The forthcoming release of quantum computers, as also the advances of classical computers, may threaten most of the cryptosystems used today, in particular the asymmetric ones. Although new and more secure cryptosystems can be developed, the best long-term solution is quantum cryptography. Nowadays, the first Quantum Key Distribution (QKD) systems are already on the market. QKD is employed in symmetric encryption schemes, like “one-time pad”, and it ideally permits to obtain unconditionally secure communications, exploiting properties of quantum mechanics such as the no-cloning theorem. The private key is exchanged as a stream of single-photon pulses encoding the quantum information (qubits). In this thesis a simulation framework for QKD systems based on polarization encoding is presented.