Abstract: Cryptography has gone through the stages of classical cryptography, modern cryptography, and quantum key distribution. The successful launching of the first quantum satellite "Mozi" is now leading quantum key distribution onto a new journey. We present a review of the development of cryptography, with a detailed discussion of RSA public key cryptography. We also explain the Bennett―Brassard and Ekert protocols which are used in quantum key distribution. Then we describe the development of quantum communication, as well as the experimental tasks and significance of the Mozi satellite.