  We study communication in the presence of a jamming adversary where quadratic
power constraints are imposed on the transmitter and the jammer. The jamming
signal is allowed to be a function of the codebook, and a noncausal but noisy
observation of the transmitted codeword. For a certain range of the
noise-to-signal ratios (NSRs) of the transmitter and the jammer, we are able to
characterize the capacity of this channel under deterministic encoding or
stochastic encoding, i.e., with no common randomness between the
encoder/decoder pair. For the remaining NSR regimes, we determine the capacity
under the assumption of a small amount of common randomness (at most $2\log(n)$
bits in one sub-regime, and at most $\Omega(n)$ bits in the other sub-regime)
available to the encoder-decoder pair. Our proof techniques involve a novel
myopic list-decoding result for achievability, and a Plotkin-type push attack
for the converse in a subregion of the NSRs, both of which which may be of
independent interest. We also give bounds on the secrecy capacity of this
channel assuming that the jammer is simultaneously eavesdropping.
