Verify an Argon2 Password with a Secret and Memory Guard

Demonstrates Crypt2.Argon2VerifyPassword when the hash was created with a secret (pepper) or ad, and the use of maxMemoryKb to guard against untrusted hash strings.

<?php

include("chilkat.php");

$crypt = new CkCrypt2();

//  The password should come from a secure source rather than being hard-coded.
$password = 'correct horse battery staple';

$phcHash = '$argon2id$v=19$m=131072,t=4,p=2$c29tZXJhbmRvbXNhbHQ$3fJ7v1qKcVJ0lHqXjBQZ8mYm3sNTfSPRt0bqDl9kEyM';

//  When the hash was created with a secret (pepper) or ad, the same values must be supplied to verify.
//  Only the secret, ad, encoding, passwordCharset, and maxMemoryKb members of the options are used;
//  everything else is ignored.
$json = new CkJsonObject();
$json->UpdateString('secret','application-wide-pepper');
$json->UpdateString('secretEncoding','utf-8');

//  maxMemoryKb guards against a hash from an untrusted source claiming an enormous memory cost.  The
//  memory cost is taken from the hash string, so this limit is checked before any memory is allocated.
//  It defaults to 2 GB.
$json->UpdateInt('maxMemoryKb',262144);

//  Argon2VerifyPassword returns 1 if the password matched, 0 if it did not match, and -1 if the
//  verification could not be performed.  Always test for a match with == 1.
$verifyResult = $crypt->Argon2VerifyPassword($password,$json->emit(),$phcHash);
if ($verifyResult == 1) {
    print 'The password is verified.' . "\n";
}
else {
    if ($verifyResult == 0) {
        print 'The password does not match.' . "\n";
    }
    else {
        print 'The verification could not be performed: ' . $crypt->lastErrorText() . "\n";
    }

}


?>