  We investigate the problem of reliable communication in the presence of
active adversaries that can tamper with the transmitted data. We consider a
legitimate transmitter-receiver pair connected over multiple communication
paths (routes). We propose two new models of adversary, a "memoryless" and a
"foreseer" adversary. For both models, the adversaries are placing themselves
arbitrarily on the routes, keeping their placement fixed throughout the
transmission block. This placement may or may not be known to the transmitter.
The adversaries can choose their best modification strategy to increase the
error at the legitimate receiver, subject to a maximum distortion constraint.
We investigate the communication rates that can be achieved in the presence of
the two types of adversaries and the channel (benign) stochastic behavior. For
memoryless adversaries, the capacity is derived. Our method is to use the
typical set of the anticipated received signal for all possible adversarial
strategies (including their best one) in a compound channel that also captures
adversarial placement. For the foreseer adversaries, which have enhanced
observation capabilities compared to the memoryless ones, we propose a new
coding scheme to guarantee resilience, i.e., recovery of the codeword
independently of the adversarial (best) choice. We derive an achievable rate
and we propose an upper bound on the capacity. We evaluate our general results
for specific cases (e.g., binary symbol replacement or erasing attacks), to
gain insights.
