PHP openssl_spki_export_challenge() Function

The openssl_spki_export_challenge() function is an inbuilt function in PHP and is used to export the signed public key and the challenge associated with it. It verifies a signed public key and challenge.

Syntax:

string openssl_spki_export_challenge( string &$spkac )

Parameters: This function accepts single parameter as mentioned above and described below:

• $spkac: This parameter is a format for sending a Certification Signing Request which encodes a public key that can be manipulated using openssl.

Return Values: This function returns the associated challenge string or NULL on failure.

Errors/Exceptions: If an invalid argument is passed using the "spkac" parameter, the E_WARNING level emits an error.

<?php

$pkey   = openssl_pkey_new(array("spki"));
$inputChallengeString = "geeks";

// Generate a new key pair using 
// "geeksforgeeks" as challenge string
$spkac = openssl_spki_new(
        $pkey, $inputChallengeString);
 
// Extract challenge key from key
$extractedChallengeString = 
    openssl_spki_export_challenge(
    preg_replace('/SPKAC=/', '', $spkac));
 
//if challenge string is not null
if (! is_null($extractedChallengeString)) {
    echo "Used challenge string is:" 
        . $inputChallengeString."\n";
        
    // print challenge key
    echo "Extracted challenge string is:"
        . $extractedChallengeString . "\n";
}

?>

Output:

Used challenge string is:geeks
Extracted challenge string is:geeks