Hook into the user_change process

I have a database with user information from a another project. Now I want to link this user data with my new wordpress installation. I want, if a user is about to login and has no WordPress profile yet, but a profile is in that other database already, then wordpress needs to create a profile based on the data, that already exists in the other database.

I’m already done with the login and it works fine…

add_filter('authenticate', 'check_login', 40, 3);
function check_login($user, $username, $password) {

    $user = get_user_by( 'login', $username );  

    $hash = kbHash($password);

    if ( $user ) {

        if (!wp_check_password( $hash, $user->data->user_pass, $user->ID) ) {
            $user = NULL;
        }

    } elseif ($kbCredentials = isKanuboxUser($username)) {

        if ($kbCredentials['hash'] == $hash)) {
            $user_id = wp_create_user( $kbCredentials['username'], $kbCredentials['hash'], $kbCredentials['mail'] );
            $user = get_userdata( $user_id );
        } else {
            $user = NULL;
        }

    } else {
        $user = NULL;
    }

    return $user;
}

function kbHash($password) {
    //TODO: additional hashing from other project
    $hash = $password;
    return $hash;
}

Now, the problem is, if some user edits his password, I need to do this hashing too and update it in the original database. Are there appropriate hooks inside wordpress?

I only found this: add_action( 'profile_update', 'some_function' );

But in that function I am not able to add my hashing to the plain text password before the wp-hashing is applied.

How to solve this?