=pod

=head1 NAME

EVP_PKEY_gettable_params, EVP_PKEY_get_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_params(const EVP_PKEY *pkey, OSSL_PARAM params[]);
 int EVP_PKEY_get_int_param(const EVP_PKEY *pkey, const char *key_name,
                            int *out);
 int EVP_PKEY_get_size_t_param(const EVP_PKEY *pkey, const char *key_name,
                               size_t *out);
 int EVP_PKEY_get_bn_param(const EVP_PKEY *pkey, const char *key_name,
                           BIGNUM **bn);
 int EVP_PKEY_get_utf8_string_param(const EVP_PKEY *pkey, const char *key_name,
                                    char *str, size_t max_buf_sz,
                                    size_t *out_len);
 int EVP_PKEY_get_octet_string_param(const EVP_PKEY *pkey, const char *key_name,
                                     unsigned char *buf, size_t max_buf_sz,
                                     size_t *out_len);

=head1 DESCRIPTION

See L<OSSL_PARAM(3)> for information about parameters.

EVP_PKEY_get_params() retrieves parameters from the key I<pkey>, according to
the contents of I<params>.

EVP_PKEY_gettable_params() returns a constant list of I<params> indicating
the names and types of key parameters that can be retrieved.

An L<OSSL_PARAM(3)> of type B<OSSL_PARAM_INTEGER> or
B<OSSL_PARAM_UNSIGNED_INTEGER> is of arbitrary length. Such a parameter can be
obtained using any of the functions EVP_PKEY_get_int_param(),
EVP_PKEY_get_size_t_param() or EVP_PKEY_get_bn_param(). Attempting to
obtain an integer value that does not fit into a native C B<int> type will cause
EVP_PKEY_get_int_param() to fail. Similarly attempting to obtain an integer
value that is negative or does not fit into a native C B<size_t> type using
EVP_PKEY_get_size_t_param() will also fail.

EVP_PKEY_get_int_param() retrieves a key I<pkey> integer value I<*out>
associated with a name of I<key_name> if it fits into C<int> type. For
parameters that do not fit into C<int> use EVP_PKEY_get_bn_param().

EVP_PKEY_get_size_t_param() retrieves a key I<pkey> size_t value I<*out>
associated with a name of I<key_name> if it fits into C<size_t> type. For
parameters that do not fit into C<size_t> use EVP_PKEY_get_bn_param().

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 into a
buffer I<str> of maximum size I<max_buf_sz> associated with a name of
I<key_name>.  The maximum size must be large enough to accomodate the string
value including a terminating NUL byte, or this function will fail.
If I<out_len> is not NULL, I<*out_len> is set to the length of the string
not including the terminating NUL byte. The required buffer size not including
the terminating NUL byte can be obtained from I<*out_len> by calling the
function with I<str> set to NULL.

EVP_PKEY_get_octet_string_param() get a key 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>.
If I<out_len> is not NULL, I<*out_len> is set to the length of the contents.
The required buffer size can be obtained from I<*out_len> by calling the
function with I<buf> set to 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.  If I<out_len> is not NULL, I<*out_len> will be assigned the required
buffer size 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_GROUP_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 2020-2022 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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