Quantum cryptography: Public key distribution and coin tossing

TL;DR

This paper explores how quantum systems enable secure cryptographic tasks like key distribution and coin tossing, leveraging quantum uncertainty to detect eavesdropping and achieve security beyond classical capabilities.

Contribution

It introduces quantum cryptographic protocols for secure key distribution and coin tossing, highlighting their security advantages and limitations due to quantum phenomena.

Findings

Quantum channels allow eavesdrop detection during key distribution.

Quantum coin tossing protocols are secure against classical cheating.

EPR paradox can undermine quantum coin-tossing security.

Abstract

When elementary quantum systems, such as polarized photons, are used to transmit digital information, the uncertainty principle gives rise to novel cryptographic phenomena unachievable with traditional transmission media, e.g. a communications channel on which it is impossible in principle to eavesdrop without a high probability of disturbing the transmission in such a way as to be detected. Such a quantum channel can be used in conjunction with ordinary insecure classical channels to distribute random key information between two users with the assurance that it remains unknown to anyone else, even when the users share no secret information initially. We also present a protocol for coin-tossing by exchange of quantum messages, which is secure against traditional kinds of cheating, even by an opponent with unlimited computing power, but ironically can be subverted by use of a still subtler quantum phenomenon, the Einstein-Podolsky-Rosen paradox.