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In this article, the editor introduces "what is the concept of MD5" in detail, the content is detailed, the steps are clear, and the details are handled properly. I hope this article "what is the concept of MD5" can help you solve your doubts.

MD5

MD5 message digest algorithm (English: MD5 Message-Digest Algorithm), a widely used cryptographic hash function, can produce a 128bit (16-byte) hash value (hash value) to ensure complete and consistent transmission of information. MD5 was designed by American cryptographer Ronald Linn Rivest and made public in 1992 to replace the MD4 algorithm.

Application:

Consistency verification

A typical application of MD5 is to generate a summary (Message-Digest) of a piece of information (Message) to prevent it from being tampered with. For example, under Unix, many software downloads a file with the same file name and a file extension of .md5, which usually has only one line of text, such as: [1]

MD5 (tanajiya.tar.gz) = 38b8c2c1093dd0fec383a9d9ac940515

This is the digital signature of the tanajiya.tar.gz file. MD5 treats the whole file as a large text message and produces this unique MD5 message summary through its irreversible string transformation algorithm. In order to give readers an intuitive understanding of the application of MD5, the author uses an example and an example to briefly describe its working process:

As we all know, everyone on earth has their own unique fingerprint, which is often the most reliable way for judicial organs to identify criminals; similarly, MD5 can produce an equally unique "digital fingerprint" for any document (regardless of its size, format, or number). If anyone makes any changes to the document, its MD5 value, that is, the corresponding "digital fingerprint" will change.

We often see its MD5 value in the software information of some software download sites, and its function is that after downloading the software, we can do a MD5 check on the downloaded files with special software (such as Windows MD5 Check, etc.) to ensure that the files we get are the same as those provided by the site.

Specifically, the MD5 value of the file is like the "digital fingerprint" of the file. The MD5 value of each file is different, and if anyone makes any changes to the file, the MD5 value, that is, the corresponding "digital fingerprint", will change. For example, the download server provides an MD5 value for a file in advance. After downloading the file, the user recalculates the MD5 value of the downloaded file with my algorithm. By comparing whether the two values are the same, you can judge whether the downloaded file is wrong or whether the downloaded file has been tampered with. MD5 is actually a lossy compression technology, the MD5 value of the file before compression must be the same, on the contrary, the same MD5 value does not guarantee that the data before compression is the same. The probability of this happening in cryptography is very small, so MD5 has a place in the field of password encryption. But professional hackers and even ordinary hackers can take advantage of the principle that the MD5 value is actually lossy compression technology and use the value of the inverse operation of MD5 as a hash table commonly known as the rainbow table to crack the password.

The scheme of file verification using MD5 algorithm is widely used in software download station, forum database, system file security and so on.

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