B. Reiter B. Reiter - 1 year ago 259
MySQL Question

Dovecot SHA512-Crypt and PHP

I've used the following instructions to install a mail server:

Now I'm trying to program a login form in PHP but don't know how to compare the entered password with the saved password.

This is the mysql-code for the password encryption:


I don't understand how it works because with every call of this function a completely new string is being generated.

This is what I have so far:

crypt($_POST[‘password’], '$6$'.substr(sha1(rand()), 0, 16))

But as I said every time I get a new string.

Answer Source

Use the PHP functions password_hash and password_verify. These functions salt and iterate to provide secure protection.

See PHP Manual password_hash and password-verify.

string password_hash ( string $password , integer $algo [, array $options ] )

Returns the hashed password, or FALSE on failure.

boolean password_verify ( string $password , string $hash )

Returns TRUE if the password and hash match, or FALSE otherwise.

Example code:

$hash = password_hash("rasmuslerdorf", PASSWORD_DEFAULT)

if (password_verify('rasmuslerdorf', $hash)) {
    echo 'Password is valid!';
} else {
    echo 'Invalid password.';

In your case you grab the password hash for that username from the database, and keep it in a variable called $hash. Then you use password_verify() like this:

password_verify($_POST["password"], $hash)

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