Traffic-flow security is the use of measures that conceal the presence and properties of valid messages on a network to prevent traffic analysis. This can be done by operational proceedures or by the protection resulting from features inherent in some cryptographic equipment. Techniques used include:

• changing radio callsigns frequently
• encryption of a message's sending and receiving addresses (codress messages)
• causing the circuit to appear busy at all times or much of the time by sending dummy traffic
• sending a continuous encrypted signal, whether or not traffic is being transmitted.

Traffic-flow security is one aspect of communications security.