  Secure communication over a wiretap channel is considered in the
disadvantaged wireless environment, where the eavesdropper channel is (possibly
much) better than the main channel. We present a method to exploit inherent
vulnerabilities of the eavesdropper's receiver to obtain everlasting secrecy.
Based on an ephemeral cryptographic key pre-shared between the transmitter
Alice and the intended recipient Bob, a random jamming signal is added to each
symbol. Bob can subtract the jamming signal before recording the signal, while
the eavesdropper Eve is forced to perform these non-commutative operations in
the opposite order. Thus, information-theoretic secrecy can be obtained, hence
achieving the goal of converting the vulnerable "cheap" cryptographic secret
key bits into "valuable" information-theoretic (i.e. everlasting) secure bits.
We evaluate the achievable secrecy rates for different settings, and show that,
even when the eavesdropper has perfect access to the output of the transmitter
(albeit through an imperfect analog-to-digital converter), the method can still
achieve a positive secrecy rate. Next we consider a wideband system, where
Alice and Bob perform frequency hopping in addition to adding the random
jamming to the signal, and we show the utility of such an approach even in the
face of substantial eavesdropper hardware capabilities.
