Unforgeable Quantum Encryption

TL;DR

This paper introduces new definitions and constructions for secure quantum encryption that prevent forgery and authenticate quantum data, overcoming classical limitations like no-cloning, and establishing a foundation for quantum cryptographic security.

Contribution

It develops novel quantum security notions, uses entanglement to detect cheating, and constructs schemes satisfying these new security definitions, including a new approach to quantum authentication.

Findings

Quantum encryption schemes achieve ciphertext unforgeability.

New quantum security notions imply classical security properties.

Constructed schemes satisfy multiple quantum security definitions.

Abstract

We study the problem of encrypting and authenticating quantum data in the presence of adversaries making adaptive chosen plaintext and chosen ciphertext queries. Classically, security games use string copying and comparison to detect adversarial cheating in such scenarios. Quantumly, this approach would violate no-cloning. We develop new techniques to overcome this problem: we use entanglement to detect cheating, and rely on recent results for characterizing quantum encryption schemes. We give definitions for (i.) ciphertext unforgeability , (ii.) indistinguishability under adaptive chosen-ciphertext attack, and (iii.) authenticated encryption. The restriction of each definition to the classical setting is at least as strong as the corresponding classical notion: (i) implies INT-CTXT, (ii) implies IND-CCA2, and (iii) implies AE. All of our new notions also imply QIND-CPA privacy. Combining one-time authentication and classical pseudorandomness, we construct schemes for each of these new quantum security notions, and provide several separation examples. Along the way, we also give a new definition of one-time quantum authentication which, unlike all previous approaches, authenticates ciphertexts rather than plaintexts.