Existing navigation services, such as GPS, offer no signal-integrity (anti-spoof) protection for the general public, especially not with systems for remote attestation of location, where an attacker has easy access to the receiver antenna. With predictable broadcast signals, the antenna can be replaced with a signal generator that simulates a signal as it would be received elsewhere. With a symmetrically encrypted broadcast signal, anyone who can build or reverse engineer a receiver will know the secret key needed to spoof other receivers. Such encryption is only of use in closed user communities (e.g., military) or with highly tamper-resistant modules protecting the common key. In open user communities without common secret keys, integrity protection is needed instead, with properties similar to digital signatures. The ability to verify a navigation signal must be separate from the ability to generate a new one or to apply selective-delay attacks; but simply signing the broadcast signals will not protect their exact relative arrival times. This paper introduces a practical solution based on short-term information hiding.
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