function simpleCheckMessageSignature($password, $body, $signature)
{
    if (!WITH_SIGNATURE) {
        return true;
    }
    $computedSignature = simpleSignMessage($password, $body);
    return $computedSignature == $signature;
}
<?php

require_once '../interfaces/PostOffice.php';
require_once 'testData.php';
echo simpleSignMessage($password, $messageBody);
echo simpleCheckMessageSignature($password, $messageBody, simpleSignMessage($password, $messageBody));
function signMessage($password, $body)
{
    return simpleSignMessage($password, $body);
}