Wireless link signature is a physical layer authentication mechanism, which uses the multi-path effect between a transmitter and a receiver to provide authentication of wireless signals. We identify a new attack, called mimicry attack, against the wireless link signature scheme in [7] . It is assumed in the past that an attacker cannot "spoof" an arbitrary link signature and that the attacker will not have the same link signature at the receiver unless it is at exactly the same location as the

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... egitimate transmitter. However, we show that an attacker can forge an arbitrary link signature as long as it knows the legitimate signal at the receiver's location, and the attacker does not have to be at exactly the same location as the legitimate transmitter in order to forge its link signature.