A few years ago, Professor Wang Xiaoyun of Shandong University discovered that MD5, a hash function algorithm widely used at home and abroad, was once considered very safe. However, Professor Wang Xiaoyun discovered that MD5 "collision" can be quickly found, that is, two files can produce the same "fingerprint". This means that when you sign a contract using an electronic signature on the Internet, you may also find another contract with the same signature but completely different content.

On August 17, 2004, the ongoing International Cryptozoology Conference (Crypto’2004) in Santa Barbara, California, USA, arranged three special reports on hash functions. After the internationally renowned cryptographers Eli

Biham and Antoine Joux successively analyzed SHA-1 and gave a collision of SHA-0, Professor Wang Xiaoyun from Shandong University deciphered MD5 and HAVAL. -128,

Reports on MD4 and RIPEMD algorithms.