Cryptography can be divided into several categories, and the characteristics of each are as follows:

Cryptography (Cryptography) can generally be divided into classical cryptography and modern cryptography.

Among them, classical cryptography exists as a practical art. Its encoding and deciphering usually rely on the creativity and skills of designers and opponents, and there is no clear definition of the original cryptography. Classical cryptography mainly includes the following aspects: Monoalphabetic Cipher, Polyalphabetic Cipher, and strange encryption methods.

Modern cryptography originated from a large number of related theories that emerged in the mid-to-late 20th century. In 1949, Shannon published a classic paper entitled "Communication Theory of Secrecy Systems", which marked the beginning of modern cryptography.

Modern cryptography mainly includes the following aspects: Symmetric Cryptography, represented by DES, AES, and RC4. Asymmetric Cryptography, represented by RSA, ElGamal, and elliptic curve encryption. Hash function, represented by MD5, SHA-1, SHA-512, etc. Digital signature, represented by RSA signature, ElGamal signature, and DSA signature.