Mysqli: I can't login with hashed password

Question

I'm using mysqli with hashpassword. I can't log in using my password and I don't know why. I tried all my best but its not working at all.

I'm using utf8 in my database.

This is my regiter php

<?php
if(isset($_POST["register"])){

    if(!empty($_POST['name']) && 
       !empty($_POST['studno']) &&
       !empty($_POST['password']) && 
       !empty($_POST['cpassword']) && 
       !empty($_POST['email'])) 
    {
        $name=$_POST['name'];
        $studno=$_POST['studno'];
        $password= password_hash($_POST['password'],PASSWORD_BCRYPT);
        $email=$_POST['email'];

        $con=mysqli_connect('localhost','root','') or die(mysqli_error($con));
        mysqli_select_db($con,'inventory') or die("cannot select DB");

        $query=mysqli_query($con,"SELECT * FROM users WHERE studno='".$studno."'");
        $numrows=mysqli_num_rows($query);
        if($numrows==0) {
            $sql = "INSERT INTO users(name,studno,email,password) "
                 . " VALUES('$name','$studno','$email','$password')";

            $result=mysqli_query($con,$sql);
            if ($_POST['password'] == $_POST['cpassword']) {
              if ($result) {
                  header("Location: index.php?registered=1");
              }
            } else {
               header("Location: signup.php?passwordnotmatch=1");
            }
        } else { /* numrows != 0 */
            header("Location: signup.php?alreadyinuse=1");
        }

} else {
    header("Location: signup.php?allfieldisrequired=1");
    }
}
?>

this is my log in php.

<?php
if (isset($_POST["login"])) {
    if (!empty($_POST['studno']) && !empty($_POST['password'])) {
        $studno=$_POST['studno'];
        $password=$_POST['password'];
        $con=mysqli_connect('localhost','root','') or die(mysql_error($con));
        mysqli_select_db($con,'inventory') or die("cannot select DB");
        $query=mysqli_query($con,"SELECT * FROM users WHERE studno='".$studno."' AND password='".$password."'");
        $numrows=mysqli_num_rows($query);
        if ($numrows!=0) {
            while($row=mysqli_fetch_assoc($query)) {
                $dbstudno=$row['studno'];
                $dbpassword=$row['password'];
            }
            if ($studno == $dbstudno && password_verify($dbpassword,$row['password']))) {
                session_start();
                $_SESSION['sess_user']=$studno;
                /* Redirect browser */
                header("Location: home.php");
            }
        } else {
            header("Location: index.php?error=1");
        }
    } else {
        header("Location: index.php?missing=1");
    }
}

Answer 1

A lot of people commented this already, but I shall post it as an answer:

There are quite some things wrong with your code:

1) You need to verify the user's input against the database, not the database against the database. What this means is that the following line will work:

password_verify($password,$row['password'])

2) Your SQL queries do not have anything to prevent sql injection, look it up.

3) Your registration page allows for user iteration, look it up.

4) Don't use a while loop to get only the first row of a database, just use a single mysqli_fetch_assoc and it will return the first row. Also use LIMIT 1 at the end of your query if you expect only one result.

5) When selecting from a database, always specify the columns you need returned unless you are absolutely sure you need ALL columns that are returned, this will speed up your queries a lot.

6) Create your mysqli connection globally (for instance, create a database.php file and connect to the database there) instead of creating a connection in every php file you use.

7) Start the session globally (for instance, create a user.php file where a session is created and the currently logged in user data is stored). Your registration page should check for a logged in user and so does the login page (why login or register if already logged in?) so you need to globally start the session somewhere.

Answer 2

You are verifying the same password with the same hash. Use

 password_verify($password, $dbpassowrd);

And your code is easily vulnerable to SQL Injection attacks. Validate it, sanitize user input and use prepared staments.

Answer 3

What you need to do is simple. Your code will never return results for this one reason "SELECT * FROM users WHERE studno='".$studno."' AND password='".$password."'" this will never return any results, as you have saved the password as hash when registering, now what happens, when a user log's in you are selecting the everything from the users table that that matches the where clause which is the studno and a password so this will never work as the password that comes from the user is unhashed therefor it will never match a hashed password. You need to remove the password from the where clause, and only have the id in the where clause.

Again this is wrong password_verify($dbpassword,$row['password'])) remember $dbpasssword and $row['password'] are the same thing remember you have this in your script $dbpassword=$row['password']; so basically your password_verify() is reading like this password_verify(storedHash,storedHash) You are verifying a stored hash against the same stored hash. password_verify() should always read like : password_virify(PasswordFromTheUserInput,StoredHash) you must verify the password from the user input against the stored hash.

So with that been said your script should look similar to this:

<?php
ob_start();
session_start();

//Extract the inputs from the user



$query  = ("SELECT  studno,password FROM users WHERE studno='" . $studno . "'");
$result = $con->query($query);
if ($result->num_rows > 0) {
    // we have the results
    while ($row = $result->fetch_assoc()) {

        $dbstudno   = $row['studno'];
        $dbpassword = $row['password'];

        // check user password against stored hash
        if (password_verify($password, $dbpassword)) {
            // password correct start a session

            $_SESSION['sess_user'] = $studno;
            /* Redirect browser */
            header("Location: home.php");
        } else {

            header("Location: index.php?error=1");

        }


    }
} else {
    header("Location: index.php?missing=1");
}
?>

Hope this helps, I might have missed something but the logic should be someway be identical to the above, I'm not good with mysqli, I use PDO most of my life.

NB: Please take into consideration the answer from @John Smith he made very important points that you need to apply.