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[ANETGames]

Hello,
I'm an antivirus developer,
I'm no expert in MD5 or SHA1, but could it be possible to recreate a file from a given MD5 hash? of course it would require mass amounts of CPU, but I think it could be done.

If I made a program that would ask the user for an MD5 Hash and would then generate a file, here's the ideas:
- Open a blank file tmp.txt
- write position[x,y] where x is the file position, and y is the ord 0-255.
- Ok, so lets say the file only contains the text: a
- The program then would check the new hash, and if it matched the given hash, it would then say it found it, otherwise it'd continue.
- Then it would try just 'b', then 'c', then 'd', etc...
- once it got through the first position, if it failed to re-create the file, it can move on to the the next position, repeating the process liek so in the file:
aa
ab
ac ... zz
- Again, repeating itself multiple times until regenerating a file.
- Of course, even with Dual-Core processors or Quad, you could probably only re-create files of 500 Bytes or less.

Any thoughts on this theory?
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[Guy Deschênes]

Hi and welcome!

Well the thoughts on the issue is not new and perhaps theoretically feasible but rather impractical since as you said the processing power required would be unconventional to say the least and the possible returned output would still remain within a range of probabilities almost impossible to correlate accurately. Personally I don't think it is possible.

The MD5 is not a reversible encryption algorithm as such as it is a mathematical quantification of the overall file set and not of the internal machine instructions. It is meant primarily as a correlation mechanism such as file time & date for example. Meaning it is not designed as an encrypted version of the code itself but as an encrypted quantification of its attributes only. Nonetheless it does make it rather useful in monitoring file modifications...

While I am not an expert in cryptography I think this is the best and most accurate explanation I can provide...
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