In 1976, American scholars Dime and Henman proposed a new key exchange protocol to solve the problem of public information transmission and key management, allowing communication parties on insecure media to exchange information securely. An agreed upon key is called a "public key system". Unlike symmetric encryption algorithms, asymmetric encryption algorithms require two keys: public key and private key. The public key and the private key are a pair. If the public key is used to encrypt data, only the corresponding private key can be used to decrypt it; if the private key is used to encrypt the data, then only the corresponding public key can be used to decrypt it. Decrypt. Because encryption and decryption use two different keys, this algorithm is called an asymmetric encryption algorithm. The encryption and decryption process of data is controlled through cryptography and keys. The security of the cryptographic system depends on the security of the key. Modern cryptography does not pursue the confidentiality of the encryption algorithm, but pursues the completeness of the encryption algorithm, that is, the attacker has no way to decrypt the algorithm without knowing the key. Find a breakthrough. Depending on whether the keys used in the encryption and decryption algorithms are the same, or whether the encryption (decryption) key can be simply obtained from the encryption (decryption) key. Cryptosystems can be divided into symmetric cryptography systems and asymmetric cryptography systems. Asymmetric cryptography is also called public key encryption technology. This technology was proposed to address the shortcomings of private key cryptography (symmetric encryption algorithm). Different from the symmetric cryptosystem, in the public key encryption system, encryption and decryption are relatively independent. Two different keys are used for encryption and decryption. The encryption key (public key) is open to the public and can be used by anyone. Decryption The key (secret key) is known only to the decryptor himself, and illegal users cannot deduce the decryption key based on the public encryption key. This greatly enhances the intensity of information protection. Public key cryptography not only solves the problem of key distribution, it also provides means for signature and authentication. There are many asymmetric cryptographic algorithms, the more typical of which is the RSA algorithm. Its mathematical principle is the decomposition of large prime numbers.