.Net and PHP Rijndael encryption not matching

Question

At first i thought it was the padding since mcrypt uses zero padding but i changed the php to use PKCS7 and get the same exact results

Can anyone help? I think it has something to do with the padding in the php

Test output from .Net:

Key: d88f92e4fa27f6d45b49446c7fc76976
Text: Testing123
Encrypted: /DMkj7BL9Eu2LMxKhdGT+A==
Encrypted after base64 decode: ?3$??K?K?,?J???
Decrypted: Testing123

Test output from PHP:

Key: d88f92e4fa27f6d45b49446c7fc76976
Text: Testing123
Encrypted: K+ke5FNI5T6F6B/XvDF494+S8538Ze83cFz6v1FE89U=
Encrypted after base64 decode: +éäSHå>…è×¼1x÷’óüeï7p\ú¿QDóÕ
Decrypted: Testing123����������������������

PHP:

class rijndael{
var $mcrypt_cipher = MCRYPT_RIJNDAEL_256;
var $mcrypt_mode = MCRYPT_MODE_CBC;
function decrypt($pass, $encrypted)
{
    $encrypted = base64_decode($encrypted);
    $key = $this->getkey($pass);
    $iv = $this->getiv($pass);
    $decrypted = mcrypt_decrypt($this->mcrypt_cipher, $key, $encrypted, $this->mcrypt_mode, $iv);

    $block = mcrypt_get_block_size($this->mcrypt_cipher, $this->mcrypt_mode);
    $pad = ord($decrypted[($len = strlen($decrypted)) - 1]);
    return substr($decrypted, 0, strlen($decrypted) - $pad);

}
function encrypt($pass, $decrypted)
{
    $key = $this->getkey($pass);
    $iv = $this->getiv($pass);
    $block = mcrypt_get_block_size($this->mcrypt_cipher, $this->mcrypt_mode);
    $pad = $block - (strlen($str) % $block);
    $str .= str_repeat(chr($pad), $pad);
    $encrypted = mcrypt_encrypt($this->mcrypt_cipher, $key, $decrypted, $this->mcrypt_mode, $iv);
    return base64_encode($encrypted);
}
function getkey($passphrase)
{
    $L1 = base64_encode(hash("sha256", $passphrase, true));
    $L2 = $passphrase.$L1;
    return hash("sha256", $L2, true);
}
function getiv($passphrase)
{
    $L1 = base64_encode(md5($passphrase));
    $L2 = $passphrase.$L1;
    return md5($L2);
}
}

VB .Net:

Public Class RijnDael

    Public Shared Function Decrypt(ByVal sData As String, ByVal sKey As String)
        Dim bytData() As Byte = Encoding.UTF8.GetBytes(sData)
        Return Decrypt(bytData, sKey)
    End Function
    Public Shared Function Decrypt(ByVal bytData As Byte(), ByVal strPass As String) As Byte()
        Dim bytResult As Byte()
        Using oRM As New System.Security.Cryptography.RijndaelManaged
            oRM.KeySize = 256
            oRM.Key = GeKey(strPass)
            oRM.IV = GetIV(strPass)
            oRM.Mode = CipherMode.CBC
            oRM.Padding = PaddingMode.PKCS7
            Using oMS As New MemoryStream(bytData)
                Using oCS As New Cryptography.CryptoStream(oMS, oRM.CreateDecryptor, Security.Cryptography.CryptoStreamMode.Read)
                    Dim TempDecryptArr As Byte()
                    ReDim TempDecryptArr(bytData.Length)
                    Dim decryptedByteCount As Integer
                    decryptedByteCount = oCS.Read(TempDecryptArr, 0, bytData.Length)
                    '
                    ReDim bytResult(decryptedByteCount)
                    Array.Copy(TempDecryptArr, bytResult, decryptedByteCount)
                    '
                    oCS.Close()
                End Using
                oMS.Close()
            End Using
        End Using
        Return bytResult
    End Function

    Public Shared Function Encrypt(ByVal sData As String, ByVal sKey As String)
        Dim bytData() As Byte = Encoding.UTF8.GetBytes(sData)
        Return Encrypt(bytData, sKey)
    End Function
    Public Shared Function Encrypt(ByVal bytData As Byte(), ByVal strPass As String) As Byte()
        Dim bytResult As Byte()
        Using oRM As New Cryptography.RijndaelManaged
            oRM.KeySize = 256
            oRM.Key = GeKey(strPass)
            oRM.IV = GetIV(strPass)
            oRM.Mode = CipherMode.CBC
            oRM.Padding = PaddingMode.PKCS7
            Using oMS As New MemoryStream
                Using oCS As New Cryptography.CryptoStream(oMS, oRM.CreateEncryptor, Cryptography.CryptoStreamMode.Write)
                    oCS.Write(bytData, 0, bytData.Length)
                    oCS.FlushFinalBlock()
                    bytResult = oMS.ToArray()
                    oCS.Close()
                End Using
                oMS.Close()
            End Using
        End Using
        Return bytResult
    End Function

    Private Shared Function GeKey(ByVal strPass As String) As Byte()
        Dim bytResult As Byte()
        'Generate a byte array of required length as the encryption key.
        'A SHA256 hash of the passphrase has just the required length. It is used twice in a manner of self-salting.
        Using oSHA256 As New Cryptography.SHA256Managed
            Dim L1 As String = System.Convert.ToBase64String(oSHA256.ComputeHash(Encoding.UTF8.GetBytes(strPass)))
            Dim L2 As String = strPass & L1
            bytResult = oSHA256.ComputeHash(System.Text.Encoding.UTF8.GetBytes(L2))
            oSHA256.Clear()
        End Using
        Return bytResult
    End Function

    Private Shared Function GetIV(ByVal strPass As String) As Byte()
        Dim bytResult As Byte()
        'Generate a byte array of required length as the iv.
        'A MD5 hash of the passphrase has just the required length. It is used twice in a manner of self-salting.
        Using oMD5 As New Cryptography.MD5CryptoServiceProvider
            Dim L1 As String = System.Convert.ToBase64String(oMD5.ComputeHash(Encoding.UTF8.GetBytes(strPass)))
            Dim L2 As String = strPass & L1
            bytResult = oMD5.ComputeHash(System.Text.Encoding.UTF8.GetBytes(L2))
            oMD5.Clear()
        End Using
        Return bytResult
    End Function

End Class

Uneventful

Answer 1

The problems in your two pieces of code are:

• Use Rijndael-128 with a key and block size of 16 bytes / 128 bit in both the .NET and the PHP code. For Rijndael-256, your code generates an IV with the wrong length. And I don't know how to use AES-256 in PHP (key length of 32 bytes / 256 bits, block size of 16 bytes / 128 bit).

• Use of MD5: In the PHP code, add a second parameter true to the md5() function (in two places) so the result is binary data and not a hexadecimal string.

• In the encrypt() function in your PHP code, replace the variable $str with $decrypted (in two places). $str is never assigned a value and never used, so the padding has no effect.

If you fix these problems, then both programs will return the result:

Encrypted: /DMkj7BL9Eu2LMxKhdGT+A==

I haven't tried to decrypt it.

Vaios

Answer 2

For starters the 2 bits of code will create different initialization vectors (PHP is using sha256, and .net md5). And you're not truncating the PHP output by then first null char. There are several potential char set issues in the code too.

Pathology

I will check the iv's but they should be fine you just read the code wrong the keys on both sides use sha 256 and the ivs on both sides use md5 – Uneventful

The ivs weren't the same because .nets md5 outputs a md5 in 16 bytes instead of the 32 byte hexadecimal that php puts out. .net is now telling me: Specified initialization vector (IV) does not match the block size for this algorithm. the Rijndael block size is always 16 bytes so a 32 byte hex md5 wont work – Uneventful

I can make php output the md5 in a 16 byte format but mcrypt throws the error that the iv is not big enough then. how does mcrypt use a 32 byte iv when the iv is always 16 bytes for rijndael encryption? – Uneventful

I read wrong Rijndael, supports block and key sizes of 128, 192, and 256 bits, but in AES the block size is always 128 bits. The extra block sizes were not adopted by the AES standard. So I changed the blocksize to 256 and its working but they still dont match up – Uneventful