Study Of Secret Sharing Schemes And Dialogue Schemes Based On Quantum Theory

With the development of human society,information exchange between people becomes more urgent and frequent. How to ensure the security of the information in the exchange process gave birth to a new science, cryptography. Most conventional cryptographic algorithm widely used nowadays is based on the unproven computational assumptions. However, with the development of computer science and the breakthrough of the factoring algorithm,the information security mechanism depending on these unproven computational assumptions will face great challenge. The appearance of the quantum cryptography helps cryptographers out of this dilemma. Quantum cryptography,is the synthesis of quantum mechanics with the art of code making (Cryptography), its security is guaranteed by the fundamental laws of physics. Quantum no cloning theorem and Heisenberg’s uncertainty principle ensure the unconditional Security and the ability of detecting eavesdropper, these facts guarantee that quantum cryptography has the excellent capacity and the attractive foreground. Focusing on the frontier research subjects of quantum cryptography, the main results we obtained in the dissertation are as follows:(1) We propose a protocol for multi party quantum secret sharing utilizing four non orthogonal two particle entangled states. In the protocol, all the entangled states can be used for generating the private key except those used for eavesdropping check. The theoretic efficiency for qubits of the protocol is improved from 50% to approaching 100%. The protocol is secure against to insider participant’s attack, such as invisible photon eavesdropping attack; the delay photon Trojan horse attacker and dense coding attack. The validity of a probable attack called opaque cheat attack to this kind of protocols is considered in the paper for the first time.(2) We analyze two efficient high capacity quantum secret sharing schemes and then propose a protocol for quantum secret sharing with coding of two particle quantum entanglement states directly. In this protocol, the sharing of the secret is accomplished by coding of the two particle quantum entanglement states but not the coding of some special discrete unitary operations. The security of the proposed protocol is analyzed, the scheme has a high intrinsic efficiency for qubits and a high capacity. We give the method to generalize our QSS scheme to multiparty QSS scheme. We also discuss an awkward situation that the sharing secret information is determined by the agents but not the boss existed in some schemes available and we give a variant of our scheme to avoid this problem.(3) We analyze the security of a three party quantum secret sharing of secure direct communication based onχtype entangled states, the protocol is insecure. Applying intercept and resend attack, one agent, Bob, but not Charlie, can gain Alice’s secret without the help from the other agent, Charlie. We also give our effective modification to improve the protocol.(4) We study the security of a multiparty quantum secret sharing scheme based on Bell measurement, the protocol is not secure for any dishonest agent Alice (or Bob), who can illegally elicit half of Trent’s secret message by himself. Finally a feasible improvement of this quantum secret sharing protocol is proposed. As we just change the transformation rule, the improved protocol also has the following optimal efficiency as the original protocol: (a) All the agents need not prepare any quantum state or carry out local unitary operations. (b)When generating keys, all agents only need to perform Bell measurement no matter how many participants there are in the QSS task. (c) No classical information is required to be transmitted during the protocol except for the detection process. (d) All instances are transmitted through the quantum channel only once which means fewer particles is wasted in the channel noise.(5) We study the security of a quantum secret sharing scheme between multiparty and multiparty, the protocol is not secure for the last member in the first group can illegally obtain most secret messages without introducing any error. Finally, a possible way to avoid the security flaw is suggested.(6) We put forward an efficient quantum dialogue protocol using single photons. The protocol overcomes the information leakage problem existed in most previous quantum dialogue protocols and has a high efficiency for qubits. The protocol is secure against denial of service attack, the delay photon Trojan horse attack and invisible photon eavesdropping attack. As only single photons were used in the protocol, the protocol is experimentally feasible within current technologies.