares the public key components and parameters
(if present) of keys B<a> and B<b>.

=head1 NOTES

The main purpose of the functions EVP_PKEY_missing_parameters() and
EVP_PKEY_copy_parameters() is to handle public keys in certificates where the
parameters are sometimes omitted from a public key if they are inherited from
the CA that signed it.

Since OpenSSL private keys contain public key components too the function
EVP_PKEY_cmp() can also be used to determine if a private key matches
a public key.

=head1 RETURN VALUES

The function EVP_PKEY_missing_parameters() returns 1 if the public key
parameters of B<pkey> are missing and 0 if they are present or the algorithm
doesn't use parameters.

These functions EVP_PKEY_copy_parameters() returns 1 for success and 0 for
failure.

The function EVP_PKEY_cmp_parameters() and EVP_PKEY_cmp() return 1 if the
keys match, 0 if they don't match, -1 if the key types are different and
-2 if the operation is not supported.

=head1 SEE ALSO

L<EVP_PKEY_CTX_new(3)>,
L<EVP_PKEY_keygen(3)>

=head1 COPYRIGHT

Copyright 2006-2016 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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