Cryptology ePrint Archive: Report 2017/331

Optimal attacks on qubit-based Quantum Key Recycling

Daan Leermakers and Boris Skoric

Abstract: Quantum Key Recycling (QKR) is a quantum-cryptographic primitive that allows one to re-use keys in an unconditionally secure way. By removing the need to repeatedly generate new keys it improves communication efficiency. Škorić and de Vries recently proposed a QKR scheme based on 8-state encoding (four bases). It does not require quantum computers for encryption/decryption but only single-qubit operations. We provide a missing ingredient in the security analysis of this scheme in the case of noisy channels: accurate bounds on the privacy amplification. We determine optimal attacks against the message and against the key, for 8-state encoding as well as 4-state and 6-state conjugate coding. We show that the Shannon entropy analysis for 8-state encoding reduces to the analysis of Quantum Key Distribution, whereas 4-state and 6-state suffer from additional leaks that make them less effective. We also provide results in terms of the min-entropy. Overall, 8-state encoding yields the highest capacity.

Category / Keywords: quantum cryptography, quantum key recycling

Date: received 13 Apr 2017

Contact author: b skoric at tue nl

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Version: 20170417:160536 (All versions of this report)

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