Classical communications are used in the post-processing procedure of quantum key distribution. Since the security of quantum key distribution is based on the principles of quantum mechanics, intuitively, the secret key can only be derived from the quantum states. We find that classical communications are incorrectly used in the so-called quantum dialogue type protocols. In these protocols, public communications are used to transmit secret messages. Our calculations show that half of Alice's and Bob's secret message is leaked through the classical channel. By applying the Holevo bound, we can see that the quantum efficiency claimed in the quantum dialogue type of protocols is not achievable.
Classical communications are used in the post-processing procedure of quantum key distribution. Since the security of quantum key distribution is based on the principles of quantum mechanics, intuitively, the secret key can only be derived from the quantum states. We find that classical communications are incorrectly used in the so-called quantum dialogue type protocols. In these protocols, public communications are used to transmit secret messages. Our calculations show that half of Alice's and Bob's secret message is leaked through the classical channel. By applying the Holevo bound, we can see that the quantum efficiency claimed in the quantum dialogue type of protocols is not achievable.
We have now seen in Chapters 20–22 how Alice can communicate classical or quantum information to Bob, perhaps even with the help of shared entanglement. One might argue that these communication tasks are the most fundamental tasks in quantum Shannon theory, given that they have furthered our understanding of the nature of information transmission over quantum channels. However, when discussing the communication of classical information, we made no stipulation as to whether this classical information should be public, so that any third party might have partial or full access to it, or private, so that no third party has access. This chapter establishes the private classical capacity theorem, which gives the maximum rate at which Alice can communicate classical information privately to Bob without anyone else in the universe knowing what she sent to him. A variation of the information-processing task corresponding to this theorem was one of the earliest studied in quantum information theory, with the Bennett– Brassard-84 quantum key distribution protocol being the first proposed protocol for exploiting quantum mechanics to establish a shared secret key between two parties. The private classical capacity theorem is important for quantum key distribution because it establishes the maximum rate at which two parties can generate a shared secret key. Another equally important, but less obvious utility of private classical communication is in establishing a protocol for quantum communication at the coherent information rate. Section 22.2 demonstrated a somewhat roundabout way of arriving at the conclusion that it is possible to communicate quantum information reliably at the coherent information rate—recall that we “coherified” the entanglement-assisted classical capacity theorem and then exploited the coherent communication identity and catalytic use of entanglement. Establishing achievability of the coherent information rate via private classical coding is another way of arriving at the same result, with the added benefit that the resulting protocol does not require the catalytic use of entanglement. The intuition for quantum communication via privacy arises from the nocloning theorem. Suppose that Alice is able to communicate private classical messages to Bob, so that the channel's environment (Eve) is not able to distinguish which message Alice is transmitting to Bob.
Quantum cryptography provides secret communication, which offers various security factors like confidentiality, integrity, and authentication assurance based on the law of physics. The law of physics states that quantum computing can also be applied into the communication sector, which is particularly in the field of cryptography. Then quantum can significantly distribute the data securely by applying quantum key distribution (QKD), quantum key sharing, etc. In the classical cryptography, it is difficult to compute secret keys using security concepts like key exchange and authentication, etc., and it fails to provide adequate protection during data communication as it needs some effective computation in terms of security. The lack of security in the data communication can be overcome by using the concept of quantum computing. Generally, in quantum computing, elementary quantum systems like polarized photons are used to transmit digital information based on the principle of uncertainty as it gives rise to a significant phenomenon of effective security in terms of communication compared to existing concepts related to cryptography. In quantum computing, the detection ratio for identifying the data which are sent through a communication channel is more difficult as it uses qubits and photons to represent the data that are sent. Quantum channels are used to distribute the information between two users as it passes through the unprotected classical channels as it is unknown to anyone else. Assuming that Alice and Bob use a latent noise channel to send a key, reconciliation is the process of correcting errors between Alice and Bob’s version of the key. This is done by public discussion, which leaks some information about the secret key to an undercover. This chapter gives a discussion on QKD concepts as it helps to provide a secure communication, where the information is broadcasting through a quantum channel. Finally, the various existing quantum protocols are described in relation to some security measures based on QKD, and the standard QKD protocol of BB84 is discussed.
After carrying out a protocol for quantum key agreement over a noisy quantum channel, the parties Alice and Bob must process the raw key in order to end up with identical keys about which the adversary has virtually no information. In principle, both classical and quantum protocols can be used for this processing. It is a natural question which type of protocols is more powerful. We prove for general states but under the assumption of incoherent eavesdropping that Alice and Bob share some so-called intrinsic information in their classical random variables, resulting from optimal measurements, if and only if the parties' quantum systems are entangled. In addition, we provide evidence that the potentials of classical and of quantum protocols are equal in every situation. Consequently, many techniques and results from quantum information theory directly apply to problems in classical information theory, and vice versa. For instance, it was previously believed that two parties can carry out unconditionally secure key agreement as long as they share some intrinsic information in the adversary's view. The analysis of this purely classical problem from the quantum information-theoretic viewpoint shows that this is true in the binary case, but false in general. More explicitly, bound entanglement, i.e., entanglement that cannot be purified by any quantum protocol, has a classical counterpart. This "bound intrinsic information" cannot be distilled to a secret key by any classical protocol. As another application we propose a measure for entanglement based on classical information-theoretic quantities.
Abstract Quantum dialogue enables two communicators to send their own secret information to each other, but most of the current quantum dialogue protocols have high requirements for the hardware equipment and capabilities of the communicators. In order to reduce the cost of participant, a semi-quantum dialogue scheme based on hyperentangled Bell states is studied in this paper. In our protocol, we combines the idea of semi-quantum key distribution and semi-quantum secure direct communication to realize the exchange of secret information between Alice and Bob, Alice’s information is transmitted to Bob through semi-quantum secure direct communication, while Bob’s message is extracted by Alice through semi-quantum key distribution and one-time pad encryption. This is different from the previous semi-quantum dialogue protocols, and is a new way of thinking. The security analysis shows that our protocol can not only resist the conventional attack strategies, but also has not the drawback of ‘information leakage’ problem. Compared with the existing semi-quantum dialogue protocols, it has some advantages, such as high communication efficiency, saving classical participant’s consumption and security. Although this protocol requires the preparation and analysis of hyperentangled Bell state, which are slightly more complex, it will be shown that all these are achievable by current technology. Our protocol is fully implementable, so it has good application prospects.
Quantum key distribution (QKD) is considered as an ideal method to make secret message unreadable to eaves-dropper but intelligible to the two authorized parties of the communication [1][2][3][4][5][6].In the research of experimental quantum key distribution, single photons and entangled photon pairs are used as the carriers.In quantum key distribution, secret keys are generated first between the communication parties.The security of quantum key distribution is guaranteed by the laws of quantum mechanics.After the quantum key distribution is completed, the communication parties should share secret keys, then the sender encrypts the secret message using the secret keys to form the ciphertext and transmits the ciphertext through a classical channel.The receiver receives the ciphertext and then decrypt the ciphertext to get the secret message.Altogether there are four steps in a secret communication process with QKD: key generation, encryption, transmission and decryption.Here in this review, we review some new development in quantum communication, quantum direct communication (QDC).Quantum direct communication is a form of quantum communication where secret messages can be transmitted through a quantum channel with or without additional classical communications.There are two forms of quantum direct communication, quantum secure direct communication (QSDC) [7{9] and deterministic secure quantum communication (DSQC) [10,11].In QSDC, secret messages are transmitted directly between the communication parties, from sender Alice to receiver Bob, without additional classical communication except those for the necessary eavesdropping check.In other words, the quantum key distribution process and the classical communication of ciphertext are condensed into one single quantum communication procedure in QSDC.Deterministic secure quantum communication is another type of quantum direct communication, such as those proposed in Ref. [10,11], where classical communication is required in order to read out the secret message.As mentioned earlier, to complete a secure communication with the help of QKD, one usually encodes the secret message with an encryption scheme, and the ciphered text is transmitted through a classical channel.With a quantum channel, this procedure can be varied.