Modified Quantum Three Pass Protocol Based on Hybrid Cryptosystem

In this thesis we propose an enhancement to the Quantum Three-Pass Protocol (QTPP) by adding quantum authentication. After detailed analysis of all possible classical as well as quantum attack methods of the original Quantum Three-Pass Protocol, we identified, that the original Quantum Three-Pass Protocol is only vulnerable against the man-in-the-middle attack. By adding authentication and an agent called the Quantum Distribution Centre, the man-in-the-middle attack is eliminated. All communication between the parties is established over quantum channels with non-orthogonal superposition states that are subject to the no-cloning theorem. The security analysis shows that the modified Quantum Three Pass Protocol is unconditionally secure in the sense that the key is random, the protocol is authenticated, and all communication channels are subject to quantum physics. Furthermore, the bit error rate as a function of the noise on the channel is discussed.Using the enhanced QTPP a complete encryption process is designed exploiting also classical algorithms.