Paper 2016/1122

Quantum Key Recycling with eight-state encoding (The Quantum One Time Pad is more interesting than we thought)

B. Skoric and M. de Vries

Abstract

Perfect encryption of quantum states using the Quantum One-Time Pad (QOTP) requires 2 classical key bits per qubit. Almost-perfect encryption, with information-theoretic security, requires only slightly more than 1. We slightly improve lower bounds on the key length. We show that key length n+2log1ε suffices to encrypt n qubits in such a way that the cipherstate's L1-distance from uniformity is upperbounded by ε. For a stricter security definition involving the -norm, we prove sufficient key length n+logn+2log1ε+1+1nlog1δ+logln21ε, where δ is a small probability of failure. Our proof uses Pauli operators, whereas previous results on the -norm needed Haar measure sampling. We show how to QOTP-encrypt classical plaintext in a nontrivial way: we encode a plaintext bit as the vector on the Bloch sphere. Applying the Pauli encryption operators results in eight possible cipherstates which are equally spread out on the Bloch sphere. This encoding, especially when combined with the half-keylength option of QOTP, has advantages over 4-state and 6-state encoding in applications such as Quantum Key Recycling and Unclonable Encryption. We propose a key recycling scheme that is more efficient and can tolerate more noise than a recent scheme by Fehr and Salvail. For 8-state QOTP encryption with pseudorandom keys we do a statistical analysis of the cipherstate eigenvalues. We present numerics up to 9 qubits.

Note: Improved the Key Recycling scheme. Extended the results on key length.

Metadata
Available format(s)
PDF
Publication info
Preprint. MINOR revision.
Keywords
quantum cryptography
Contact author(s)
b skoric @ tue nl
History
2016-12-29: last of 3 revisions
2016-12-01: received
See all versions
Short URL
https://ia.cr/2016/1122
License
Creative Commons Attribution
CC BY

BibTeX

@misc{cryptoeprint:2016/1122,
      author = {B.  Skoric and M.  de Vries},
      title = {Quantum Key Recycling with eight-state encoding (The Quantum One Time Pad is more interesting than we thought)},
      howpublished = {Cryptology {ePrint} Archive, Paper 2016/1122},
      year = {2016},
      url = {https://eprint.iacr.org/2016/1122}
}
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