The article "The New Direction of Cryptography" is the first book to put forward the concept of public key cryptosystem.

Public key cryptosystem is the most important invention and progress of modern cryptography. Cryptography is generally understood as protecting the confidentiality of information transmission.

This is only one aspect of today's cryptography theme. Verifying the true identity of the sender and receiver of information, undeniable information sent/received afterwards and protecting data integrity are another aspect of modern cryptography.

The public key cryptosystem has solved these two problems well, and has produced many new ideas and schemes. In public key systems, encryption keys are different from decryption keys. People make the encryption key public and anyone can use it; Only the decryptor knows the decryption key. RSA is by far the most famous and widely used public key cryptosystem.

Key Pairs In a security system based on public key system, keys are generated in pairs, and each pair of keys consists of a public key and a private key. In practical application, the private key is kept by the owner himself, while the public key needs to be made public. In order to make public key system-based services (such as e-commerce) widely used, a basic key problem is the distribution and management of public keys.