MD5 Unhash

[PoojaKrishna]

Hai friends,

I have a string, ie encrypted using the MD5 algorithm.

I know the secret word that is used to encrypt.

How could I get the string decrypted.

Please help

Pooja.

[Richard Robertson]

Hash functions don't work in a round trip fashion. MD5 is a hash, not an encryption.

[PoojaKrishna]

Thank you Richard for your reply.

So, is it not possible to unhash the string using MD5.

Pooja.

[JRowe]

If you have a database of hashes, you can guesstimate correct reversals, but for any large length it's impossible. Unless you have a few supercomputers in the garage.

The only reason so reverse an MD5 is to get at passwords, usually. It is an extremely interesting mathematical pursuit, and it's theoretically possible to generate an algorithm that encompasses every possible string for a particular hash.

ae661d08d1ca1576a6efcb82b7bc502f

is the hash of

blah blah

If you have the passphrase, you can generate a list of all possible phrases that result in that hash up to length n. Since generating the phrase for length N consists of iterating through all possible combinations of characters of length N, you are dependent on a brute force method.

As an aside, finding an algorithm for any given passphrase that returns the original hashed value is part of the P vs NP problem; There are general solutions for particular values, but no solutions encompassing the entire problem domain. If I had to retrieve the hashed data, I would need to know how long it was, what type of data it consisted of, and so on, to refine the required brute force approach. Even then, if it was very large, it would take a long time to get the original data.

If a general purpose solution were found that reversed MD5 for arbitrary passphrases, which returned unhashed data of specified length, you'd have a helluva compression method, not to mention a general purpose data transmission dream.

[PoojaKrishna]

Thank you Jrowe.

[AzKay]

If you have a database of hashes, you can guesstimate correct reversals, but for any large length it's impossible.

Not impossible, Just time consuming.

[Richard Robertson]

Time consuming is putting it lightly.

[AzKay]

Time consuming is putting it lightly.

...Nonetheless xD

[torels]

Or you could use a Rainbow Table. It's an enormous database containing thousands of hashes... but it's very very heavy

I think brute force is the most appropriate method... but it will take ages for long strings