Anti-Debugging Tricks (1993)

http://textfiles.com/programming/antidbg.txt

by antigizmo • 11 years ago

74 18 11 years ago

I remember hitting a few of these back in my youth when I was trying to "backup" game floppy disks. Some were easy to work around (eg 1.1.1 could just be replaced with NOP commands to allow further debugging), others were much more difficult to deal with (eg 2.2.2 resulted in single stepping through huge chunks of code, taking notes as I went, and rebooting/restarting the session each time I made a mistake - very time consuming).

I liked encountering a form of protection I hadn't seen before, it gave me a new challenge to solve and a chance to learn something new. I came to realise I didn't even care about the games themselves, bypassing the protection WAS the game for me.

As an aside, overall I noticed a positive correlation between the quality of the game and the quality of the protection (if any) it used.

tux• 11 years ago

Here is a bit easier to read version:

http://readtext.org/programming/anti-debugging-tricks/

bnjf• 11 years ago

Serge Pachkovksy's EDB can still be found at ftp://ftp.oldskool.org/pub/ANORMAL%20executable%20tools/DOSEXE%20Executable%20Tools%20Pack/tools/edb.015-Serge%20Pachkovsky/

jkot• 11 years ago

Most extreme trick was destruction code, which would only be executed while debugging, due to timing. Back than it was possible to destroy CRT display (set refresh frequency too high), motherboard (overwrite BIOS) or harddrive.

jacquesm5• 11 years ago

One particular nasty trick was a very tight loop with interrupts disabled writing 0 to a location that was 0xff in the ROM. The ROM and the CPU would end up fighting over this, it effectively shorts 5V through the databus drivers to ground. The goal here is not to damage some peripheral but to directly damage the CPU.

On more modern CPUs this trick should not longer work but on quite a few 8 bit micros it definitely did (let's not go into how I know this and how I know the ca. 1987 list price of a 6809).

kuschku4• 11 years ago

Time for a lawsuit, I guess?

Debugging is your right, and destroying your hardware is not something the software may do.

beagle32• 11 years ago

So, you're saying that the mythical HCF instruction[0] was somewhat real?

[0] https://en.wikipedia.org/wiki/Halt_and_Catch_Fire

0x4a42• 11 years ago

I remeber the CIH virus used to break motherboards by corrupting the BIOS.

krylon• 11 years ago

I remember reading a paper about how Skype attempts to foil attempts to run it under a debugger/tracer/whatever, and when Skype "thinks" it's being debugged, it will write random garbage to all registers and then branch to a random address. It had whole arsenal of tests to check if somebody was sneaking up on it, and it ran a couple of these, chosen randomly, at more-or-less regular intervals. Some programs really value their privacy.

kuschku4• 11 years ago

Or, in other words, some programs try to take their customers computers hostage.

Seriously, who would be willing to run software if they knew it would try to do everything to destroy your system (read the comments above about actual physical damage) when you try to understand it?

If you run the software on your system, it is yours. Debugging is, per ECJ decision, a human right. Your software, your right to take it apart and try to understand it.

I don’t get how people can accept to run such hostile software.

beagle32• 11 years ago

The author lists his fido addresses... I'm feeling nostalgic even though nostalgia isn't what it used to be.

A quick google shows that he headed Checkpoint's vulnerability research until recently. Another name on this article, Eden Shochat, is now running Aleph[0] - a VC with a blog worth reading.

[0] http://aleph.vc/

mattlutze• 11 years ago

A course I took this last semester spent quite a bit of time in assmebly, something I'd previously not done. I'd honestly like to see exploration of some of these tricks in those sorts of courses -- it's a really fascinating way to think about the light-side of the ASM force...

Anti-Debugging Tricks (1993)

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