Paper 2017/331

Optimal attacks on qubit-based Quantum Key Recycling

Daan Leermakers and Boris Skoric


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.

Available format(s)
Publication info
Preprint. MINOR revision.
quantum cryptographyquantum key recycling
Contact author(s)
b skoric @ tue nl
2017-04-17: received
Short URL
Creative Commons Attribution


      author = {Daan Leermakers and Boris Skoric},
      title = {Optimal attacks on qubit-based Quantum Key Recycling},
      howpublished = {Cryptology ePrint Archive, Paper 2017/331},
      year = {2017},
      note = {\url{}},
      url = {}
Note: In order to protect the privacy of readers, does not use cookies or embedded third party content.