In the paper [], a quantum direct communication protocol is proposed which is claimed to be unconditionally secure even for the case of a noisy channel. We show that this is not the case by giving an undetectable attack scheme.
We reply to the preceding comment which focused on whether there exists a quantum privacy amplification technique for purifying the unknown single-photon states transmitted. In this Reply, we will show that quantum privacy amplification is principally possible, and a specific scheme for direct communication protocol based on single photons has been constructed and will be published elsewhere. Then the secure direct quantum communication is secure against the attack strategy in the preceeding comment by using quantum privacy amplification directly.
Quantum secure direct communication is the direct communication of secret messages without first producing a shared secret key. It may be used in some urgent circumstances. Here we propose a quantum secure direct communication protocol using single photons. The protocol uses batches of single photons prepared randomly in one of four different states. These single photons serve as a one-time pad which is used directly to encode the secret messages in one communication process. We also show that it is unconditionally secure. The protocol is feasible with present-day technique.
Recently, Sutradhar (2024) proposed a quantum cryptographic protocol for secure vehicular communication. The author claimed that the proposed protocol is unconditionally secure and can resist various well-known security attacks of outsiders or participants. However, in this comment article, we demonstrate that the proposed protocol is vulnerable to an entangle-measure attack by a dishonest participant and an outsider, and a collusion attack by dishonest participants. In addition, theoretically it cannot guarantee the unconditional security because the hash function is not a perfect one-way function.
Quantum secure direct communication is one of the important mode of quantum communication, which sends secret information through a quantum channel directly without setting up a prior key. Over the past decade, numerous protocols have been proposed, and part of them have been experimentally demonstrated. However, the strict security proof is still in suspense. Two-way protocol is seen as one of the most practical protocol, in this paper, the security of the two-way quantum secure direct communication protocol will be proved against general attacks when the noisy and lossy channel is taken into account. There are two steps included in the proof, firstly, we need to prove that the mutual information between Alice and Bob is larger than the mutual information shared between Alice and the eavesdropper when the error rate in control mode is less than the predetermined threshold. Secondly, once the error rate is lower than the threshold, one can always find out a forward error correction code to guarantee the security of information transmission.