private byte[] GetMessageBytesToSign()
{
string stringToSign = null;
if (this.IsNotificationType)
stringToSign = BuildNotificationStringToSign();
else if (this.IsSubscriptionType || this.IsUnsubscriptionType)
stringToSign = BuildSubscriptionStringToSign();
else
throw new AmazonClientException("Unknown message type: " + this.Type);
byte[] bytesToSign = UTF8Encoding.UTF8.GetBytes(stringToSign);
return bytesToSign;
}