Traditional cryptographic solutions implicitly assume an offline key distribution mechanism and focus on encryption when the sender and receiver have a common key not available to an eavesdropper. Many emerging applications challenge this assumption. One application is pay TV broadcast, where it is desirable to encrypt each program with a separate key so that only users who pay for a certain program can view it. The key must be useless once the broadcast of a particular program terminates. Another application is sensor networks. It is desirable toperiodically update the key so that key cannot be stolen from the nodes.
In this work, we study efficient mechanism to distribute keys in a wireless medium. We model the problem as a transmitter with multiple antennas intending to broadcast a key to a receiver or a group of receivers under the constraint that an eavesdropper cannot decode the key. The approaches investigate the importance of artificial noise, opportunistic communication and smart array processing for this application.