I need help resolving a Lazarus FPC Blowfish library usage problem

Question

I have been using the Lazarus/FPC Blowfish library to encrypt file streams a while, and it works very well for me.

Now I tried to adapt the library to encrypt and decrypt arbitrary memory structures (records, but also strings), and got a problem which I could not resolve in days, so please help.

Problem is that strings having a length beeing an exact multiple of the Blowfish block size (8 Bytes) are encrypted and decrypted properly. If a string does not end at an exact 8 Byte boundary, the characters exceeding the boundary are mangled.

Here is the code (for the complete Lazarus project please follow the link)

Link to Lazarus project zip

Procedure BlowfishEncrypt(var Contents;ContentsLength:Integer;var Key:String);

// chop Contents into 64 bit blocks and encrypt using key

var
  arrShadowContent:Array of Byte absolute Contents;
  objBlowfish: TBlowFish;
  BlowfishBlock: TBFBlock;
  ptrBlowfishKey:PBlowFishKey;
  p1,count,maxP:integer;

begin
  ptrBlowfishKey := addr(Key[1]);
  objBlowfish := TBlowFish.Create(ptrBlowfishKey^,Length(Key));
  p1 := 0;
  maxP := ContentsLength - 1;
  count := SizeOf(BlowfishBlock);
  while p1 < maxP do
     begin
     fillChar(BlowfishBlock,SizeOf(BlowfishBlock),0); // only for debugging
     if p1 + count > maxP then
        count := ContentsLength - p1;
     Move(arrShadowContent[p1],BlowfishBlock,count);
     objBlowfish.Encrypt(BlowfishBlock);
     Move(BlowfishBlock,arrShadowContent[p1],count);
     p1 := p1 + count;
     end;
  FreeAndNil(objBlowfish);
end;

And this is the call ...

procedure TForm1.CryptButtonClick(Sender: TObject);

var
  ContentsBuffer,Key:String;

begin
ContentsBuffer := PlainTextEdit.Text;
Key := KeyTextEdit.Text;
BlowFishEncrypt(ContentsBuffer,Length(ContentsBuffer),Key);
CryptOutEdit.Text := ContentsBuffer;
BlowFishDecrypt(ContentsBuffer,Length(ContentsBuffer),Key);
CryptCheckEdit.Text := ContentsBuffer;
end; 

And here you see what's happening:

Screenshot of Test GUI

Answer 1

Resolved. The problem is that I am not allowed to truncate a TBFBlock. For Blowfish Decryption to work, ContetLength must be a multiple of TBFBlock size.