Research On Quantum Digital Signature Protocols

The security of most classical digital schemes is based on the computational complexity of the mathematical difficult problems.With the continuous progress of computing capacity and the appearance of quantum technology, currently the security of classic digital signature can be threatened seriously. In contrast, quantum digital signature (QDS)schemes offer security guaranteed by the laws of quantum mechanics, such as quantum entanglement, quantum no-cloning theorem, quantum uncertainty principle.At present, the research of QDS protocol is mainly divided into two directions, one is to design the ideal protocol under the assumptions of the mature quantum techlonogy, the other one is to design the protocol which can be realized udner the current quantum techlonogy. This paper makes a deep research on both of the two directions and proposes secure schemes respectively. The main works and creations are as follows:1.Arbitrated quantum signature protocol based on the chained CNOT operations encryption. At present, the encryption scheme used by most arbitrated quantum signature (AQS) protocols is quantum one-time pad (QOTP) which encrypts data qubit by qubit. There are many forgery and repudiaton attacks on AQS by utilizing the encryption features of quantum one-time pad.This paper constructs a new encryption scheme called the chained CNOT operations, which encrypts quantum message ensemble.Compared with the quantum one-time qad encryption algorithm, this algorithm is more simplely because there only CNOT operator is needed, so it can avoid the weaknss of the exchangeability of Pauli operators. Moreover, in the the chained CNOT operations encryption, one encrypted qubit is relevant to many message qubits and key bits, so it can resists the existing attacks on quantum one-time pad.Thus, this paper proposes an arbitrated quantum signature protocol based on the chained CNOT operations encryption.Security analysis shows that our protocol cannot be forged and repudiated.2.Arbitrator quantum digital signature without quantum comparison and quantum memory. Under the existing quantum techlonogy, the main factors which restrict the realization of QDS are long time quantum memory and quantum comparison.This paper improves the protocol proposed by Vedran Dunjko, which without quantum memory. The improved QDS need neither quantum comparison nor quantum memory, so it is easier to implement than the original protocol. Meanwhile, we redefine the security and make the definition of repudiation consistant with the definition of classical signature. Security analyses show that our protocol can’t be forged and repudiated.In particular, we analyze the collusion attack, the result show that our QDS is still secure under the collusion attack which taked by a finite numbers of recipients.Moreover, we present the relation between the key length L and the number of malicious recipient k if we want to keep the same forgery probability with single attacker.3.Quantum digital signature protocols based on the BB84 states. In quantum cryptography, the most mature technology is quantum key distribution (QKD), which is already commercially available. This paper proposes two protocols based one the BB84 states|0〉,|1〉 and|+〉,|-〉,which are widely used in QKD. The first scheme is an improvement on a recent QDS scheme. It requires neither quantum memory, nor quantum comparison. The scheme uses the same four quantum states as the BB84 protocol for quantum key distribution, and the measurement is the same as the BB84 protocol too. The second scheme based on the first scheme. It only need classical authentication, no quantum authentication is needed again. Security analysis shows that it cannot be forged and disavowed. Moreover, it can be implemented just needing to modify a little with the quantum key distribution components.