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Ian · Posted: Fri Mar 21, 2008 11:59 pm Post subject: [Project] MD5 Cracker

Please, Laszlo, don't come here to flame me saying that I am incorrect. If my title it dis-pleasing, please suggest another.

For the past couple of weeks, I've been wondering how to decrypt an MD5 hash. To my dismay, there wasn't one. However, I did find that you can reverse one. This is done (If I am correct in my terms) Brute-Force. I had a few of my friends help me to create a JS script that does this. You may ask, Why JavaScript? Well, it came to my attention that it would be much neater if I were to add the hash anywhere I wanted on the page.

http://dieom.hostsnake.com/exp/md5.html

It's open source, so feel free to snatch anything you want.

Edit:

I forgot to mention that the database only holds up to 3 letter combinations (Alpha Numeric (abc 123))

Edit2:
And I didn't make the MD5 encryption function, I found it somewhere.

[VxE] · Joined: 07 Oct 2006 Posts: 948

That's an interesting project because MD5 authentication is used in some (*cough* BF2 *cough*) games to identify altered resource packages.

"Cracking" MD5 might make things like punkbuster weaker at detecting resource-based game hacks (i.e. wall hack && overskins)... Very interesting indeed...
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Oberon · Joined: 18 Feb 2008 Posts: 458

Ian · Posted: Sat Mar 22, 2008 1:17 am Post subject:

Oberon, you are mistaken. It can actually crack up to:

Laszlo · Joined: 14 Feb 2005 Posts: 3959 Location: Pittsburgh

Sorry, Ian, I can’t resist…

MD5 is not encryption (not one-to-one mapping), but a hash function. It means that any length of input is transformed to a 128-bit message-digest value. You cannot reverse it, because there are infinitely many messages, which provide the same hash, and those messages cannot be distinguished from each other. What you probably meant is to find two messages with the same hash. A few years ago Prof. Wang devised a way to construct pairs of such conflicting messages at acceptable speed. However, there is no known method for finding a message providing a given digest, except brute-force search.

I would not use any scripting language for this, but machine code (compiled from optimized assembly language). They can be a hundred times faster than interpreted scripts. And what HW do you want to run it? A few hundred processor parallel machine can do the search proportionally faster, and most of us have them: in modern graphic processors. So, if you are serious about key search, learn how to program your graphic card. It can run 100,000 times faster than a JavaScript program. And coordinate the work among thousands of machines networked together.