Fu-Chen Zhu

Cryptanalysis of the Hillery-Buzek-Berthiaume quantum secret-sharing protocol

The participant attack is the most serious threat for quantum secret-sharing protocols. We present a method to analyze the security of quantum secret-sharing protocols against this kind of attack taking the scheme of Hillery, Buzek, and Berthiaume (HBB) [Phys. Rev. A 59 1829 (1999)] as an example. By distinguishing between two mixed states, we derive the necessary and sufficient conditions under which a dishonest participant can attain all the information without introducing any error, which shows that the HBB protocol is insecure against dishonest participants. It is easy to verify that the attack scheme of Karlsson, Koashi, and Imoto [Phys. Rev. A 59, 162 (1999)] is a special example of our results. To demonstrate our results further, we construct an explicit attack scheme according to the necessary and sufficient conditions. Our work completes the security analysis of the HBB protocol, and the method presented may be useful for the analysis of other similar protocols.

Comment on: “Quantum exam” [Phys. Lett. A 350 (2006) 174]

The security of quantum exam [Phys. Lett. A 350 (2006) 174] is analyzed and it is found that this protocol is secure for any eavesdropper except for the “students” who take part in the exam. Specifically, any student can steal other examinees’ solutions and then cheat in the exam. Furthermore, a possible improvement of this protocol is presented.

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

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.

Consistency of shared reference frames should be reexamined

In a recent Letter [G. Chiribella et al., Phys. Rev. Lett. 98, 120501 (2007)], four protocols were proposed to secretly transmit a reference frame. Here We point out that in these protocols an eavesdropper can change the transmitted reference frame without being detected, which means the consistency of the shared reference frames should be reexamined. The way to check the above consistency is discussed. It is shown that this problem is quite different from that in previous protocols of quantum cryptography.

CONTROLLED QUANTUM SECURE DIRECT COMMUNICATION WITH W STATE

Utilizing W state, which is much more robust than GHZ state, we propose a protocol for three-party controlled quantum secure direct communication (QSDC). The feature of this protocol is that the sender encodes the secret message directly on a sequence of particle states and faithfully transmits them to an arbitrary one of two receivers without revealing any information to a potential eavesdropper. On the other hand, we construct the efficient quantum circuit to implement the QSDC by means of primitive operations in quantum computation.

CONTROLLED QUANTUM SECURE DIRECT COMMUNICATION WITH QUANTUM ENCRYPTION

Utilizing a partially entangled GHZ state, we propose a novel controlled quantum secure direct communication (QSDC) with quantum encryption. Under the supervision and help of the third side, the sender and the receiver can securely share the private quantum entanglement keys used to encrypt and decrypt the secret message. According to the results of checking the eavesdropping on decoy photons, communicators can decide whether the quantum keys are reused in the next round. Not only will eavesdropping inevitably disturb the states of the decoy photons and be detected, but arbitrary transmission errors can also be corrected.

Quantum key distribution without alternative measurements and rotations

A quantum key distribution protocol based on entanglement swapping is proposed. Through choosing particles by twos from the sequence and performing Bell measurements, two communicators can detect eavesdropping and obtain the secure key. Because the two particles measured together are selected out randomly, we need neither alternative measurements nor rotations of the Bell states to obtain security.

Comment on 'Quantum secret sharing based on reusable Greenberger-Horne-Zeilinger states as secure carriers'

In a recent paper [S. Bagherinezhad and V. Karimipour, Phys. Rev. A 67, 044302 (2003)], a quantum secret sharing protocol based on reusable GHZ states was proposed. However, in this Comment, it is shown that this protocol is insecure if Eve employs a special strategy to attack.

On the information-splitting essence of two types of quantum key distribution protocols

Abstract With the help of a simple quantum key distribution (QKD) scheme, we discuss the relation between BB84-type protocols and two-step-type ones. It is shown that they have the same essence, that is, information splitting. The choice of an orthogonal carrier or a nonorthogonal carrier, which looks like the main difference between these two types of protocols, is not an important, even not a very explicit matter. This result is instructive for related scheme designing and security analyzing.

Comment on “Quantum key distribution for d -level systems with generalized Bell states”

In the paper published in Phys. Rev. A 65, 052331 (2002), an entanglement-based quantum key distribution protocol for