EVP_PKEY_gettable_params, EVP_PKEY_get_params, EVP_PKEY_get_int_param, EVP_PKEY_get_size_t_param,

       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
       <https://www.openssl.org/source/license.html>.

3.5.0                                              2025-06-04                     EVP_PKEY_GETTABLE_PARAMS(3SSL)

       See OSSL_PARAM(3) for information about parameters.

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

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

       An OSSL_PARAM(3) of type OSSL_PARAM_INTEGER or 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 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 size_t type using
       EVP_PKEY_get_size_t_param() will also fail.

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

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

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

       EVP_PKEY_get_utf8_string_param() get a key pkey UTF8 string value into a buffer str of maximum size
       max_buf_sz associated with a name of key_name.  The maximum size must be large enough to accommodate the
       string value including a terminating NUL byte, or this function will fail.  If out_len is not NULL,
       *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 *out_len by calling the function with
       str set to NULL.

       EVP_PKEY_get_octet_string_param() get a key pkey's octet string value into a buffer buf of maximum size
       max_buf_sz associated with a name of key_name.  If out_len is not NULL, *out_len is set to the length of
       the contents.  The required buffer size can be obtained from *out_len by calling the function with buf
       set to NULL.

        #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);

       These functions were added in OpenSSL 3.0.

       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

       These functions only work for EVP_PKEYs that contain a provider side key.

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 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 max_buf_sz is not big enough to hold the value.  If out_len is not
       NULL, *out_len will be assigned the required buffer size to hold the value.

EVP_PKEY_CTX_new(3), provider-keymgmt(7), OSSL_PARAM(3)

        #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);