xxx.pas

function XOR_F(const AFileName: string; const AKey: string): boolean;
var
  CopyBuffer: Pointer;
  TimeStamp, BytesCopied: Longint;
  Source, Dest: Integer;
const
  ChunkSize : LongInt = 8192;
begin
  GetMem(CopyBuffer, ChunkSize);
  try
    Source := FileOpen(AFileName, fmShareDenyWrite);
    if (Source < 0) then break;
    try
      Dest := FileCreate('xor_' + AFileName);
      if (Dest < 0) then break;
      try
        repeat
          BytesCopied := FileRead(Source, CopyBuffer^, ChunkSize);
          if (BytesCopied > 0) then
            FileWrite(Dest, CopyBuffer^, BytesCopied);
        until BytesCopied < ChunkSize;
      finally
        FileClose(Dest);
      end;
    finally
      FileClose(Source);
    end;
  finally
    FreeMem(CopyBuffer);
  end;
end;