  This article presents a novel method for establishing an information
theoretically secure encryption key over wireless channels. It exploits the
fact that data transmission over wireless links is accompanied by packet error,
while noise terms, and thereby the error events observed by two separate
receivers are independent of each other. A number of data packets, with random
data, are transmitted from a first legitimate node, say Alice, to a second
legitimate node, say Bob. Bob identifies all packets that are received
error-free in the first transmission attempt and sends their indices to Alice
over a public channel. Then, both Alice and Bob mix the contents of identified
packets, e.g., using a hash function, and thereby derive an identical
encryption key. Since error events from Alice to Bob is independent of error
events from Alice to Eve, the chances that Eve has successfully received all
packets used in key generation error-free diminishes as the number of packet
increases. In many wireless standards, the first stage in error detection and
Automatic Repeat Request (ARQ) is deployed at the PHY/MAC (Physical
Layer/Medium Access Control) layer. In such setups, the first re-transmission
is manged by the PHY/MAC layer without informing higher layers. This makes it
impossible to directly access the information related to packet errors through
high-level programming interfaces available to an end-user. A method is
presented for determining packets received error-free in first transmission
attempts through high-level programming. Examples are presented in conjunction
with an LTE cellular network.
