The performance analysis of a multiple-antenna wiretap channel is studied with the variation of the number of antennas at the transmitting, receiving and the eavesdropping ends. The function of multiple antennas for protected communication is investigated within the outline of Wyner's wiretap channel. We exemplify the secrecy capacity in terms of generalized eigen values when the sender, eavesdropper and the receiver have multiple antennas. The secrecy rates are compared with the change in the number of antennas used. Energy requirements under secrecy constraints are quantified. Energy efficiency is estimated by determining the minimum bit energy required for protected and trustworthy communications. © Research India Publications.