It's not that hard to create an encryption that can be later decrypted, but using unique keys so no one will be able to decrypt an encrypted value.
(without getting the keys and source code of the encryption, of course)
Btw, I *think* MD5() was already decrypted by someone, but I'm far from sure.
And if anyone will be able to decrypt MD5 hashes with 100% success, trust me he won't be giving it to you.