CIF: Small: Causal Secrecy-A Theoretical Basis for Secrecy of Signals

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Communication technologies have taken a central role in daily life, business, government, industry, and social interactions over recent decades. Technology is used not only to allow people to communicate with each other from across the world but to allow machines to interact automatically---processing internet search queries, managing warehouse inventory, forecasting severe weather, updating computer software, and controlling complex systems such as a network of electric power stations. The need for secure communication has increased accordingly. Currently, technology is designed around the concept that a secure or private communication signal must be invisible to the outside world unless the security is compromised. This matches the Hollywood image of a top-secret classified conversation taking place over a "secure line." However, in many emerging applications where machines transmit important information signals to each other, a less expensive type of privacy is adequate---one that simply distorts the view of the signal for any unintended eavesdroppers to the point where they cannot use the information to disrupt the system. This research involves a mathematical analysis of the secrecy of signals. The investigators derive fundamental minimum requirements to protect the communication of signals.This research uses information theory to provide a theoretical foundation for secrecy of signals, using secret keys and physical layer security. However, this work differs from previous theoretical work in a number of ways. One key difference is that metrics for secrecy based on abstract or intangible mathematical quantities are omitted. Instead, secrecy is evaluated based on what an adversary would be able to do with information gleaned from the system. This research is theoretical and broad, yet the novelty of the results bring new insights to applied cryptography.