AES adopts block cipher system. Firstly, the plaintext is divided into byte segments based on the length of 16 bytes. If the length is less than 16 bytes, padding is also used. Then each byte segment is encrypted in groups to obtain ciphertext, and then the final ciphertext is spliced together to form the final ciphertext. The key length of AES algorithm can be divided into 128 bits, 256 bits and 5 12 bits.

The whole encryption process is shown in the following figure:

Function realization: plaintext is encrypted by AES at the client, sent to another client through TCP link, and decrypted by key at the other end to get plaintext.