The Security Of Practical Quantum Key Distribution Systems

Quantum communication is a new research frontier born from the union between quantum physics and information science.The principles of quantum mechanics allow quantum communication protocols to have more advantages than their classical coun-terparts.Quantum communication presently includes quantum key distribution(QKD),teleportation,quantum secret sharing,quantum digital signatures,quantum bit commit-ment,quantum fingerprinting,quantum repeaters,quantum data locking,determinis-tic secure direct communication,and so on.Heisenberg' s uncertainty principle and quantum superposition are the core of quantum communication;their unique properties have inspired intense explorations of both the theoretical foundation and experimen-tal implementations of quantum physics,and have engendered many different quantum communication protocols and schemes.Compared to other protocols,QKD has been developing for more than 30 years,and is presently a highly mature technology,on the brink of entering a practical engineering phase.For example,the construction of the Beijing-Shanghai and Shanghai-Hangzhou QKD fiber transmission trunk lines were finished in 2016.In particular,the first quantum experiment satellite“Mo Zi"(or"Micius")based on free space transmission and the space lab "Tiangong 2" to test the QKD space-ground link were both successfully launched in 2016.Different protocols of QKD have been proved by the laws of quantum mechan-ics and information theory to be secure.However,in practice,quantum cryptography itself still faces many security challenges,due to the imperfection of the devices in actual systems.Although the device-independent protocol can establish private corre-lations between two parties,and essentially block the loopholes of imperfect practical systems,its implementation requires loophole-free Bell tests and still faces many tech-nical challenges.It is now believed that measurement-device-independent QKD is the best combination of security and practicality.However,it requires a crucial assumption that the modulation encoding of both the polarization and the phase must be perfec-t.Obviously,this assumption is very impractical.Therefore,to enhance the security of quantum cryptography,it is necessary to study the security of QKD protocols and systems from the point of view of an attacker.The author' s main research during the PhD program was on measurement-device-independent QKD,counterfactual QKD,round-robin differential-phase-shift quantum communication,and quantum secret sharing.In this thesis we propose a source-flaw-independent QKD protocol based on a measurement-device-independent entanglement witness.A tight bound for collective attacks on the Holevo information between the au-thorized parties and the eavesdropper is derived,which provides security for a practical QKD system independent of source flaws.Using this method and the detector-device-independent concept,we propose a quantum secret sharing protocol that is immune against all detector side-channel attacks;a security proof that takes into consideration source flaws is presented,and long distance multi-party key distribution is shown to be theoretically feasible.In the untrusted setting,we propose two types of modified single-photon round-robin differential-phase-shift QKD.For these two modified protocols we give the secret key rate obtainable against a collective attack and a Trojan horse attack.Furthermore,we propose a round-robin differential-phase-shift quantum secret sharing protocol.Compared with its classical counterpart,its phase error rate is independent of the bit error rate,so there is no need to monitor signal disturbances.With respect to eavesdropping attacks,we have also proposed two schemes that may be applied against practical two-way counterfactual QKD systems,by which means an eavesdropper can obtain the key without introducing additional error.