I know that the hash value inevitably changes when the file is changed, but I am wondering how to avoid this method of changing the hash value and damage the header of the mp4 file so that it cannot be played.

CodePudding user response：

This is called a Second Preimage Attack and unless the hash algorithm is severely compromised, this is exactly one of the kinds of attacks that (cryptographic) hash algorithms are explicitly designed to prevent.

In fact, Preimage Attacks are so hard, and cryptographic hash algorithms are so secure against them that even cryptographic hash algorithms which are considered compromised such as MD5 and SHA-1 have no known practical Preimage Attacks, and never had a successful Preimage Attack mounted against them.

What you are trying to do is even harder than a simple Second Preimage Attack. A Second Preimage Attack tries to find any arbitrary input that has the same hash value as a given input. However, in your case, you are not looking for any arbitrary input but an input with a specific structure. This is even harder. In fact, such an input may not even exist at all.