On Split-State Quantum Tamper Detection and Non-Malleability
Thiago Bergamaschi, Naresh Goud Boddu
TL;DR
The paper advances quantum tamper-detection by showing that a multipartite quantum encoding across at least $3$ shares enables tamper-detection against split-state tampering with bounded entanglement, a feat impossible for classical codes. It provides a concrete 3-split tamper-detection code with constant rate and inverse-subexponential error in the bounded-storage regime, built from quantum-secure non-malleable extractors and unitary 2-designs. Beyond the code itself, the authors develop a blueprint to turn these codes into tamper-detecting secret sharing schemes and establish links to quantum encryption/authentication, highlighting how tamper-detection naturally implies a form of encryption of shares. They also connect their constructions to leakage-resilient secret sharing and to non-malleable quantum encryption notions, yielding a framework that unifies tamper-resilience, secret sharing, and encryption in the quantum setting. The work raises open questions about optimal capacity, LOCC tamper-detection, and extensions to quantum secrets, while providing concrete building blocks for tamper-detecting quantum cryptographic primitives with practical rate and security guarantees.
Abstract
Tamper-detection codes (TDCs) are fundamental objects at the intersection of cryptography and coding theory. A TDC encodes messages in such a manner that tampering the codeword causes the decoder to either output the original message, or reject it. In this work, we study quantum analogs of one of the most well-studied adversarial tampering models: the so-called $t$-split-state tampering model, where the codeword is divided into $t$ shares, and each share is tampered with "locally". It is impossible to achieve tamper detection in the split-state model using classical codewords. Nevertheless, we demonstrate that the situation changes significantly if the message can be encoded into a multipartite quantum state, entangled across the $t$ shares. Concretely, we define a family of quantum TDCs defined on any $t\geq 3$ shares, which can detect arbitrary split-state tampering so long as the adversaries are unentangled, or even limited to a finite amount of pre-shared entanglement. Previously, this was only known in the limit of asymptotically large $t$. As our flagship application, we show how to augment threshold secret sharing schemes with similar tamper-detecting guarantees. We complement our results by establishing connections between quantum TDCs and quantum encryption schemes.
