Signals intelligence

Signals intelligence (SIGINT) is intelligence-gathering by interception of signals, whether between people (i.e., communications intelligence (COMINT)) or between machines (i.e., electronic intelligence (ELINT)), or mixtures of the two. As sensitive information is often encrypted, signals intelligence often involves the use of cryptanalysis. However, traffic analysis &mdash; the study of who is signalling whom and in what quantity &mdash; can often produce valuable information, even when the messages themselves cannot be decrypted.