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=head1 NAME

EVP_PKEY_CTX_set_params,
EVP_PKEY_CTX_settable_params,
EVP_PKEY_CTX_get_params,
EVP_PKEY_CTX_gettable_params
- provider parameter passing operations

=head1 SYNOPSIS

 #include <openssl/evp.h>

 int EVP_PKEY_CTX_set_params(EVP_PKEY_CTX *ctx, const OSSL_PARAM *params);
 const OSSL_PARAM *EVP_PKEY_CTX_settable_params(const EVP_PKEY_CTX *ctx);
 int EVP_PKEY_CTX_get_params(EVP_PKEY_CTX *ctx, OSSL_PARAM *params);
 const OSSL_PARAM *EVP_PKEY_CTX_gettable_params(const EVP_PKEY_CTX *ctx);

=head1 DESCRIPTION

The EVP_PKEY_CTX_get_params() and EVP_PKEY_CTX_set_params() functions allow
transfer of arbitrary key parameters to and from providers.
Not all parameters may be supported by all providers.
See L<OSSL_PROVIDER(3)> for more information on providers.
See L<OSSL_PARAM(3)> for more information on parameters.
These functions must only be called after the EVP_PKEY_CTX has been initialised
for use in an operation.
These methods replace the EVP_PKEY_CTX_ctrl() mechanism. (EVP_PKEY_CTX_ctrl now
calls these methods internally to interact with providers).

EVP_PKEY_CTX_gettable_params() and EVP_PKEY_CTX_settable_params() get a
constant B<OSSL_PARAM> array that describes the gettable and
settable parameters for the current algorithm implementation, i.e. parameters
that can be used with EVP_PKEY_CTX_get_params() and EVP_PKEY_CTX_set_params()
respectively.
See L<OSSL_PARAM(3)> for the use of B<OSSL_PARAM> as parameter descriptor.
These functions must only be called after the EVP_PKEY_CTX has been initialised
for use in an operation.

=head2 Parameters

Examples of EVP_PKEY parameters include the following:

L<provider-keymgmt(7)/Common parameters>
L<provider-keyexch(7)/Key Exchange parameters>
L<provider-signature(7)/Signature parameters>

L<EVP_PKEY-RSA(7)/Common RSA parameters>
L<EVP_PKEY-RSA(7)/RSA key generation parameters>
L<EVP_PKEY-FFC(7)/FFC parameters>
L<EVP_PKEY-FFC(7)/FFC key generation parameters>
L<EVP_PKEY-DSA(7)/DSA parameters>
L<EVP_PKEY-DSA(7)/DSA key generation parameters>
L<EVP_PKEY-DH(7)/DH parameters>
L<EVP_PKEY-DH(7)/DH key generation parameters>
L<EVP_PKEY-EC(7)/Common EC parameters>
L<EVP_PKEY-X25519(7)/Common X25519, X448, ED25519 and ED448 parameters>

=head1 RETURN VALUES

EVP_PKEY_CTX_set_params() returns 1 for success or 0 otherwise.
EVP_PKEY_CTX_settable_params() returns an OSSL_PARAM array on success or NULL on
error.
It may also return NULL if there are no settable parameters available.

All other functions and macros described on this page return a positive value
for success and 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_encrypt(3)>,
L<EVP_PKEY_decrypt(3)>,
L<EVP_PKEY_sign(3)>,
L<EVP_PKEY_verify(3)>,
L<EVP_PKEY_verify_recover(3)>,
L<EVP_PKEY_derive(3)>,
L<EVP_PKEY_keygen(3)>

=head1 HISTORY

All functions were added in OpenSSL 3.0.

=head1 COPYRIGHT

Copyright 2020-2021 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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