database - PHP dehashing the password

Question

Ok. thats clear that one must store hashed password in the database but in case a user does not remembers the password and want to retrieve it back, then obviously the user wont like to have the hashed password. If the password is hashed with md5 or additional like salt and sha1 then how to retrieve back the password.

Answer 1

There is but one simple answer: You cannot.

Well, theoretically you could, but it could take many years per password if they are long enough. After all, that is the point of hashing passwords in the first place: to make the data effectively useless to an attacker (or at least protect the user's plaintext password, which is sensitive data.)

Just have the site send a "change your password" email containing a link to a page where that user can change his/her password. This is how most professional sites handle this dilemma.