Delphi DEC library (Rijndael) encryption

Question

I am trying to use the DEC 3.0 library (Delphi Encryption Compedium Part I) to encrypt data in Delphi 7 and send it to a PHP script through POST, where I am decrypting it with mcrypt (RIJNDAEL_256, ECB mode).

Delphi part:

uses Windows, DECUtil, Cipher, Cipher1;

function EncryptMsgData(MsgData, Key: string): string;
var RCipher: TCipher_Rijndael;
begin
  RCipher:= TCipher_Rijndael.Create(KeyStr, nil);
  RCipher.Mode:= cmECB;
  Result:= RCipher.CodeString(MsgData, paEncode, fmtMIME64);
  RCipher.Free;
end;

PHP part:

function decryptMsgContent($msgContent, $sKey) {
    return mcrypt_decrypt(MCRYPT_RIJNDAEL_256, $sKey, base64_decode($msgContent), MCRYPT_MODE_ECB, mcrypt_create_iv(mcrypt_get_iv_size(MCRYPT_RIJNDAEL_256, MCRYPT_MODE_ECB), MCRYPT_RAND));
}

The problem is that the decryption from PHP doesn't work and the output is gibberish, differing from the actual data.

Of course, Delphi Key and PHP $Key is the same 24 characters string.

Now I know DEC 3.0 is old and outdated, and I'm not an expert in encryption and can't tell if the inplementation is actually Rijndael 256. Maybe someone can tell me how this implementation differs from PHP's mcrypt w/ RIJNDAEL_256. Maybe the keysize is different, or the block size, but can't tell this from the code. Here's an excerpt from Cipher1.pas:

const
{ don’t change this }
  Rijndael_Blocks =  4;
  Rijndael_Rounds = 14;

class procedure TCipher_Rijndael.GetContext(var ABufSize, AKeySize, AUserSize: Integer);
begin
  ABufSize := Rijndael_Blocks * 4;
  AKeySize := 32;
  AUserSize := (Rijndael_Rounds + 1) * Rijndael_Blocks * SizeOf(Integer) * 2;
end;

Side question:

I know ECB mode isn't recommended and I'll use CBC as soon as I get ECB working. The question is, do I have to transmit the generated IV in Delphi to the PHP script also? Or knowing the key is sufficient, like for ECB?

Answer 1

You are calling the TCipher.Create(const Password: String; AProtection: TProtection); constructor, which will compute a hash of the password before passing it to the Init method, which performs the standard key schedule of the implemented algorithm. To override this key derivation, use:

function EncryptMsgData(MsgData, Key: string): string;
var RCipher: TCipher_Rijndael;
begin
  RCipher:= TCipher_Rijndael.Create('', nil);
  RCipher.Init(Pointer(Key)^,Length(Key),nil);
  RCipher.Mode:= cmECB;
  Result:= RCipher.CodeString(MsgData, paEncode, fmtMIME64);
  RCipher.Free;

end;

Answer 2

OK, so to sum this up, there were 3 problems with my code:

1. Due to my poor understanding of mcrypt and ciphers in general, MCRYPT_RIJNDAEL_256 refers to 128 bits block and doesn't refer to the keysize. My correct choice should have been MCRYPT_RIJNDAEL_128, which is the AES standard and is also supported by DEC 3.0.

2. DEC has it's own default key derivation, so I needed to bypass it so I wouldn't have to implement it in PHP also. In actuality, I am using my own key derivation algorithm that was easy to reproduce in PHP (first 32 characters of sha1(key)).

3. DEC doesn't pad plaintext to a multiple of the block size of the cipher, as mcrypt expects, so I had to do it manually.

Providing working code below:

Delphi:

uses Windows, DECUtil, Cipher, Cipher1, CryptoAPI;

function EncryptMsgData(MsgData, Key: string): string;
var RCipher: TCipher_Rijndael;
    KeyStr: string;
begin
  Result:= '';
  try
    // key derivation; just making sure to feed the cipher a 24 chars key
    HashStr(HASH_SHA1, Key, KeyStr);
    KeyStr:= Copy(KeyStr, 1, 24);
    RCipher:= TCipher_Rijndael.Create('', nil);
    RCipher.Init(Pointer(KeyStr)^, Length(KeyStr), nil);
    RCipher.Mode:= cmECB;
    Result:= RCipher.CodeString(MsgData + StringOfChar(#0,16-(Length(MsgData) mod 16)), paEncode, fmtMIME64);
    RCipher.Free;
  except
  end;
end;

PHP:

function decryptMsgContent($msgContent, $sKey) {
    $sKey = substr(sha1(sKey), 0, 24);
    return trim(mcrypt_decrypt(MCRYPT_RIJNDAEL_128, $sKey, base64_decode($msgContent), MCRYPT_MODE_ECB, mcrypt_create_iv(mcrypt_get_iv_size(MCRYPT_RIJNDAEL_128, MCRYPT_MODE_ECB), MCRYPT_RAND)));
}

Answer 3

A 256 bit key I found is 32 charachters, or 32 bytes. Not 24. This may be the issue.

[EDIT]

I combined everyone's ideas (ansistring, etc) into one single idea with a fix.

Also, you are using codestring( -- it should be Encodestring(

I pasted working Encrypt and Decrypt source below:

---

function EncryptMsgData(MsgData, Key: AnsiString): AnsiString;
var RCipher: TCipher_Rijndael;
begin
  RCipher:= TCipher_Rijndael.Create('', nil);
  RCipher.Init(Pointer(Key)^,Length(Key),nil);
  RCipher.Mode:= cmCBC;
  Result:= RCipher.EncodeString(MsgData);
  RCipher.Free;
end;

function DecryptMsgData(MsgData, Key: AnsiString): AnsiString;
var RCipher: TCipher_Rijndael;
begin
  RCipher:= TCipher_Rijndael.Create('',nil);
  RCipher.Init(Pointer(Key)^,Length(Key),nil);
  RCipher.Mode:= cmCBC;
  Result:= RCipher.DecodeString(MsgData);
  RCipher.Free;
end;

---

Use that with a 32 charachter key and you get proper encryption and decryption.

In order to store and use the encrypted data as a string you may want to use Base64Encode(

But do not forget to Base64Decode prior to decrypting.

This is the same technique needed for Blowfish. Sometimes the charachters actually are like a backspace, and perform the function rather than showing on screen. Base64Encode basically converts the charachters to something you can display in text.

Prior to transferring the encoded data across the internet or to another application in the same or another language, you MUST base64encode and decode in order to not loose data. Don't forget it in PHP too!