Research On Quantum Randomness Certification And Practical Security Of Quantum Cryptography

The combination of quantum mechanics and information science has produced the quantum information science.Quantum information science studies the representation,storage,transmission,and calculation of information at the level of basic microscopic particles.Mainly include:quantum random number,quantum communication(quan-tum cryptography,quantum teleportation),quantum computing,quantum simulation,quantum metrology,and so on.Quantum random number generator(QRNG)produces random sequence based on quantum mechanics.Randomness from QRNG is truly non-reproducible and unpre-dictable,therefore QRNG is also known as true random number generator.Regardless of classic cryptography or quantum cryptography,the secure random source is the cor-nerstone of the cryptosystem.QRNG is widely used in cryptosystems because of its true randomness and high rate.However,in the case that the QRNG's practical devices are unreliable or imperfect,quantum randomness certification methods should be adopted to estimate the quantum randomness in practical QRNG.Quantum cryptography,strictly speaking Quantum Key Distribution(QKD),pro-vides a theoretically unconditionally secure method of key sharing based on the funda-mental principles of quantum mechanics.This kind of unconditional security assumes that the eavesdropper may have a very powerful capability of physical operation and computing,and can even possess quantum computer,quantum storage,and so on.How-ever,parctical QKD system faces many security challenges.Due to the gap between physical implementation and theoretical model,there are many security loopholes in the light source,detector,and codec of the practical QKD system.My research focuses on the security issues related to QRNG and QKD.On the one hand,we study how many secure true random numbers can be generated by the QRNG protocol when the devices are untrustworthy or imperfect,this part of the work focuses on the theory;on the other hand,the practical security issues of QKD system are studied and the security loopholes are verified by experiments,this part of the work focuses on the engineering.This dissertation focuses on my major research results in quantum randomness certification and practical security of QKD,which are arranged as follows:1.We study a self-testing QRNG protocol based on dimension witness,with the assumption of independent devices.It addresses the random number extraction problem in a practical prepare-and-measure scenario with uncharacterized de-vices.However,the lower bound of min-entropy as a function of dimension wit-ness is not tight in existing works.We present a tighter bound of analytic form,by introducing the Lagrangian multiplier method to closely analyze the optimization problem on average guessing probability.Through simulation,it turns out that a significantly higher random number generation rate can be achieved in practice.2.We study a QRNG protocol based on directly optimization,with the assumption of independent devices.The estimations of min-entropy given in previous works are not optimal.As a result,the performance of quantum randomness certification in practice is still severely depressed.Here,we present a novel method to esti-mate the min-entropy through developing a reduced device model and proving its equivalence to the original one.Benefitting from this counterintuitive reduction,we can solve the min-entropy estimation problem using mixed integer program-ming effectively.Furthermore,we derive an optimal bound of analytic form in the case that constraints are made up of symmetric observed probabilities.Simu-lation results show that our work gives an optimal solution in this case and brings significant performance improvement compared to previous works.3.We study the practical security of QKD system.Due to the difference between physical implementation and ideal model,the practical security of QKD system is facing a huge threat.Commercial QKD systems typically use avalanche photo-diode single photon detector(APD)for single-photon detection,which is a gated threshold single photon detector.Eve uses blinding attack to fully control the response of Bos's APDs so that she can obtain all the sharing keys without be-ing discovered by Alice and Bob.We conduct a feasibility evaluation of this blinding-based detector control method.In addition,we design and realize an ex-periment demonstration system,perfonning an intercept-resend + blinding attack on practical QKD system to prove that this attack method is valid.