Re[2]: [Full-disclosure] (TOOL) TAPiON (Polymorphic Decryptor Generator) Engine

[Alejandro Barrera]

> Re,

>>...
>>If you want some indepth on polymorphis I recomend you the 29a papers:
>>http://vx.netlux.org/29a/

> I'm not a master in this branch however let me citate one of the
> aritcles found on the server you sent me (i also recomend you to read it):

I read it long ago thxs.

> Level 4: decryptor uses interchangeable instructions and changes
> their order (instructions mixing). Decryption algorithm remains unchanged.

> Level 5: all the above mentioned techniques are used, decryption
> algorithm is changeable, repeated encryption of virus code and even
> partial encryption of the decryptor code is possible. "
> ----- CUT --------------------------------------------------------------


> So appending to this source i got a level 3 or level 4, unless you fully
> understand the source. I'm not saying it is perfect, is was written in 5
> days.

Well, at least what I've seen is a level 3 polymorphism, due to the fact that
you don't perform instrucction mixing, but block mixing which is quite
different.

Don't get me wrong, I love to see this kind of source and I'm a great fan of
polymorphic engines Just making a note that your approach needs a little
bit more of tweaking

> Hope this helps you.


> best regards,
> Piotr Bania

Greets.



--
Alejandro Barrera García-Orea
R&D Engineer
c/ Alcala 268 28027 Madrid
Office: +34 91 326 66 11
Fax: +34 91 326 66 11
e-mail: abarrera@iron-gate.net

[Alejandro Barrera]

> Hi,

> TAPiON engine was developed to avoid code detection (shellcode/whatever).

Hi Piotr,
I had a look at Tapion's code and I don't relly see any trully genuin
polymorphism. Actually I did see some fixed patterns which could make
Tapion's decryptors pretty detectable:

The main problem is that you build the decryptor based on some blocks
which can be made into patterns, specially because the block
construction is always the same:

1) XOR block [optional with 50% of probabilities]
2) (mov block | get_eip block) or
(get_eip block | anti_emu block [1/3 prob] | mov block) [50% prob]
3) anti_emu block [1/3 prob]
4) -- Decryptor loop --
(copy_reg block | mov_reg block) or
(mov_reg block | copy_reg block | temp block ) [50% prob]
...

As you see, there is nearly no randomnes in the process and the
construction blocks are easy to detect.

If you want some indepth on polymorphis I recomend you the 29a papers:
http://vx.netlux.org/29a/


> best regards,
> Piotr Bania

Kindest regards

--
Alejandro Barrera García-Orea
R&D Engineer
c/ Alcala 268 28027 Madrid
Office: +34 91 326 66 11
Fax: +34 91 326 66 11
e-mail: abarrera@iron-gate.net