Cryptanalysis of a Practical Quantum Key Distribution With   Polarization-Entangled Photons
  Recently, a quantum key exchange protocol has been described, which served as basis for securing an actual bank transaction by means of quantum cryptography [quant-ph/0404115]. Here we show, that the authentication scheme applied is insecure in the sense that an attacker can provoke a situation where initiator and responder of a key exchange end up with different keys. Moreover, it may happen that an attacker can decrypt a part of the plaintext protected with the derived encryption key. 
Thomas Beth and Joern Mueller-Quade and Rainer Steinwandt