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At present, most of information resources are on computer's memory, and computers communicate with each other via computer networks. Those communication channels are insecure in the sense that, when a sender A sends a message to receiver B, an enemy could receive the message physically. The most important role of a cryptosystem is to make the enemy unable to know the content of the message - to guarantee the Secrety and the Authenticity of information. The cryptosystems based on symmetric algorithms use the same key for both encryption and decryption process, so the key must be kept secret. A sender and a receiver have to agree about the secret key before communication or have to use a secure channel to send secret key from the sender to the receiver. It is a matter of fact that it is not always possible. The cryptosystems based on asymmetric algorithms use one key - KB for encryption and another key - kB for decryption. A Key generator generates a pair (KB, kB) basing on the initial conditions. When B wants to send A a message, he/she uses Key generator to generate a pair (KB, kB) then sends KB (it is called Public-Key) to A, so A can use it to encrypt the message. When receiving encrypted message, B uses the secret key kB to decrypt it. The asymmetric cryptosystems must guarantee that, if the enemy receives the encrypted message and the key KB associated with it, it is not practically possible for him to calculate the secret key kB to decrypt the message. In other word, that is an intractable problem for him. The name Public-Key comes from that sense.
Hội nghị Khoa học Trường Đại học Khoa học Tự nhiên, ĐHQGHN
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Information Technology (IT)