An overview of the current state of the problem of building a quantum computer and its hypothetical use for breaking cryptographic protocols is presented. The necessary parameters are considered. An overview of existing quantum algorithms and post-quantum cryptographic protocols that are strong with respect to them is presented. The problem of constructing a quantum computer is considered in comparison with the development of the theory and practice of conventional mechanical and electronic computers. The results of contests on the topic of post-quantum cryptography are presented.