Abstract: The present invention provides an improved method and apparatus for authenticating message packets to prevent forgery thereof. A server processes a client request and generates a response message. A message signature, which is generated using the session key and the message itself, is appended to the message to create an appended message. The server sends the appended message to the client. At the same time that the server works on the client request, the client predicts the response message and calculates a predicted message signature based on the session key and the predicted message. After receiving the appended message, the client strips the message signature from the appended message and compares it to the predicted message signature. If the two signatures match, the received message packet is authenticated.