Study On Continuous Variabie Quantum Deterministic Key Distribution Protocols

Quantum cryptography is a novel one in the field of cryptography, which is generated by the combination of classical cryptography and quantum mechanics, its content mainly includes quantum key distribution (QKD), quantum secret sharing (QSS), quantum secure direct communication (QSDC), quantum encryption algorithm (QEA), quantum identification (QI), quantum signature (QS) and so on. Unlike the classical cryptography, the quantum cryptography utilizes the quantum physics attributes to protect the information. According to Heisenberg uncertainty principle and quantum no-cloning theorem, any illegal attempts to eavesdrop the information will inevitably introduce additional noise in the channel, and thus will be detected by the legal parties, this promises the quantum cryptography to be unconditional secure.Quantum key distribution is a very important topic and application of quantum cryptography, it is mainly realized through the quantum optical signal. As the single photon’s complex preparation and low channel capacity, the discrete variable quantum key distribution (DVQKD) that uses the single photons or weak laser pulses have been difficult to satisfy the communication demands nowadays. Fortunately, the continuous variable quantum states such as coherent state, squeezed state can be easily generated and operated by linear optical components, they can greatly improve the channel capacity, thus the continuous variable quantum key distribution (CVQKD) can be a good solution to the problem of instant messaging. However, the existing CVQKD protocols can only generate random keys, worse still, the sender can only send the keys to one receiver in one communication, this can neither meet the requirements of deterministic keys in real life nor exploit the full advantages of continuous variable quantum signals. Focusing on the hot subject of CVQKD, along with the techniques of QSS and QSDC, some novel continuous variable quantum deterministic key distribution protocols are proposed between two parties or multiparties. Furthermore, the security of each protocol is analyzed in detail from information theory. The main research results are as follows:In quantum key distribution, according to the principle and mechanism of deterministic key.(1) by exploiting quantum teleportation, a continuous variable quantum deterministic key distribution (CVQDKD) protocol is proposed using two-mode squeezed vacuum state and coherent state. The efficiency is100%under the homodyne detection, its security is analyzed from quantum mechanics and information theory;(2) by exploiting the entanglement properties of the continuous variable quantum GHZ state, a tripartite quantum deterministic key distribution (TQDKD) protocol is designed, in which the key is generated from its ampitude, and the phase can be used to test and verify the channel’s security. The analysis results of information theory show that, when the channel transmission efficiency is greater than0.5, the proposed protocol can securely hand over the pre-deterministic key to two receivers simultaneously, and it can also be extended to multiparty quantum deterministic key distribution when preparing multiple entangled state.In quantum secret sharing, with the essence that QSS is also a way of key distribution, a continuous variable quantum secret sharing (CVQSS) scheme is proposed by using the quantum teleportation, which can be used to send pre-deterministic keys. It utilizes the squeezed state to carry the secret and the quantum teleportation to deliver the secret, the scheme can work successfully under a low degree of squeezing. The safety analysis results show that, when the secret messages are transmitted, any individual measurements or malicious attacks can obtain nothing, the messages can only be recovered when all of the participants have an cooperation.In quantum secure direct communication, based on the entanglement properties of the two-mode squeezed state, a continuous variable quantum secure direct communication (CVQSDC) scheme is proposed, and its security analysis model is established under the ideal situation and the noise environment. The scheme requires the sender and the receiver to have an identity authentication before exchanging their message, which can effectively avoid the middle attacks. The researches show that the design scheme can not only be used to secure direct communication, but also be used to distribute pre-deterministic keys.