On secure communication over the multiple access channel

This paper studies the problem of secure communication over a 2-transmitter multiple access channel (MAC) in the presence of an external eavesdropper. Two different secrecy constraints are considered: 1) individual secrecy (i.e., information leakage rate from each message to the eavesdropper is made vanishing) and 2) joint secrecy (i.e., information leakage rate from both messages to the eavesdropper is made vanishing). As a general result, the respective achievable secrecy rate regions are established. The single-letter characterizations of both regions involve three auxiliary random variables, one for time sharing and two for channel prefixing. Numerical results are presented to demonstrate the impact of different secrecy constraints and the advantage of channel prefixing in enlarging the achievable (individual/joint) secrecy rate regions.