  This paper studies a new active eavesdropping technique via the so-called
spoofing relay attack, which could be launched by the eavesdropper to
significantly enhance the information leakage rate from the source over
conventional passive eaves-dropping. With this attack, the eavesdropper acts as
a relay to spoof the source to vary transmission rate in favor of its
eavesdropping performance by either enhancing or degrading the effective
channel of the legitimate link. The maxi-mum information leakage rate
achievable by the eavesdropper and the corresponding optimal operation at the
spoofing relay are obtained. It is shown that such a spoofing relay attack
could impose new challenges from a physical-layer security perspective since it
leads to significantly higher information leakage rate than conventional
passive eavesdropping.
