关键词：电子信息；信息安全；物理层；通信系统
摘 要：So far, we have introduced protections of communication systems placed at the upper layers of networked communication systems. Those mechanisms utilize modern cryptographic methods, together with network administration policies. The important characteristics of modern cryptographic algorithms and protocols are that they are independent of physical-layer transmission technologies and assume that the physical-layer transmission has already been established and is error free.