Communication security (COMSEC) prevents unauthorized access to data transmission and transmitted information. Communication security includes cryptography, emission security, transmission security and physical security and, together with computer security( COMPUSEC), forms information security( INFOSEC).
Through cryptography, the transmitted data is encrypted and therefore cannot be interpreted by unauthorized persons. Only after decryption can they be read again. The content of encrypted data remains confidential.
Emission security (EMSEC) prevents the interception and analysis of compromising radiation by attackers who can filter the information contained in the emitted radiation. Appropriate emissions can be emitted from both the physical medium and the information systems.
Physical security prevents unauthorized persons from accessing the network and the encrypted data, documents and devices.
Transmission security protects the transmission links. It prevents interception of messages in the transmission channel and over radio links. Transmission security includes techniques other than encryption of information. For example, radio transmission techniques such as frequency hopping or spread spectrum technology.