Measures and controls taken to deny unauthorized persons information derived from telecommunications and ensure the authenticity of such telecommunications. Communications security includes cryptosecurity, transmission security, emission security, traffic-flow security. and physical security of COMSEC material.

• cryptosecurity: The component of communications security that results from the provision of technically sound cryptosystems and their proper use. This includes insuring message confidentiality and authenticity.
• emission security (EMSEC): Protection resulting from all measures taken to deny unauthorized persons information of value which might be derived from intercept and analysis of compromising emanations from crypto-equipment, automated information systems (computers), and telecommunications systems.
• physical security: The component of communications security that results from all physical measures necessary to safeguard classified equipment, material, and documents from access thereto or observation thereof by unauthorized persons.
• traffic-flow security: Measures that conceal the presence and properties of valid messages on a network. It includes the protection resulting from features, inherent in some crypto equipment, that conceal the presence of valid messages on a communications circuit, normally achieved by causing the circuit to appear busy at all times.
• transmission security (TRANSEC): The component of communications security that results from the application of measures designed to protect transmissions from interception and exploitation by means other than cryptanalysis (e.g. frequency hopping and spread spectrum).