Codes for Key Generation in Quantum Cryptography
  As an alternative to the usual key generation by two-way communication in schemes for quantum cryptography, we consider codes for key generation by one-way communication. We study codes that could be applied to the raw key sequences that are ideally obtained in recently proposed scenarios for quantum key distribution, which can be regarded as communication through symmetric four-letter channels. 
Berthold-Georg Englert, Fang-Wei Fu, Harald Niederreiter, Chaoping   Xing