X509_check_private_key.3ssl - Man Page

 #include <openssl/x509.h>

 int X509_check_private_key(X509 *x, EVP_PKEY *k);

 int X509_REQ_check_private_key(X509_REQ *x, EVP_PKEY *k);

X509_check_private_key() function checks the consistency of private key k with the public key in x.

X509_REQ_check_private_key() is equivalent to X509_check_private_key() except that x represents a certificate request of structure X509_REQ.

X509_check_private_key() and X509_REQ_check_private_key() return 1 if the keys match each other, and 0 if not.

If the key is invalid or an error occurred, the reason code can be obtained using ERR_get_error(3).

The check_private_key functions don't check if k itself is indeed a private key or not. It merely compares the public materials (e.g. exponent and modulus of an RSA key) and/or key parameters (e.g. EC params of an EC key) of a key pair. So if you pass a public key to these functions in k, it will return success.

ERR_get_error(3)

Copyright 2017-2018 The OpenSSL Project Authors. All Rights Reserved.

Licensed under the OpenSSL license (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>.

The man page X509_REQ_check_private_key.3ssl(3) is an alias of X509_check_private_key.3ssl(3).