Fund Project:Project supported by the National Natural Science Foundation of China (Grant Nos. 61871407, 61572529, 61872390), the Fundamental Research Funds for the Central Universities of Central South University, China (Grant No. 2018zzts179), and the Natural Science Foundation of Hunan Province, China (Grant No. 2017JJ3415).
Received Date:27 February 2019
Accepted Date:15 April 2019
Available Online:01 June 2019
Published Online:20 June 2019
Abstract:Quantum signature is quantum counterpart of classical digital signature, which has been widely applied to modern communication, such as electronic payment, electronic voting and electronic medical, owing to its great implication in ensuring the authenticity and the integrity of the message and the non-repudiation. Arbitrated quantum signature (AQS) is an important and practical type of quantum signature. The AQS algorithm is a symmetric key cryptography-based quantum signature algorithm, and its implementation requires the trusted arbitrator to be directly involved. In this paper, employing the key-controlled chained CNOT (KCCC) operation as the appropriate encryption (decryption) algorithm, we suggest an AQS scheme based on teleportation of quantum walks with two coins on a four-vertex cycle, which is used to transfer the message copy from the sender to the receiver. In light of the model of teleportation of quantum walks, the sender encodes the message to be signed into her or his coin state, and the necessary entangled states can be created as a result of the conditional shift between the coin state and the position state. The measurements performed on the generated entangled states are the bases of signature production and message recovery. Then according to the classical measurement results from the sender, the receiver performs the appropriate local unitary operations (i.e., Pauli operations) on his own coin state to recover the original message and further verifies the validity of the completed signature by using the appropriate verification algorithms under the aid of the trustworthy arbitrator. The suggested AQS scheme makes the following contributions: 1) the necessary entangled states for quantum teleportation of message copy do not need preparing in advance, and they can be produced automatically by the first step of quantum walks; 2) the scheme satisfies the features of non-repudiation, un-forgeability and non-disavowal due to the use of the KCCC operation; 3) the scheme may be achieved by linear optical elements such as beam splitters, wave plates, etc., because quantum walks have proven to be realizable in different physical systems and experiments.Analysis and discussion show that the proposed AQS scheme possesses the impossibility of disavowals by the signer and the receiver and impossibility of forgeries by anyone. Comparisons reveal that the designed AQS protocol is favorable. Furthermore, it provides an idea by employing the quantum computing model into quantum communication protocols with a possible improvement with respect to its favorable properties, for example, the automatic generation of entangled states via the first step of quantum walks on different models. In the near future, we will further investigate the production of entanglement by quantum walks and its applications with some improvements in designing the quantum communication protocols. Keywords:quantum cryptography/ arbitrated quantum signature/ quantum walk-based teleportation/ key-controlled chained CNOT operation
${P_{{\rm{disavowal}}}}(m) = \left( {\begin{array}{*{5}{c}} n \\ m \end{array}} \right){\left( {\frac{1}{2}} \right)^m}{\left( {\frac{1}{2}} \right)^{n - m}}, $
其中
$\left( {\begin{array}{*{20}{c}} n \\ m \end{array}} \right) = \frac{{n!}}{{m!(n - m)!}}.$
如图4所示, 图中呈现了$n = 50,100,150$三种情况, 横轴表示被抵赖的量子比特数m, 纵轴为Alice抵赖m个量子比特的概率${P_{{\rm{disavowal}}}}(m)$, 可以发现随着n值变大, 抵赖概率的最大值在变小, 可以推断当n非常大时, Alice抵赖的概率可以非常小或接近0. 这时假定抵赖概率阈值为${P_{{\rm{threshold}}}}$, 我们规定如果${P_{{\rm{disavowal}}}}(m)$小于${P_{{\rm{threshold}}}}$, 认为不存在抵赖行为, 否则认为有抵赖行为存在. 当n是确定的, 抵赖概率阈值可以选择为抵赖概率的平均值, 即${P_{{\rm{threshold}}}} = {{\sum\limits_m {{P_{{\rm{disavowal}}}}(m)} }/n}$. 图 4n = 50, 100, 150三种情况下Alice成功抵赖签名的概率${P_{{\rm{disavowal}}}}(m)$ Figure4. Alice’s disavowal probability ${P_{{\rm{disavowal}}}}(m)$ as a function of the amount m of the disavowed qubit in the signature state $|{S_a}\rangle $ for the respective $n = 50$, $n = 100$ and $n = 150$.