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=head1 NAME

EVP_PKEY_gettable_params, EVP_PKEY_get_int_param, EVP_PKEY_get_size_t_param,
EVP_PKEY_get_bn_param, EVP_PKEY_get_utf8_string_param,
EVP_PKEY_get_octet_string_param
- retrieve key parameters from a key

=head1 SYNOPSIS

 #include <openssl/evp.h>

 const OSSL_PARAM *EVP_PKEY_gettable_params(EVP_PKEY *pkey);
 int EVP_PKEY_get_int_param(EVP_PKEY *pkey, const char *key_name, int *out);
 int EVP_PKEY_get_size_t_param(EVP_PKEY *pkey, const char *key_name, size_t *out);
 int EVP_PKEY_get_bn_param(EVP_PKEY *pkey, const char *key_name, BIGNUM **bn);
 int EVP_PKEY_get_utf8_string_param(EVP_PKEY *pkey, const char *key_name,
                                    char *str, size_t max_buf_sz, size_t *out_sz);
 int EVP_PKEY_get_octet_string_param(EVP_PKEY *pkey, const char *key_name,
                                    unsigned char *buf, size_t max_buf_sz,
                                    size_t *out_sz);

=head1 DESCRIPTION

EVP_PKEY_gettable_params() returns a constant list of I<params> indicating
the names and types of key parameters that can be retrieved.
See L<OSSL_PARAM(3)> for information about parameters.

EVP_PKEY_get_int_param() retrieves a key I<pkey> integer value I<*out>
associated with a name of I<key_name>.

EVP_PKEY_get_size_t_param() retrieves a key I<pkey> size_t value I<*out>
associated with a name of I<key_name>.

EVP_PKEY_get_bn_param() retrieves a key I<pkey> BIGNUM value I<**bn>
associated with a name of I<key_name>. If I<*bn> is NULL then the BIGNUM
is allocated by the method.

EVP_PKEY_get_utf8_string_param() get a key I<pkey> UTF8 string value int a buffer
I<str> of maximum size I<max_buf_sz> associated with a name of I<key_name>.
I<*out_sz> is the returned size of the string if it is not NULL.

EVP_PKEY_get_octet_string_param() copy a I<pkey>'s octet string value into a buffer
I<buf> of maximum size I<max_buf_sz> associated with a name of I<key_name>.
I<*out_sz> is the returned size of the buffer if it is not NULL.

=head1 NOTES

These functions only work for B<EVP_PKEY>s that contain a provider side key.

=head1 RETURN VALUES

EVP_PKEY_gettable_params() returns NULL on error or if it is not supported,

All other methods return 1 if a value associated with the key's I<key_name> was
successfully returned, or 0 if there was an error.
An error may be returned by methods EVP_PKEY_get_utf8_string_param() and
EVP_PKEY_get_octet_string_param() if I<max_buf_sz> is not big enough to hold the
value.

=head1 EXAMPLES

 #include <openssl/evp.h>

 char *curve_name[64];
 unsigned char pub[256];
 BIGNUM *bn_priv = NULL;

 /*
  * NB: assumes 'key' is set up before the next step. In this example the key
  * is an EC key.
  */

 if (!EVP_PKEY_get_utf8_string_param(key, OSSL_PKEY_PARAM_EC_NAME,
                                     curve_name, sizeof(curve_name), &len)) {
   /* Error */
 }
 if (!EVP_PKEY_get_octet_string_param(key, OSSL_PKEY_PARAM_PUB_KEY,
                                      pub, sizeof(pub), &len)) {
     /* Error */
 }
 if (!EVP_PKEY_get_bn_param(key, OSSL_PKEY_PARAM_PRIV_KEY, &bn_priv)) {
     /* Error */
 }


 BN_clear_free(bn_priv);

=head1 SEE ALSO

L<EVP_PKEY_CTX_new(3)>, L<provider-keymgmt(7)>, L<OSSL_PARAM(3)>

=head1 HISTORY

These functions were added in OpenSSL 3.0.

=head1 COPYRIGHT

Copyright 2020 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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