Sealed States And Quantum Blackmail

TL;DR

This paper explores the limitations of quantum cryptography in secure message sealing and proposes that combining quantum methods with human-invertible functions like CAPTCHAs can exponentially enhance security.

Contribution

It proves the inherent weakness of standard quantum cryptographic protocols and introduces a novel approach combining quantum cryptography with CAPTCHAs for stronger security.

Findings

Quantum protocols have weak security guarantees.

Combining quantum cryptography with CAPTCHAs can exponentially improve security.

Classical cryptography alone cannot prevent message copying.

Abstract

Consider a protocol in which Belinda seals a (classical) message. She gives the resulting sealed message to Charlie, who can either unseal and read the message or return it unopened to Belinda. If he returns it unopened, Belinda should be able to verify that Charlie neither read the message nor made a copy that would allow him to read it later. Such a protocol is impossible with classical cryptography: Charlie can copy a message and do anything he likes to that copy without damaging the original. With quantum cryptography, on the other hand, the no cloning theorem implies that Charlie cannot simply copy a message and unseal the copy. Abstract In this paper, I prove that any conventional quantum cryptographic protocol can give at best a very weak security guarantee. However, quantum cryptography in conjunction with classical functions that can only be inverted by humans (i.e. CAPTCHAs) can potentially give exponential security.