From the perspective of information theory and cryptography, the security of two quantum dialogue protocols and a bidirectional quantum secure direct communication (QSDC) protocol was analyzed, and it was pointed out that the transmitted information would be partly leaked out in them. That is, any eavesdropper can elicit some information about the secrets from the public annunciations of the legal users. This phenomenon should have been strictly forbidden in a quantum secure communication. In fact, this problem exists in quite a few recent proposals and, therefore, it deserves more research attention in the following related study.

Revisiting the security of quantum dialogue and bidirectional quantum secure direct communication

A two-step quantum secure direct dialogue protocol using Einstein-Podolsky-Rosen (EPR) pair block is proposed. In the protocol, the dialogue messages are encoded on series of qubits and sent through a quantum channel directly. The security of the protocol is assured by its connection to the two-step quantum secure direct communication protocol, which has been proved secure. This protocol has several advantages. It is a direct communication protocol that does not require a separate classical communication for the ciphertext. It has high capacity as two bits of secret messages can be transmitted by an EPR pair. As a dialogue protocol, the two parties can speak to each other either simultaneously or sequentially.

Quantum secure direct dialogue using Einstein-Podolsky-Rosen pairs

From the perspective of information theory and cryptography, we analyze the security of two quantum dialogue protocols and a bidirectional quantum secure direct communication (QSDC) protocol, and point out that the transmitted information would be partly leaked out in them. That is, any eavesdropper can elicit some information about the secrets from the public annunciations of the legal users. This phenomenon should have been strictly forbidden in a quantum secure communication. In fact, this problem exists in quite a few recent proposals and, therefore, it deserves more research attention in the following related study.

A scheme is presented to implement bidirectional controlled quantum teleportation (QT) by using a five-qubit entangled state as a quantum channel, where Alice may transmit an arbitrary single qubit state called qubit A to Bob and at the same time, Bob may also transmit an arbitrary single qubit state called qubit B to Alice via the control of the supervisor Charlie. Based on our channel, we explicitly show how the bidirectional controlled QT protocol works. By using this bidirectional controlled teleportation, espcially, a bidirectional controlled quantum secure direct communication (QSDC) protocol, i.e., the so-called controlled quantum dialogue, is further investigated. Under the situation of insuring the security of the quantum channel, Alice (Bob) encodes a secret message directly on a sequence of qubit states and transmits them to Bob (Alice) supervised by Charlie. Especially, the qubits carrying the secret message do not need to be transmitted in quantum channel. At last, we show this QSDC scheme may be determinate and secure.

Bidirectional controlled quantum teleportation and secure direct communication using five-qubit entangled state

A theoretical scheme of quantum secure communication using a class of three-particle W states is proposed. In the scheme, two communicators may communicate after they test the security of the quantum channel. The receiver can obtain the secret message determinately if the quantum channel is safe. The present scheme can be realized without using teleportation.

https://iopscience.iop.org/article/10.1088/0253-6102/50/2/15/pdf

Quantum Secure Communication Using a Class of Three-Particle W State

Two protocols of quantum direct communication with authentication [Phys. Rev. A 73, 042305 (2006)] were recently proposed by Lee, Lim, and Yang. In this paper we will show that in the two protocols the authenticator Trent should be prevented from knowing the secret message. The first protocol can be eavesdropped on by Trent using the intercept-measure-resend attack, while the second protocol can be eavesdropped on by Trent using a simple single-qubit measurement. To fix these leaks, we revise the original versions of the protocols by using the Pauli $Z$ operation ${\ensuremath{\sigma}}_{z}$ instead of the original bit-flip operation $X$. As a consequence, the attacks we present can be prevented and accordingly the protocol securities are improved.

/pdf/comment-on-quantum-direct-communication-with-authentication-4uen67v3jz.pdf

Comment on : Quantum direct communication with authentication

Taking advantage of our improved gates as well as the Giorgi-Pasquale-Paganelli (GPP) nondestructive gate [Phys. Rev. A 70 (2004) 022319], the sign of any term of the initial state in the GPP model can be flipped. The success possibility of the sign Hip of odd number of terms is probabilistic (1/4), while the success possibility of the sign flip of even number of terms is deterministic (1).

Shou-hua Shi

Papers

Comment on : Quantum direct communication with authentication

Sign Flip in Giorgi–Pasquale–Paganelli Model