Exploiting multiple side channels for secret key agreement in Wireless Networks.

Generating a secret key between two wireless devices without any priori information is a challenging problem. Extracting the shared secret from a wireless fading channel is proven as an effective solution to this problem. However, the unreliable wireless channel results in a significant communication overhead. Most of the related works focus on minimizing the impact of channel unreliability in the key agreement process. In this paper, we explore another direction, multiple side channels, to establish the shared key in wireless networks. In the context of network security, side channels are a way to steal sensitive information from computer network system. However, they can also be used in the hidden information exchange such as key agreement protocol. In our design, one of the side channels is packet transmission power. By switching among multiple transmission power levels, the receiver is able to decode the bits by comparing the Received Signal Strength (RSS) of the current packet with that of the previous one. However, a side channel of transmission power changes alone is not sufficiently secure as adversary could intercept the packets and infer the transmission power change pattern. Therefore, we employ another side channel by swapping the source and Destination address of the packets. We showed that adversary is able to extract shared bit with only one of the these side channels deployed but cannot when both side channels are utilized. We showed that our approach could establish the N-bit shared key with O(N) packets.