Convert C# PBKDF2 using Rfc2898DeriveBytes to PHP

Question

Long story short have a membership system built in .NET that we are porting to WordPress and need to replicate the PBKDF2 encryption so users don't need to reset their passwords.

Using a know hashed password I've been able to replicate this in .NET easily, with the following code:

static void Main(string[] args)
{
  var isValid = CheckPassword("#0zEZcD7uNmv", "5SyOX+Rbclzvvit3MEM2nBRaPVo2M7ZTs7n3znXTfyW4OhwTlJLvpcUlCryblgkQ");
}

public static int PBKDF2IterCount = 10000;
public static int PBKDF2SubkeyLength = 256 / 8; // 256 bits
public static int SaltSize = 128 / 8; // 128 bits

private static bool CheckPassword(string Password, string ExistingHashedPassword)
{
  byte[] saltAndPassword = Convert.FromBase64String(ExistingHashedPassword);
  byte[] salt = new byte[SaltSize];

  Array.Copy(saltAndPassword, 0, salt, 0, SaltSize);

  Console.WriteLine("--Salt--");
  Console.WriteLine(Convert.ToBase64String(salt));

  string hashedPassword = HashPassword(Password, salt);

  Console.WriteLine("--HashedPassword--");
  Console.WriteLine(hashedPassword);

  return hashedPassword == ExistingHashedPassword;
}

private static string HashPassword(string Password, byte[] salt)
{
  byte[] hash = new byte[PBKDF2SubkeyLength];
  using (var pbkdf2 = new Rfc2898DeriveBytes(Password, salt, PBKDF2IterCount))
  {
    hash = pbkdf2.GetBytes(PBKDF2SubkeyLength);
  }

  byte[] hashBytes = new byte[PBKDF2SubkeyLength + SaltSize];
  Array.Copy(salt, 0, hashBytes, 0, SaltSize);
  Array.Copy(hash, 0, hashBytes, SaltSize, PBKDF2SubkeyLength);

  string hashedPassword = Convert.ToBase64String(hashBytes);
  return hashedPassword;
}

The console app will produce the following:

--Salt--
5SyOX+Rbclzvvit3MEM2nA==
--HashedPassword--
5SyOX+Rbclzvvit3MEM2nBRaPVo2M7ZTs7n3znXTfyW4OhwTlJLvpcUlCryblgkQ
--IsValid--
True

However in the PHP side I can't get the same results. My code so far is below.

$mySalt = base64_decode('5SyOX+Rbclzvvit3MEM2nA==');
$dev = pbkdf2('sha1', '#0zEZcD7uNmv', $mySalt, 10000, 48, true);
$key = substr($dev, 0, 32); //Keylength: 32
$iv = substr($dev, 32, 16); // IV-length: 16

echo 'PHP<br/>';
echo 'PASS: '.base64_encode($dev).'<br/>';
echo 'SALT: '.base64_encode($iv).'<br/><br/>'; 

echo '.NET<br/>';
echo 'PASS: 5SyOX+Rbclzvvit3MEM2nBRaPVo2M7ZTs7n3znXTfyW4OhwTlJLvpcUlCryblgkQ<br/>';
echo 'SALT: 5SyOX+Rbclzvvit3MEM2nA==<br/><br/>'; 

function pbkdf2($algorithm, $password, $salt, $count, $key_length, $raw_output = false)
{
    $algorithm = strtolower($algorithm);
    if(!in_array($algorithm, hash_algos(), true))
        die('PBKDF2 ERROR: Invalid hash algorithm.');
    if($count <= 0 || $key_length <= 0)
        die('PBKDF2 ERROR: Invalid parameters.');

    $hash_length = strlen(hash($algorithm, "", true));
    $block_count = ceil($key_length / $hash_length);

    $output = "";
    for($i = 1; $i <= $block_count; $i++) {
        // $i encoded as 4 bytes, big endian.
        $last = $salt . pack("N", $i);
        // first iteration
        $last = $xorsum = hash_hmac($algorithm, $last, $password, true);
        // perform the other $count - 1 iterations
        for ($j = 1; $j < $count; $j++) {
            $xorsum ^= ($last = hash_hmac($algorithm, $last, $password, true));
        }
        $output .= $xorsum;
    }
    return substr($output, 0, $key_length);
}

And the results are:

PHP
PASS: FFo9WjYztlOzuffOddN/Jbg6HBOUku+lxSUKvJuWCRCsYe+1Tgbb8Ob4FtxumMal
SALT: rGHvtU4G2/Dm+BbcbpjGpQ==

.NET
PASS: 5SyOX+Rbclzvvit3MEM2nBRaPVo2M7ZTs7n3znXTfyW4OhwTlJLvpcUlCryblgkQ
SALT: 5SyOX+Rbclzvvit3MEM2nA==

Any help would be appreciated.

Answer 1

Ended up getting it working using the https://github.com/defuse/password-hashing libraries, with some minor changes match the format of hashes I was working with database I'm importing.

But my main problem was with these lines where I'm trying to get a key out of a hash.

$dev = pbkdf2('sha1', '#0zEZcD7uNmv', $mySalt, 10000, 48, true);
$key = substr($dev, 0, 32); //Keylength: 32
$iv = substr($dev, 32, 16); // IV-length: 16

Changing it to the below, so that it is creating a hash hash that is 32 bits long and joining the returning hash to the salt fixed the issue.

$dev = pbkdf2('sha1', '#0zEZcD7uNmv', $mySalt, 10000, 32, true);
echo 'PASS: '.base64_encode($mySalt.$dev).'<br />';

With the output below now matching .NET:

PASS: 5SyOX+Rbclzvvit3MEM2nBRaPVo2M7ZTs7n3znXTfyW4OhwTlJLvpcUlCryblgkQ

Answer 2

I ran into this post while searching for a way to migrate passwords from a legacy Asp.Net MVC application to Laravel.

For those interested in just comparing the generated hash (ie. for authentication purpose), please consider the following:

function legacyHashCheck($hash, $password)
{
    $raw     = base64_decode($hash);
    $salt    = substr($raw, 1, 16);
    $payload = substr($raw, 17, 32);

    //new Rfc2898DeriveBytes(password, salt, 1000).GetBytes(32)
    $check   = hash_pbkdf2('sha1', $password, $salt, 1000, 32, true);

    return $payload === $check;
}