signals intelligence

RAF Menwith Hill, a large site in the United Kingdom, part of ECHELON and the UKUSA Agreement in 2005 A German message intercepted by the British during World War II, signaling Germany's unconditional surrender

Signals intelligence (SIGINT) is the act and field of intelligence-gathering by interception of signals, whether communications between people (communications intelligence—abbreviated to COMINT) or from electronic signals not directly used in communication (electronic intelligence—abbreviated to ELINT). As classified and sensitive information is usually encrypted, signals intelligence may necessarily involve cryptanalysis (to decipher the messages). Traffic analysis—the study of who is signaling to whom and in what quantity—is also used to integrate information, and it may complement cryptanalysis.