Introducing Traffic Analysis

In the Second World War, traffic analysis was used by the British at Bletchley Park to assess the size of Germany’s air-force, and Japanese traffic analysis countermeasures contributed to the surprise of their 1941 attack on Pearl Harbour. Nowadays, Google uses the incidence of links to assess the relative importance of web pages, credit card companies examine transactions to spot fraudulent patterns of spending, and amateur plane-spotters revealed the CIA’s ‘extraordinary rendition’ programme. Diffie and Landau, in their book on wiretapping, went so far as to say that “traffic analysis, not cryptanalysis, is the backbone of communications intelligence” [1]. However, until recently the topic has been neglected by Computer Science academics. A rich literature discusses how to secure the confidentiality, integrity and availability of communication content, but very little work has considered the information leaked from communications ‘traffic data’ and how these compromises might be minimised. Traffic data records the time and duration of a communication, and traffic analysis examines this data to determine the detailed shape of the communication streams, the identities of the parties communicating, and what can be established about their locations. The data may even be sketchy or incomplete – simply knowing what ‘typical’ communication patterns look like can be used to infer information about a particular observed communication. Civilian infrastructures, on which state and economic actors are increasingly reliant, are ever more vulnerable to traffic analysis: wireless and GSM telephony are replacing traditional systems, routing is transparent and protocols are overlaid over others – giving plenty of opportunity to observe, and take advantage of the traffic data. Concretely, an attacker can make use of this