Is it possible to decrypt MD5 hashes?

Question

Someone told me that he has seen software systems that:

1. retrieve MD5 encrypted passwords from other systems;
2. decrypt the encrypted passwords and

Answer 1

MD5 is a cryptographic (one-way) hash function, so there is no direct way to decode it. The entire purpose of a cryptographic hash function is that you can't undo it.

One thing you can do is a brute-force strategy, where you guess what was hashed, then hash it with the same function and see if it matches. Unless the hashed data is very easy to guess, it could take a long time though.