Re: Converting PHP code to C#?

[mike <mike503@xxxxxxxxx>]

On 9/7/07, Symbian <mail5205772@xxxxxxxxxxxx> wrote:
>
> I'm unable to workout how to get the same IV as the one generated by the PHP
> script is random. The thing is that we cant change the PHP script as its
> readily being used now. Maybe I should look at the encryption routine and
> reverse that first?

just hard code the IV in both places.

to make it difficult you can do something like this (basically our
.NET guy took it from
http://www.codeproject.com/dotnet/DotNetCrypto.asp)

public static string Encrypt(string clearText, string Password)
    {
        // First we need to turn the input string into a byte array.
        byte[] clearBytes =
          System.Text.Encoding.UTF8.GetBytes(clearText);

PasswordDeriveBytes pdb = new PasswordDeriveBytes(Password,
            new byte[] {0x49, 0x76, 0x61, 0x6e, 0x20, 0x4d,
            0x65, 0x64, 0x76, 0x65, 0x64, 0x65, 0x76});

 byte[] encryptedData = Encrypt(clearBytes,
                 pdb.GetBytes(32), pdb.GetBytes(16));

   return Convert.ToBase64String(encryptedData);

}

(make sure to copy that first Encrypt method and set alg.Padding =
PaddingMode.Zeros)

and on PHP side (the IV/key numbers have been changed to protect the
innocent :))

i believe the numbers are the decimal values of the .NET 0x49 etc. you
need 32 of them for the key, and 16 for the IV (to match the
parameters above) - these numbers do not match right now i just
jumbled them up. i would first see if you can use my code to properly
encrypt in .NET and decrypt in PHP. then hopefully you can just
reverse it.

what i should do is actually publish an example with working
instructions + numbers. i'll keep this email around and publish an
article on my blog or something hopefully soon.

function decrypt($text, $key) {
        $enc_key_array = Array(24,91,81,138,122,etc);
        $chrs = "";
        foreach(array_values($enc_key_array) as $chr) {
                $chrs .= chr($chr);
        }
        $enc_key = $chrs;
        $enc_iv_array = Array(35,56,103,81,77,etc);
        $chrs = "";
        foreach(array_values($enc_iv_array) as $chr) {
                $chrs .= chr($chr);
        }
        $enc_iv = $chrs;
        $text = base64_decode($text);
        $decrypted = mcrypt_decrypt(MCRYPT_RIJNDAEL_128, $enc_key,
$text, "cbc", $enc_iv);
        return $decrypted."\n";
}

remember to base64 encode/decode at the proper times. we use this to
encrypt information in a cookie so it needs to be encoded for transit.
it also helps when you are copy/pasting it back and forth to test
encrypt/decrypt :)

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