Quantum computing and the security of public key cryptography
Kai Li, Pei-Gen Yan, Qing-yu Cai · Fundamental Research · 2021
Compared with electronic computers, quantum parallelism has led to a significant increase in the computing power of quantum computers.However, the computing power of quantum computers will also be limited by the laws of physics, and hence there is no doubt that the computing power of quantum computers is not unlimited.For an algorithm, we need to consider both its space complexity and time complexity.This not only requires quantum computers to achieve large-scale integration, but also requires the quantum coherence time to be sufficiently long.If either of the above two conditions is not met, the task cannot be completed.Shor's algorithm [1] reduced the computational complexity of large integer factorization to the polynomial level.This complexity is of the same order as that of the encryption and decryption for the RSA public key cryptography protocol, which leads to the insecurity of the RSA in universal quantum computing.In addition, some other quantum algorithms show different kinds of enhanced speeds for solving different problems, such as the Grover's search algorithm [2] and its improved works [ 3 , 4 ], and the HHL algorithm [5] .With the remarkable computational power of these quantum algorithms, physicists have begun to seek suitable physical systems for the implementation of quantum computing.The implementation of quantum computing includes several basic technologies, such as preparation, precise control, measurement of the physical qubits, and construction of logical qubits.At present, there are many experimental candidate quantum computing platforms, including the superconducting system [6] , trapped ions system [7] , nitrogenvacancy centers in diamonds [8] , and ultra-cold atoms [9] .Recently, Google experimentally demonstrated quantum supremacy with a superconducting quantum computer [10] , thus placing the research on quantum computing at the forefront.With the booming development of quantum computing technology, the public key cryptosystem also needs to be updated periodically.Thus, cryptographers have to constantly look for public key protocols to resist quantum computing attacks, which leads to the emergence of postquantum cryptography.It is worth noting that although the name of post-quantum cryptography contains the word 'quantum', it essentially consists of protocols of classical cryptography.The current research on post-quantum cryptography mainly includes protocols based on the following four frameworks: the protocols based on Hash function, the pro- * Corresponding author.