Quantum cryptography is the use of quantum mechanicalproperties to perform cryptographic tasks. The best known example of quantum cryptography is quantum key distribution which provides a solution to the breaking of various popular public-key encryption and signature schemes (e.g., RSA and ElGamal). The advantage of quantum cryptography lies in the fact that it allows the completion of various cryptographic tasks that are proven or conjectured to be impossible using only classical (i.e.