Cryptography includes symmetric encryption, asymmetric encryption, hash function, digital signature and cryptographic hash function.

1, symmetric encryption

This encryption method uses the same key for encryption and decryption. In other words, the sender and the receiver need to use the same key to encrypt and decrypt information. Common symmetric encryption algorithms are AES (Advanced Encryption Standard) and DES (Data Encryption Standard).

2. Asymmetric encryption

Asymmetric encryption uses two keys: a public key and a private key. The public key is used to encrypt information and the private key is used to decrypt information. This encryption method allows anyone to encrypt information with the public key, but only those who have the private key can decrypt the information. Common asymmetric encryption algorithms are RSA(Rivest-Shamir-Adleman) and ECC (Elliptic Curve Cryptography).

3. Hash function

Hash function converts input of arbitrary length into output of fixed length. The hash function is one-way, which means that the input cannot be recovered from the output. Hash function is mainly used to store passwords, because even if someone gets the hash value, it is not easy to get the original password.

4. Digital signature

A digital signature uses a private key to sign information and a public key to verify the signature. This can ensure that the information has not been tampered with during transmission and was sent by a specific sender.

5, encryption hash function

This is a special hash function used to generate a fixed-length digest (also known as a "fingerprint"). It is used to verify the integrity and authenticity of data, especially in data integrity check, digital timestamp, digital watermark and data compression.

The above contents refer to Baidu Encyclopedia-Cryptography Technology.