MD5 is a destructive encryption, which means it cannot be directly decrypted from the ciphertext.

The detailed description is as follows:

MD5 is an algorithm that inputs a message of variable length and outputs a fixed length of 128-bits. Through the program flow, four 32-bit data are generated, and finally combined into a 128-bits hash. The basic methods are to find the remainder, take the remainder, adjust the length, and perform loop operations with connected variables. Get results. Typically a 128-bit MD5 hash is represented as a 32-bit hexadecimal digit. The following is an MD5 hash of a 43-bit long ASCII alphabet:

MD5("The quick brown fox jumps over the lazy dog") = 9e107d9d372bb6826bd81d3542a419d6

Even if a small Changes (such as replacing d with c) will also change the hash dramatically:

MD5("The quick brown fox jumps over the lazy cog") = 1055d3e698d289f2af8663725127bd4b

And the empty text The hash of With the improvement of computer computing power, it is possible to find "collision". Therefore, MD5 is not used in situations with high security requirements.

In 2004, Wang Xiaoyun proved that the MD5 digital signature algorithm can produce collisions.

In 2007, Marc Stevens, Arjen K. Lenstra and Benne de Weger further pointed out that the MD5 algorithm can be attacked repeatedly by forging software signatures. The researchers used the chosen-prefix collision method to include malicious programs in the front end of the program, and used the space behind to add junk code to create the same MD5 hash value.

In 2007, scientists from the Eindhoven University of Technology in the Netherlands successfully performed an MD5 collision between two execution files, so that the two programs with different execution results calculated the same MD5.

In December 2008, a group of researchers successfully generated a forged SSL certificate through MD5 collision, which allowed the server to forge the signatures of some root CAs in the https protocol.