The uncloneable bit exists

TL;DR

This paper proves the existence of an uncloneable bit in quantum physics, establishing unconditionally secure quantum encryption that prevents multiple adversaries from decrypting a ciphertext simultaneously, even with the key.

Contribution

It introduces a novel quantum encryption scheme with unconditional security, leveraging quantum information principles and monogamy of entanglement, without relying on assumptions.

Findings

Achieves security approaching the ideal exponentially in the security parameter

Demonstrates the existence of an uncloneable bit in Nature

Provides a fundamental cryptographic primitive unavailable classically

Abstract

We establish quantum uncloneable encryption with unconditional security, preventing two non-communicating adversaries from simultaneously decrypting a single ciphertext $-$ even when both are given the key. Our construction achieves security that approaches the ideal limit at a rate that is exponentially small in the security parameter, without employing any assumptions. Our proof invokes quantum information principles in the fully quantum realm, in a novel setting of cryptography. A decoupling step certifies the statistical independence needed for randomness extraction, and monogamy of entanglement, formalised via strong subadditivity, rules out the sender being highly correlated with two non-communicating adversaries at once. Consequently, no coordinated strategy beats random guessing of the encrypted bit, establishing unconditional uncloneability. This reveals the existence of an uncloneable bit in Nature and delineates a fundamental, physically enforced cryptographic primitive unavailable in classical settings.