Question

I have this task that needs investigation as to why the md5 value of a file keeps changing.

Example:

1. I need to generate the diagnostic file of a certain machine.

2. After generating the file, it produces a .zip file, say, Diag.zip which contains all the information/files of that certain machine.

3. Inside Diag.zip file contain a .xls, say, Data.xls which contains all the summary of all files in that certain machine, includes, the directory of the file, file version, file size, create time and md5.

4. Then save all the information of Data.xls in database.

After a day or so, do it again back in Step 1-4.

Then when I queried all the save data of Data.xls in the database in a 2 weeks range, and it shows that almost all files in that certain machine have its md5 value changed.

The question is: Why is it that md5 value always changed every time I generated a new diagnostic files?

Answer 1

The MD5 is based on a lot of things. But I can assume filesize, filename & creationdate.
If one of those changes, the md5 hash changes. The exact same file will always return the exact same md5 hash. A new file always generates a new md5 hash.