The characteristic of the irreversible encryption algorithm is that no key is required in the encryption process. After the plaintext is input, the system will directly process it into ciphertext through the encryption algorithm. This encrypted data cannot be decrypted. After the irreversible encryption algorithm is processed, the same encrypted ciphertext is obtained and re-identified by the system before it can be truly decrypted. Obviously, in this type of encryption process, the encryption is oneself, and the decryption must be oneself, and the so-called decryption is actually a re-encryption, and the applied "password" is the input plaintext. The irreversible encryption algorithm does not have the problem of key storage and distribution, and is very suitable for use in distributed network systems. However, due to the complex encryption calculation and heavy workload, it is usually only used when the amount of data is limited, such as widely used in computer systems. The password encryption in , uses an irreversible encryption algorithm.