Is openssl_free_key required?

Question

I'm working on some legacy code and encountered openssl key encryption that throws E_WARNING with error message "openssl_free_key() expects parameter 1 to be resource, string given".

Upon closer inspection, I found out that private key is indeed a string instead resource.

Since key is a string and key was not generated by "openssl_get_privatekey", is "openssl_free_key" required at the end of request?

Searching and looking at PHP docs, gives no definitive information regarding this problem.

$value = 'something';

if (openssl_pkcs12_read($file, $cart, $pass) === true) {
    $private_key = $cart['pkey'];
} else {
    throw new Exception('Failed to open certificate.');
}

if (isset($private_key)) {
    openssl_sign($value, $signature, $private_key, OPENSSL_ALGO_SHA1);
    openssl_free_key($private_key);
}

Answer 1

The docs say:

This function frees a private key created by openssl_pkey_new().

PHP Docs

So if your key is a string: no.