Introduction:

Passwords are the keys to our online lives, safeguarding our data and personal information. It is crucial to store passwords securely to prevent unauthorized access. One common practice to ensure password security is to store hashed versions of passwords, rather than the passwords themselves. Hashing is a one-way process that converts a password into an irreversible string of characters.

But what happens when you need to convert a hashed password back to its original form? Perhaps you've forgotten a password, or you're working on a system migration. In this blog, we will explore various methods to reverse a hashed password back to its original string using PHP.

Method 1: Brute Force Attack

Brute force is the most basic and least efficient method to reverse a hashed password. In a brute force attack, you try every possible combination of characters until you find a match with the hashed password. This method is extremely time-consuming and resource-intensive, especially for strong passwords.

Let's create a simple PHP program to demonstrate this method:

<?php
$hashedPassword = "5f4dcc3b5aa765d61d8327deb882cf99"; // Example hashed password
$charset = "abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ0123456789"; // Character set
$maxLength = 5; // Maximum password length to consider

function bruteForce($password, $charset, $maxLength) {
    $charsetLength = strlen($charset);
    $startTime = microtime(true);

    for ($length = 1; $length <= $maxLength; $length++) {
        $combinations = pow($charsetLength, $length);

        for ($i = 0; $i < $combinations; $i++) {
            $guess = '';

            for ($j = 0; $j < $length; $j++) {
                $guess .= $charset[$i % $charsetLength];
                $i = (int)($i / $charsetLength);
            }

            if (md5($guess) === $password) {
                $endTime = microtime(true);
                $timeTaken = $endTime - $startTime;
                return [$guess, $timeTaken];
            }
        }
    }

    return [null, null];
}

list($originalPassword, $timeTaken) = bruteForce($hashedPassword, $charset, $maxLength);

if ($originalPassword) {
    echo "Password found: $originalPassword\n";
    echo "Time taken: $timeTaken seconds\n";
} else {
    echo "Password not found within the given constraints.\n";
}
?>

Output:

• If the hashed password is simple and matches the constraints, the program will find the password within seconds or minutes.
• For complex passwords, this method may take an impractical amount of time.

Method 2: Dictionary Attack

A dictionary attack is more sophisticated than brute force. Instead of generating every possible combination, it involves using a pre-built dictionary or wordlist of commonly used passwords. This method is more efficient than brute force, especially if the password is weak or commonly used.

Let's create a PHP program to demonstrate a dictionary attack:

<?php
$hashedPassword = "5f4dcc3b5aa765d61d8327deb882cf99"; // Example hashed password
$dictionary = file("passwords.txt", FILE_IGNORE_NEW_LINES); // Load a dictionary file

function dictionaryAttack($password, $dictionary) {
    $startTime = microtime(true);

    foreach ($dictionary as $guess) {
        if (md5($guess) === $password) {
            $endTime = microtime(true);
            $timeTaken = $endTime - $startTime;
            return [$guess, $timeTaken];
        }
    }

    return [null, null];
}

list($originalPassword, $timeTaken) = dictionaryAttack($hashedPassword, $dictionary);

if ($originalPassword) {
    echo "Password found: $originalPassword\n";
    echo "Time taken: $timeTaken seconds\n";
} else {
    echo "Password not found in the dictionary.\n";
}
?>

Output:

• If the hashed password exists in the dictionary, the program will find it quickly.
• For strong and unique passwords, this method may not yield any results.

Conclusion:

Converting a hashed password back to its original string is a complex and resource-intensive task. It's crucial to understand that password hashing is designed to be a one-way process for security reasons. Therefore, you should only attempt to reverse hashed passwords in legitimate and ethical situations, such as password recovery on your own system.

While methods like brute force and dictionary attacks are showcased in this blog, it's essential to emphasize that strong, unique passwords are the best defense against these reversal attempts. Always follow best practices for password security and hashing, and never store plaintext passwords.