Routers and modems can read the contents of packets they relay. To protect confidentiality on the Internet, we should thus use encryption to make our messages look like nonsense to outsiders. In this level, we introduce a simple encryption protocol that allows two parties to communicate privately.

This "encryption" protocol involves packets with three different types of messages (specified at the application layer):

• keyrequest is used to specify one's own key and request the other party's key.
• keyresponse is a response to a keyrequest and includes only one's own key.
• After these first two steps have occurred, the two parties can exchange message packets, encrypted with the recipient's key.

To pass this level, send an encrypted message from Alice's computer to Bob's computer. You must first have Alice and Bob exchange keys. Alice's encryption key is 12345.

Hint: there is an example of how the encryption protocol works at the top of the field. Use the pause button to see what the values of the packet headers are in the protocol.

Level Objectives

• have Alice and Bob exchange encryption keys
• send an encrypted message from Alice to Bob