Summary - Security

Build a secure login form with password_hash, htmlspecialchars and CSRF.

Summary - Security tools

In this group you learned four key security tools. With password_hash you store passwords safely; with password_verify you validate them. htmlspecialchars prevents XSS and prepare prevents SQL injection.

CSRF tokens block forged form submissions; you verify them with hash_equals against timing attacks. Now let us combine these tools into a secure login check.

Exercise Write a secure login check

Define a verifyLogin($password, $csrf, $hash) function. Inside it, verify the CSRF token with hash_equals($_SESSION['csrf_token'], $csrf); return false if it does not match. Then verify the password with password_verify($password, $hash). $hash and $_SESSION['csrf_token'] are already defined. Call verifyLogin with the correct password and the correct CSRF; print the result as "valid" or "invalid".

Show example solution

"invalid") . "\n";.
Example solution:
<?php
session_start();
$_SESSION['csrf_token'] = bin2hex(random_bytes(16));
$storedHash = password_hash("gizli123", PASSWORD_DEFAULT);
function verifyLogin($password, $csrf, $hash) {
    if (!hash_equals($_SESSION['csrf_token'], $csrf)) {
        return false;
    }
    return password_verify($password, $hash);
}
$ok = verifyLogin("gizli123", $_SESSION['csrf_token'], $storedHash);
echo ($ok ? "valid" : "invalid") . "\n";

Test yourself

What is the safe way to store passwords in the database?
- As plain text
- Hashed with md5
- password_hash + PASSWORD_DEFAULT
- With base64_encode
Show answer

password_hash + PASSWORD_DEFAULT — Correct. password_hash + PASSWORD_DEFAULT is the safe, modern choice.

Print the username safely

echo ____($username, ENT_QUOTES, "UTF-8") . "
";

Show answer

echo htmlspecialchars($username, ENT_QUOTES, "UTF-8") . "
";

Match each defense to its attack

password_hash

Against password leak
htmlspecialchars

Against XSS attack
hash_equals

Against CSRF forgery
prepare

Against SQL injection

Next lesson: The middleware pattern

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