Protocol And Practical Security Of Quantum Cryptography

Secure communication has a deep correlation to national security,it has importan-t application for each country,government department,industry,and even everyone’s life.The modern cryptography can be divided into two categories,symmetric and asym-metric system(public-key system).Since the eighties of the last century,the present of quantum computer of quantum algorithms lead to fatal challenge to the modern crypto-graphic system.Claude Elwood Shannon proved the one-time-pad cryptography system has unconditional security,in the case of the legal parties Alice and Bob have uncondi-tional secure key,length of which is equal to the plaintext,and the secure key can not be reused.Quantum cryptography,which can also be called quantum key distribution,pro-vide unconditional key distribution.The security of quantum cryptography is protected by the uncertainty principle,quantum non-cloning theorem and quantum measurement theory.The eavesdropper can not get the key information,even if she has unlimited computation power and storage capacity.Based on the quantum key distribution and one-time-pad algorithm,the legal parties can apply secure communication.Quantum key distribution is the most mature technology of quantum information science.Physicist pay much attention to security of the protocol in the early time,now most of protocols have been proved security under the coherent attack.However,quan-tum cryptography system has much weakness in practical applications.For example,the practical source is weak coherent source,which can generate the multi photons.The phase modulator has attenuation and deviation property,the detector can be attacked under the bright light pulse.All of the imperfections can weak security of the practical system.This dissertation is the collection of the major scientific results of security of quan-tum key distribution,the major results are outlined as follow:1.Based on the quantum nonlocal correlation with quantum dimension witness,we propose the semi-device independent quantum random number expansion protocol,randomness of which is only based on the device ’s dimension.We proved the deep cor-relation between device independent protocol and semi-device independent protocol.The biased measurement outcome has also been analyzed in the semi-device indepen-dent protocol.2.The realistic beam splitter has wavelength dependent property,the coupling ratio of which varies periodically with wavelength changes.Based on this fatal security loophole,we propose wavelength-dependent attacking model.The eavesdropper can control Bob’s measurement basis with different wave length sources,and the experiment has been demonstrated correspondingly.3.The practical phase modulator has attenuation,which introduce unbalanced state preparation,the imperfection can not be analyzed with the previous analysis model.Based on the entanglement distillation and purification model,we propose the virtual equivalent source model to prove system security,and get the final key rate formula.4.Practical optical and electronic device may have imperfect operation,which can not be controlled by the eavesdropper.Based on this imperfection,we propose imperfect phase modulation model,and get the result that the imperfection can also decrease eavesdropper’s information.5.In the aspect of security of quantum key distribution protocol,the distributed-phase-reference variable protocols have higher communication efficiency and simpler equipment.Based on the continuity of the entropy,we analyzed lower bounds for the security of distributed-phase-reference variable protocol against one-pulse-attack.6.The main security of decoy state protocol is based on infinite resources case,but the practical system has finite operation time,thus only finite resources can be transmit-ted in practical case.We analyzed the relative statistical fluctuations of the yield and error rate,then proved security of the decoy state quantum key distribution with finite resources.