Semi-Quantum Key Distribution

TL;DR

This paper explores semi-quantum key distribution protocols where only one party is quantum and proves their robustness against eavesdropping, extending previous results and introducing new protocols based on randomization.

Contribution

It introduces two new semi-quantum key distribution protocols and proves their robustness against attacks, generalizing previous results and enhancing security analysis.

Findings

Protocols are robust against eavesdropping attempts.

Any information gain by an adversary induces detectable errors.

One protocol is based on randomization, offering a novel approach.

Abstract

Secure key distribution among two remote parties is impossible when both are classical, unless some unproven (and arguably unrealistic) computation-complexity assumptions are made, such as the difficulty of factorizing large numbers. On the other hand, a secure key distribution is possible when both parties are quantum. What is possible when only one party (Alice) is quantum, yet the other (Bob) has only classical capabilities? Recently, a semi-quantum key distribution protocol was presented (Boyer, Kenigsberg and Mor, Physical Review Letters, 2007), in which one of the parties (Bob) is classical, and yet, the protocol is proven to be completely robust against an eavesdropping attempt. Here we extend that result much further. We present two protocols with this constraint, and prove their robustness against attacks: we prove that any attempt of an adversary to obtain information (and even a tiny amount of information) necessarily induces some errors that the legitimate parties could notice. One protocol presented here is identical to the one referred to above, however, its robustness is proven here in a much more general scenario. The other protocol is very different as it is based on randomization.