MySQL ENCRYPT密码但是如何解密？

Question

I am going through this tutorial and I am using the ENCRYPT MySQL function.

http://www.pixelinx.com/2010/10/creating-a-mail-server-on-ubuntu-using-postfix-courier-ssltls-spamassassin-clamav-and-amavis/

But now I have the problem of how to decrypt the encrypted password in MySQL or in php? I want to compare if the password entered is the same as the encrypted one.

How can I compare it? MySQL must be encrypted with the ENCRYPT function!

I am searching but I can not find anything how to decrypt the ENCRYPT MySQL function...

Answer 1

ENCRYPT is using a one way hash algorithm there is no DECRYPT .. That's the sense of enrypting passwords: a hacker should have no option to see the clear text passwords.

When you need to compare a password in db with one a user has entered, use a query like this (using prepared queries)

SELECT * FROM `user`
WHERE `name` = 'hek2mgl` 
  AND `password` = ENCRYPT('user_input', `password`)

The ENCRYPT function will output a "salted" string prefixed with the salt itself, so feeding it back the encrypted password will re-supply the original salt.

Answer 2

You can't decrypt the password - it is encrypted with one-way encryption.

What you need to do is encrypt the entered password and compare the result with the stored encrypted password.

Answer 3

you don't need to DECRYPT the password. In order to check if a user submitted the correct password, just RE-ENCRYPT the password given by the user and check if it matches the one stored in your database.

Moreoever, a simple hash function will suffice (avoid MD5 and make use of salt to prevent dictionary or rainbow-tables attacks!)