AES encryption with Header

[randy_dom]

I use the following the Code to encrypt my file using EAS algo :

I use this Interface to the AES functions written by Brian Gladman :AES Interface by Brian Gladman

Delphi-Quellcode:

 const  HeadSig   = 'mee'; // Header Sig
type
  TMyFileHead = packed record
    Signature  : array  [0..2] of char; // header sig
    flVer    : String [4];// File Version
  end;
type
{ * encryption routine *}
function Enc(inStream, outStream :TStream; Header: TMyFileHead; const PWD :String='') : boolean;
begin
  inStream.Seek(0,soFromBeginning);
  outStream.Write(Header,SizeOf(TMyFileHead));// Write my Header Info to the Stream
 outStream.Seek(SizeOf(Header),soFromBeginning);
// Start the AES encryption routine 
  with TEncryption.Create(PWD,defCryptBufSize) do begin
  if EncryptStream(inStream,outStream) then
  result:=true
  else
  result:=false;
   Free;
    end;
end;
// example Of use 
procedure TForm1.Button3Click(Sender: TObject);
var 
   H    : TMyFileHead;
   F    : TMemoryStream;
   F1   : TMemoryStream;
begin
   H.Signature:=HeadSig;// write my header Signature "mee"
   F  := TMemoryStream.Create;
   F1 := TMemoryStream.Create;
   F.LoadFromFile('myfile.txt');
   // encrypt myfile.txt
   if Enc(F,F1,H)then
   F1.SaveToFile(ChangeFileExt('myfile.txt','.enc'));
   F.Free;
   F1.Free;
end; 

{ * decryption routine *}
function Dec(inStream, outStream :TStream; var Header: TMyFileHead; const PWD :String=''):boolean;
begin
 inStream.Seek(0,soFromBeginning);
  inStream.Read(Header,SizeOf(TMyFileHead));
// file header<>'mee'
  if Header.Signature <> HeadSig then
  begin
  // invalid File Signature so Stop the Decryption Operation .
    Result := False;
    Exit;
  end; 
  inStream.Seek(0,SizeOf(TMyFileHead));
  outStream.Seek(0,soFromBeginning);
 with TEncryption.Create(PWD,defCryptBufSize) do begin
 if DecryptStream(inStream,outStream,instream.Size) then
 result:=true
  else
  result:=false;
   Free;
  end;

// example of use
procedure TForm1.Button4Click(Sender: TObject);
var
  F    : TMemoryStream;
  F1   : TMemoryStream;
  h    : TMyFileHead;
begin
  F  := TMemoryStream.Create;
  F1 := TMemoryStream.Create;
// load the encrypted file
  F.LoadFromFile('myfile.enc');
  if Dec(F,F1,H) then
  // save the decrypted file 
  f1.SaveToFile(ChangeFileExt('myfile.enc','.dec'));
  F.Free;
  F1.Free;

end;

end;

the encryption Routine works well but the decryption is not working and no file is being saved .

What's incorrect with my Decryption Routine please ??

[Klaus01]

Hi there,

Delphi-Quellcode:

  if Dec(F,F1,H) then
    begin
     f1.position:=0;  // new
     // save the decrypted file
     f1.SaveToFile(ChangeFileExt('myfile.enc','.dec'));
    end;
  else
     showMessage('error ind dec')
  F.Free;
  F1.Free;

does dec give a true or false back?

Best regards
Klaus

[randy_dom]

thank you Klaus01 , now it works ( what a worse error i did in forgetting the f1 reposition )....

the dec result is based on the DecryptStream() result .

Zitat:

if DecryptStream(inStream,outStream,instream.Size) then {* dec :=True otherwise Dec:=False*}

[randy_dom]

i've noticed that in the decrypted file there's an extra string added at the end of file i think it's the Header Info !!!