Mega Code Archive
Protecting code the ... dizzy way
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Title: Protecting code the ... dizzy way
Question: Code crackers do not only use debuggers but also reverse dissassemblers, that allow viewing code in a more readable form.
Crackers set breakpoints (typically on windows calls or messages), and "peek" on the source code before actually single-stepping back.
This is a small example of how to insert VARIABLE dummy code between valid statements, which can make reverse-dissassembling and single-stepping a nightmare.
Answer:
Conditional ASM statements that actually insert dummy code are of this kind:
JMP here
DB byte,byte,byte,byte ; garble data
here:
so actually the garble data never get executed. One can find a LOT of combinations that actually drive reverse dissassemblers nuts. This
include file, when used, includes variable length dummy statements
----- This is the Include file AsmDizzy.inc: ------
{$IFDEF DIZZY4}
{$UNDEF DIZZY1}
{$UNDEF DIZZY2}
{$UNDEF DIZZY3}
{$UNDEF DIZZY4}
{$ENDIF}
{$IFDEF DIZZY3}
{$IFNDEF DIZZY4}
Asm
DB $EB,$06,$55,$44,$55,$03,$a8,$09;
end;
{$DEFINE DIZZY4}
{$ENDIF}
{$ENDIF}
{$IFDEF DIZZY2}
{$IFNDEF DIZZY3}
{$IFNDEF DIZZY4}
Asm
DB $EB,$04,$75,$13,$a2,$14;
end;
{$DEFINE DIZZY3}
{$ENDIF}
{$ENDIF}
{$ENDIF}
{$IFNDEF DIZZY1}
{$IFNDEF DIZZY2}
{$IFNDEF DIZZY3}
{$IFNDEF DIZZY4}
Asm
DB $EB,$04,$55,$03,$a7,$44;
end;
{$DEFINE DIZZY2}
{$ENDIF}
{$ENDIF}
{$ENDIF}
{$ENDIF}
;
---- End of incude file ----
Having this include file, try putting this code in the event of
a button click. The code executes normally, but a lot of VARIABLE
garble code is between the statements, some times 4,5 or 6 bytes wide.
procedure TForm1.Button1Click(Sender: TObject);
begin
{$I AsmDizzy.inc}
ShowMessage('1');
{$I AsmDizzy.inc}
ShowMessage('2');
{$I AsmDizzy.inc}
ShowMessage('3');
{$I AsmDizzy.inc}
ShowMessage('4');
{$I AsmDizzy.inc}
ShowMessage('1');
end;
This can make singlestepping a nightmare, even with simple statements
(ShowMessage) in-between. The .inc file can be enhanced to produce
real random code, but this is a task for you to do.
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