[Paper Review] Quantum cryptography: Public key distribution and coin tossing

C. H. Bennett, Brassard, Gilles|arXiv (Cornell University)|Mar 14, 2020

Chaos-based Image/Signal EncryptionComputer Science5,308 citations

TL;DR

The paper explains how quantum channels enable secure public key distribution (quantum key distribution) and a quantum coin-tossing protocol, with security against conventional cheating but vulnerability to certain quantum paradoxes.

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.

Motivation & Objective

• Motivate how uncertainty in quantum systems enables eavesdropping detection in communications.
• Describe a protocol for distributing random key information using quantum channels and insecure classical channels.
• Introduce a quantum coin-tossing protocol secure against classical cheating.
• Discuss limitations and potential quantum paradox weaknesses in cryptographic tasks.

Proposed method

• Describe use of elementary quantum systems (e.g., polarized photons) to transmit information.
• Explain how an eavesdropper would necessarily disturb the transmission, enabling detection.
• Outline a protocol for quantum key distribution with an insecure classical channel.
• Present a quantum coin-tossing protocol secure against traditional cheating strategies.
• Note the potential subversion by the Einstein-Podolsky-Rosen paradox.

Experimental results

Research questions

• RQ1 Can quantum channels enable secure distribution of key information when paired with insecure classical channels?
• RQ2 Is it possible to implement a coin-tossing protocol that remains secure against unlimited-power adversaries?
• RQ3 What limitations exist in quantum cryptographic protocols due to quantum phenomena such as entanglement?

Key findings

• Quantum channels allow distribution of random key information unknown to others, even without initial shared secrets.
• A coin-tossing protocol via quantum messages is secure against traditional cheating and unlimited-power adversaries.
• However, the protocol can be subverted by exploiting the Einstein-Podolsky-Rosen paradox, revealing limits due to deeper quantum phenomena.