A Quantum Cryptosystem Secure Against Beamsplitting Attacks

An important area in computer and communications security research is to make various pioneering ideas practical. In this paper we develop a new cryptographic key distribution system based on the uncertainty principle in quantum physics. The new system employs a novel technique that mixes two quantum states in the transmission of photonic signals. On one hand, this technique forces an eavesdropper to extract more signal energy in an eavesdropping process, which renders an eavesdropping attempt easily detectable. And on the other hand,it allows legitimate communicants to transmit higher power photonic signals, whereby secure communications are made possible over a signiicantly longer haul than any other system based on the same principle could support. Another contribution of this paper is to present a new powerful attack based on a pair of beamsplitters. We show that while a well-known quantum key distribution system proposed previously is prone to the new attack, our system is immune to it.