MD5 is the abbreviation of message-digest algorithm 5 (message-digest algorithm). It is widely used in encryption and decryption technology. It can be said to be the "digital fingerprint" of a file. Any file, whether it is an executable program, an image file, a temporary file or any other type of file, regardless of its size, has and has only one unique MD5 information value, and if the file has been modified, its MD5 The value will also change accordingly. Therefore, we can verify whether the file has been "tampered with" by comparing the MD5 value of the same file.

The role of MD5:

When we download a software, if we want to know whether the downloaded software is exactly the same as the original file of the website, we can make a MD5 checksum. If the MD5 value obtained is the same as that published on the website, it can be confirmed that the downloaded file is complete. If there is a difference, it means that the file you downloaded is incomplete: either an error occurred during the network download process, or the file has been modified by someone else. To prevent others from inserting viruses when they change the file, it is best not to use it.

When we send a file to a friend by e-mail, we can tell the other party the MD5 value of the file to be sent, so that the friend can verify it after receiving the file to determine whether the file is safe.

Another example: after just installing the system, you can perform an MD5 check on the system files. After a period of time, if you suspect that some files have been replaced, you can verify the Do an MD5 check on the file. If it is different from the MD5 check code obtained before, then there is definitely something wrong.

Read and verify MD5 information:

After understanding the MD5 information, let's take a look at how to read and verify the MD5 information of the file. This requires a special small software to detect MD5 values ??- Windows MD5 Check (download address: 2.onlinedown.net/down/WinMD5.rar, version 2.0 Build 0123). This is a green software, just decompress it and run the MD5.EXE file. The use of the software is very simple. Click the "Open" button, select and open the file you want to verify. After a moment, the MD5 value of the file will be displayed in the MD5 column. Compare this value with the value published on the website. Compare to determine whether the file is complete. Click the "Save" button to save the read MD5 as an .MD5 file. Open the file with Notepad and copy the MD5 value.

In order to verify whether the MD5 value of the file has changed after modification, a text file may be used for testing. The first file is the original file for testing, the second file is the modified file (but only a space is added after opening the original file), and the third file is a copy of the original file. Although the changes are not major, the MD5 values ??of the two files are quite different, while the copied files will not change.