Adversary-induced keystream re-use on TETRA air-interface encrypted traffic using any TEA keystream generator. IV generation is based upon several TDMA frame counters, which are frequently broadcast by the infrastructure in an unauthenticated manner. An active adversary can manipulate the view of these counters in a mobile station, provoking keystream re-use. By sending crafted messages to the MS and analyzing MS responses, keystream for arbitrary frames can be recovered.