Due to their large size, video images present a great challenge to currently available cryptographic algorithms; the computationally intensive processes of encryption and decryption of video images, introduce delays that are beyond acceptable real-time video application limits. In this paper, the Aegis mechanism is proposed.Aegis limits the amount of data to be encrypted or decrypted by using video compression to reduce the size of transmitted video images. The performance of Aegis (utilizing MPEG video compression across an ATM network) is explored through an extensive simulation study. Three types of video traffic: CATV, Studio TV, and video conference are considered. Our simulation results demonstrate the delay performance, as well as, the queue requirements for the Aegis encryption scheme versus the full encryption and no encryption schemes.