Can I create a file directly with an MD5 value?

MD5 is often used on forums and software releases, in order to ensure the correctness of the file, to prevent some people from stealing the program, adding some Trojans or tampering with the copyright, a set of verification system designed. Each file can be calculated with a fixed MD5 code using the MD5 validator. Software authors often calculate the MD5 code of their programs in advance and post them on the Internet.

Therefore, when you see a program ** next to the MD5 code on the Internet, you can write it down, ** after this program use the MD5 verification program to calculate the MD5 code of your ** file, and you have written down the MD5 code before, you will know whether you are under the original, if the two are the same, then what you are ** is the original. If the calculation does not match the one noted on the Internet, then the document of your ** is incomplete, or it has been tampered with by others.

I wrote it myself, I don't know if I made it clear.

I found some relevant information:

MD5 stands for Message-Digest Algorithm 5, which was invented in the early 90's by MIT's Computer Science Lab and RSA Data Security Inc, and developed from MD2, MD3 and MD4.

message-digest generally refers to the hash transformation of a byte string (message), that is, to convert a byte string of any length into a large integer of a certain length. Note that I used the word "byte string" instead of "string" because this transformation is only related to the value of the byte, not the character set or encoding.

MD5 converts arbitrary length of "string of bytes" into a large integer of 128 bits, and it is an irreversible string conversion algorithm, in other words, even if you see the source program and the description of the algorithm, you can't convert a value of MD5 back to the original string, mathematically speaking, because there are infinitely many original strings, which is a bit like a mathematical function with no inverse function.

A typical application of MD5 is to generate a fingerprint on a message (a string of bytes) to prevent it from being "tampered with". For example, if you write a paragraph in a file called and generate an md5 value for this and record it, then you can spread the file to someone else, and if someone changes anything in the file, you will find out when you recalculate the md5 of the file (the two md5 values are not the same). If there is a third-party certification authority, MD5 can also prevent "repudiation" by the author of the document, which is called a digital signature application.

MD5 is also widely used in encryption and decryption technology, in many operating systems, the user's password is saved in the form of MD5 value (or similar other algorithms), when the user login, the system calculates the password entered by the user as the MD5 value, and then compares it with the MD5 value saved in the system, and the system does not "know" what the user's password is.

Generally, you can't, you can try this.

Dizzy. This is a paragraph answer calculated based on the content of the document.

If the content changes.

The md5 value changes.

If it doesn't change, then MD5 certainly won't change.

This is often the way to see if a file has been corrupted.