Delphi DEC Twofish Encryption and server-side decryption in PHP

Question

I have to encrypt string in Delphi with Twofish/CBC algorithm, send it to server and decrypt there. I've tested the code below, and B64 encoding/decoding process works, however I'm stuck at cipher encryption/decryption.

I am using DEC 5.2 for Delphi.

Here is the Delphi code that does the encryption:

class function TEncryption.EncryptStream(const AInStream: TStream; const AOutStream: TStream; const APassword: String): Boolean;
var
  ASalt: Binary;
  AData: Binary;
  APass: Binary;
begin
  with ValidCipher(TCipher_Twofish).Create, Context do
  try
    ASalt := RandomBinary(16);
    APass := ValidHash(THash_SHA1).KDFx(Binary(APassword), ASalt, KeySize);
    Mode := cmCBCx;
    Init(APass);

    EncodeStream(AInStream, AOutStream, AInStream.Size);
    result := TRUE;
  finally
    Free;
    ProtectBinary(ASalt);
    ProtectBinary(AData);
    ProtectBinary(APass);
  end;
end;

class function TEncryption.EncryptString(const AString, APassword: String): String;
var
  instream, outstream: TStringStream;
begin
  result := '';
  instream := TStringStream.Create(AString);
  try
    outstream := TStringStream.Create;
    try
      if EncryptStream(instream, outstream, APassword) then
        result := outstream.DataString;
    finally
      outstream.Free;
    end;
  finally
    instream.Free;
  end;
end;

And PHP function that is supposed to decrypt sent data:

function decrypt($input, $key) {
    $td = mcrypt_module_open('twofish', '', 'cbc', '');
    $iv = mcrypt_create_iv(mcrypt_enc_get_iv_size($td), MCRYPT_RAND);
    mcrypt_generic_init($td, $key, $iv);

    $decrypted_data = mdecrypt_generic($td, base64_decode_urlsafe($input));

    mcrypt_generic_deinit($td);
    mcrypt_module_close($td);

    return $decrypted_data;
}

I beleive I have to fiddle a bit more with salt and initialization vectors, however I have no idea how. From what I understand, KDFx() function makes SHA1 hashed password out from user password and salt, but I'm pretty much stuck at that point.

Answer 1

KDFx is an proprietary incompatible key derivation method, from the source: "class function TDECHash.KDFx // DEC's own KDF, even stronger". You will have problens using this from DEC and PHP and should use other libraries. The problem is discussed eg in http://www.delphipraxis.net/171047-dec-5-2-mit-vector-deccipher-umbau-von-dot-net-auf-delphi.html