function simpleReceiveEnvelopeAndGiveReceipt($envelope, $password)
{
    $message = getMessageFromEnvelope($envelope);
    $messageName = getMessageNameFromMessage($message);
    $authorName = getAuthorNameFromMessage($message);
    $messageHeader = array();
    $messageHeader['messageName'] = $messageName;
    $messageHeader['authorName'] = $authorName;
    $messageBody = getMessageBodyFromMessage($message);
    $signature = getSignatureFromMessage($message);
    $signatureCheckStatus = checkMessageSignature($password, $messageBody['body'], $signature);
    if (!$signatureCheckStatus) {
        $exchangeStatus = 'EXCHANGE_FAILED';
        $exchangeReceipt = createExchangeReceipt($signatureCheckStatus, $exchangeStatus, null, null);
        $messageBody['body'] = writeExchangeReceipt($exchangeReceipt);
        $message = createMessage($messageHeader, $messageBody);
        return putMessageIntoEnvelope($message, $messageHeader);
    }
    $exchangeReceipt = receiveMessageAndGiveReceipt($messageHeader, $messageBody);
    $messageBody['body'] = writeExchangeReceipt($exchangeReceipt);
    $message = createMessage($messageHeader, $messageBody);
    return putMessageIntoEnvelope($message, $messageHeader);
}
<?php

require_once '../interfaces/PostOffice.php';
require_once 'testData.php';
echo getSignatureFromMessage($message);