Linux cracking: the live approach (acrobat reader)
(Linux advanced reverse engineering: imported functions)

by SiuL+Hacky
Petit image

(November 1997)

Courtesy of fravia's

Well, another VERY remarkable essay, that I am proud to present. SiuL+Hacky tackles here once more UNCOVERED ground, and teaches all of you more elements of Linux reverse engineering... you may want to check somewhere on the web his good "siulin1.htm", first essay about Linux reverse engineering... a bad omen of these more and more commercial times... even Linux is getting soiled by commercial overbloated applications :-(



In my first linux essay you could get an introduction on how to port our
windoze techniques to the linuz world. It was mainly dedicated to dead
approach, because it is really powerful for some kind of programs. But
sadly, as you'll see, huge and overbloated programs are getting into Linux
and if you want to reverse engineer your target you need some debugging 
(unless you are a 'senior' mental cracker).

With this essay I'll try to introduce you the linux graphic environment,
XWindows (no kind of porno environment eh !). It may look like Windoze but
internally is very different in some aspects. The main difference is that it
uses the ubiquitous client-server scheme. Anyway, I don't have the time nor
the knowledge (+ hcu 1999 ?) to teach you thoroughly how it works, but
I'll show the starting point for cracking X applications. In linux you can
use several X servers, the most popular is XFree86 server but I hope that 
any of them will do it.

+ORC's proposal for cracking acrobat-pdf tools is a good opportunity for
practising these methods. I told you, as I told him, that I think is not
worthy losing time writing a text-to-pdf converter, because it does exist
and there are still several uncracked (and important) protection schemes. 
So, here I'm gonna crack Acrobat Reader (yes, it is available for linux, 
though the same windoze restrictions apply) with two main goals :

- I want to see always Menu and Toolbars.
- I don't want copy text restrictions and so on.

I got it from a Spanish magazine, but I suppose it is freely available at 
Adobe's site. You realise this is not reverse engineering pdf-format but 
Acrobat Reader. (I would like to see other people reverse engineer the 

II. ToolX of the Trade.

Obviously here you'll find some X-specific tools. Most of the tools I told
you in my first essay apply for X-RE. Especially useful is gonna be DASM,
because, though we are gonna use the live approach, the assembler listing is
again invaluable. I repeat you that this will give the clues, but for a
better use of them, READ the manual pages of them.

* xwininfo    -----------------------------------------------------------------

 This utility gives you information about a specific window. By default it asks 
to click on the target window you want to gather information. Be careful, and 
don't think here about "window" in the Windoze way. When I click with the mouse 
on a window, I'm clicking on the "physical" window, on the super-parent window 
(called root window) if you want to put it that way. Each window (buttons for 
instance are child windows) has an identifier. These are some useful switches:

- tree: Display all windows (root, parent and children) in a recursive way. It 
displays the identifier (known as Drawables) , the size, position and show on. 
Here is an example taken for Acrobat Reader:

xwininfo: Window id: 0x2800128 "Acrobat Reader"
 Root window id: 0x26 (the root window) (has no name)
   Parent window id: 0x8001ad (has no name)
        1 child:
             0x2800129 (has no name): ()  272x367+0+0  +527+121
             ... some other windows ...
 0x2800148 (has no name): ()  24x24+3+3  +530+183; << toolbar button
 0x2800147 (has no name): ()  24x24+27+3  +554+183;<< toolbar button
 0x2800146 (has no name): ()  24x24+51+3  +578+183;<< toolbar button
 0x2800145 (has no name): ()  6x24+75+3 +602+183
 0x2800144 (has no name): ()  24x24+81+3  +608+183;<< toolbar button
 0x2800143 (has no name): ()  24x24+105+3  +632+183;<<toolbar button
 0x2800142 (has no name): ()  24x24+129+3 +656+183; << and more ...
 0x2800141 (has no name): ()  6x24+153+3  +680+183
 0x2800140 (has no name): ()  24x24+159+3  +686+183
 0x280013f (has no name): ()  24x24+183+3 +710+183
 0x280013e (has no name): ()  24x24+207+3  +734+183
 0x280013d (has no name): ()  24x24+231+3  +758+183
 0x280013c (has no name): ()  6x24+255+3 +782+183
 0x280013b (has no name): ()  24x24+3+30  +530+210
 0x280013a (has no name): ()  24x24+27+30  +554+210
 0x2800139 (has no name): ()  6x24+51+30 +578+210
 0x2800138 (has no name): ()  24x24+57+30  +584+210
 0x2800137 (has no name): ()  24x24+81+30  +608+210
 0x2800136 (has no name): ()  24x24+105+30 +632+210
 0x2800135 (has no name): ()  6x24+129+30  +656+210
 0x2800134 (has no name): ()  24x24+135+30  +662+210
 0x2800133 (has no name): ()  6x24+159+30+68 6+210            
            ... some other windows ...

Of course, the first hex number is the window identifier, that will be
especially useful for other, or even this, tool.

-id : with this option you don't need to click on a specific window but you
can gather information for any window in particular.

-all: display all the information available.

* xev  ----------------------------------------------------------------------

This utility reports all the events involved with some window. Switches:

-id: If you don't give it an identifier, xev will display a test window,
where you can test mouse, keyboard and other kinds of event.

In some cases you may use this program for matching identifiers. For example
if run xev -id 0x2800148
But you don't know what window (child window) has this identifier! Just
move your mouse over the windows and you'll get messages just when 
you'll be over the window you are looking for (BTW MotionNotify events).

* xxgdb  --------------------------------------------------------------------

It is just the Xwindows front end for gdb. The only addition is a ButtonBar
with some useful commands. We'll see some useful commands while debugging
acrobat reader. I hope, in a future essay, to show some more friendly tools,
but as for now this is the most widespread and stable tool I know of.

* XWindows API Reference  ----------------------------------------------------

Working with Windoze programs, it turned important to know some "regular"
API calls like MessageBox, GetDlgItemText and so on. Well, the same apply, 
or will apply, for XWindows. You may get the call definitions in the .h files
located usually in the directory /usr/X11R6/include/X11. I found particularly
interesting a document available at xfree86 site (, or, even better, 
look for a mirror in a ftpsearch:

xlib.PS.Z   (971 Kb)

This is a 400 pages PostScript document where you'll find a lot of information.
It's hard to find books about Xwindows programming, so if you know some
tutorial or some document useful for our purposes,  send them to the +HCU to 
be included in the next revision of this essay.

* Text-to-pdf converters -----------------------------------------------------

This does exist (there's a good document about it at fravia's pdf project
page), and you'll need it for testing Acrobat Reader. It is necessary to 
get a fully unprotected document and test it against protected ones. 
I converted text to pdf passing through a PostScript intermediate stage.

mpage: this program converts text to PostScript easily.

GhostScript: this is not only a PostScript viewer, but it has a built-in
PostScript to pdf converter. If you don't want to go into GhostScript
internals (a hell for me), use pstoedit, for example, to manage this task.

III. Reverse Engineering Acrobat Reader.

Let's suppose Acrobat is the base directory where it is installed. You'll
find easily that it is invoked with "acrobat", a file in Acrobat/bin
directory with just 8467 bytes. Impossible for this huge monster (you'll
see). It is just a Shell Script that calls the huge monster
Acrobat/Reader/intellinux/acroread, 2.511.477 bytes full of nops (believe
me, I had a look). Ok, dasm it and the monster will be a ghastly hideous 
creature of 38.625.635 bytes and almost 1 million lines. 
I do recommend you not to edit it, and use the "less" viewer (with the 
searching capabilities you need).

Have a look at the symbol table (with the name of the functions, inside and
outside the program. Very nice gift from the Adobe's guys), and what should 
be a reverser bliss will be a cracker curse: MORE THAN 16000 functions (many 
of them repeated) with names as amazing as :


and bla, bla, bla.

I started writing down some name that could be interesting, then I started
skimming through and finally I scrolled them away. I am going to show you the
functions I saw suspicious. At the end of the essay you'll realise it could
have been very easy with a little Zen cracking, but I was not completely 
lucky (and for once I didn't want to be lucky) and I used the methodical 
approach that always saves you when your Zen is broken. Look at the 
following names:


I had a look at the code of these functions, and thne I tested them with 
the debugger, setting breakpoints and watching returned values. I got 
nothing, so I just searched once more, this time for the string "Hide". 
I wrote down these functions:


Looking the code of the last one I was lucky, help yourself:

Referenced from jump/call at 08062c64 ; 

08048500 <UnixMenubarWidgetHide>    pushl  %ebp
08048501 <UnixMenubarWidgetHide+1>  movl   %esp,%ebp
08048503 <UnixMenubarWidgetHide+3>  subl   $0x10,%esp
08048506 <UnixMenubarWidgetHide+6>  pushl  %ebx
08048507 <UnixMenubarWidgetHide+7>  movl   0x10(%ebp),%ebx
0804850a <UnixMenubarWidgetHide+a>  movb   %bl,0xffffffff(%ebp)
0804850d <UnixMenubarWidgetHide+d>  movl   0x8(%ebp),%eax
08048510 <UnixMenubarWidgetHide+10> pushl  %eax

Reference to function : AVMenubarGetServerData

08048511 <UnixMenubarWidgetHide+11> call   08089090  << I always thought that         
                                                     << this function could be 
                                                     << important... I was wrong
....  code and code ....

08048590 <UnixMenubarWidgetHide+90> movl   0xfffffff8(%ebp),%eax
08048593 <UnixMenubarWidgetHide+93> cmpb   $0x0,0x4(%eax)        << compare something
08048597 <UnixMenubarWidgetHide+97> jne    080485bc              << if not zero return and do nothing
08048599 <UnixMenubarWidgetHide+99> cmpb   $0x0,0xffffffff(%ebp) << if local var = 0 some SHOWING
0804859d <UnixMenubarWidgetHide+9d> je     080485b0              << else some HIDING
0804859f <UnixMenubarWidgetHide+9f> movl   0xc(%ebp),%eax
080485a2 <UnixMenubarWidgetHide+a2> pushl  %eax

Reference to function : UnixMenubarWidgetHideInternal

080485a3 <UnixMenubarWidgetHide+a3> call   08048480
080485a8 <UnixMenubarWidgetHide+a8> addl   $0x4,%esp
080485ab <UnixMenubarWidgetHide+ab> jmp    080485bc
080485ad <UnixMenubarWidgetHide+ad> nop    
080485ae <UnixMenubarWidgetHide+ae> nop    
080485af <UnixMenubarWidgetHide+af> nop    

Referenced from jump/call at 0804859d ; 

080485b0 <UnixMenubarWidgetHide+b0> movl   0xc(%ebp),%eax
080485b3 <UnixMenubarWidgetHide+b3> pushl  %eax

Reference to function : UnixMenubarWidgetShowInternal

080485b4 <UnixMenubarWidgetHide+b4> call   080484d0
080485b9 <UnixMenubarWidgetHide+b9> addl   $0x4,%esp

Referenced from jump/call at 08048597 ; 080485ab ; 

080485bc <UnixMenubarWidgetHide+bc> movl   0xffffffec(%ebp),%ebx
080485bf <UnixMenubarWidgetHide+bf> movl   %ebp,%esp
080485c1 <UnixMenubarWidgetHide+c1> popl   %ebp
080485c2 <UnixMenubarWidgetHide+c2> ret

What happen with that important variable ? If you look at instruction
804850, it is copied from one of the parameters of the function. With some
basic parameter theory (if not, read fravia's+ good "filemon" series) 
you know that :

1st parameter is located at [bp+0x8]
2nd parameter is located at [bp+0xc]
3rd parameter is located at [bp+0x10]

(of course, if we consider one parameter = one word length). Ok, let's have
a look at the caller (this function is called from 08062c64). Pay attention
to the parameters please:

(... some lines not important ...)
Reference to function : AVDocGetKioskBool

08062c24 <UnixDocViewUpdateVisibility+44> call   0807d290     <<<< the function returns 1 or 0 into  eax
08062c29 <UnixDocViewUpdateVisibility+49> addl   $0x8,%esp
08062c2c <UnixDocViewUpdateVisibility+4c> movl   %eax,%edx
08062c2e <UnixDocViewUpdateVisibility+4e> movsbl %dl,%eax     << the returned value is in eax again
08062c31 <UnixDocViewUpdateVisibility+51> jmp    08062c42     << look at these nops,
08062c33 <UnixDocViewUpdateVisibility+53> nop                 << nop                 << kind of mega-pentium alignment or room for patching?
08062c33 <UnixDocViewUpdateVisibility+53> nop    
08062c34 <UnixDocViewUpdateVisibility+54> nop    
08062c35 <UnixDocViewUpdateVisibility+55> nop    
08062c36 <UnixDocViewUpdateVisibility+56> nop    
08062c37 <UnixDocViewUpdateVisibility+57> nop    
08062c38 <UnixDocViewUpdateVisibility+58> nop    
08062c39 <UnixDocViewUpdateVisibility+59> nop    
08062c3a <UnixDocViewUpdateVisibility+5a> nop    
08062c3b <UnixDocViewUpdateVisibility+5b> nop
08062c3c <UnixDocViewUpdateVisibility+5c> nop    
08062c3d <UnixDocViewUpdateVisibility+5d> nop    
08062c3e <UnixDocViewUpdateVisibility+5e> nop    
08062c3f <UnixDocViewUpdateVisibility+5f> nop    

Referenced from jump/call at 08062c0b ; 

08062c40 <UnixDocViewUpdateVisibility+60> xorl   %eax,%eax

Referenced from jump/call at 08062c31 ;          << we are JUMPING TO HERE !!!!!!!!!!
                                                 << more nooping, if +orc would see this :-(
08062c42 <UnixDocViewUpdateVisibility+62> jmp    08062c55
... (10 more nops)...    
08062c4f <UnixDocViewUpdateVisibility+6f> nop    

Referenced from jump/call at 08062c05 ; 
08062c50 <UnixDocViewUpdateVisibility+70> movl   $0x1,%eax

Referenced from jump/call at 08062c42 ;        << we are JUMPING HERE!!!
08062c55 <UnixDocViewUpdateVisibility+75> pushl  %eax    <<saved 3rd parameter
                                                            << remember eax= returned value
08062c56 <UnixDocViewUpdateVisibility+76> movl   0x8(%ebp),%eax
08062c59 <UnixDocViewUpdateVisibility+79> movl   0x10(%eax),%edx
08062c5c <UnixDocViewUpdateVisibility+7c> pushl  %edx    <<saved 2nd parameter
08062c5d <UnixDocViewUpdateVisibility+7d> movl   0x8(%ebp),%eax
08062c60 <UnixDocViewUpdateVisibility+80> movl   0xc(%eax),%edx
08062c63 <UnixDocViewUpdateVisibility+83> pushl  %edx     <<saved 1st parameter
Reference to function : UnixMenubarWidgetHide
08062c64 <UnixDocViewUpdateVisibility+84> call   08048500

It is pretty clear, if the function AVDocGetKioskBool returns 0 we are GOOD
GUYS. Let's make this function return always 0. You could patch it the old
way, but now we are going to learn some xxgdb capabilities:

1) Fire acrobat reader of course. Look its Process Identifier (PID)
2) Fire xxgdb
3) Execute command "file (your path)/Acrobat/Reader/intellinux/bin/acroread,
   that will load the symbols. Don't worry if xxgdb complains about
4) Now we are gonna "join" the debugger to a running process. For this
   reason, execute the command "attach PID", where PID IS A NUMBER, the
   process identifier of acroread (use ps for checking)
5) You'll land probably in the middle of a system call, it is OK.
6) Run "cont" command to continue execution.
7) When you want to break, press Control-C.

This is the important code of AVDocGetKioskBool:

0807d3d2  movl   %edx,%eax
0807d3d4  jmp    0807d3e0 

(... another dozen of nops ...)

Referenced from jump/call at 0807d2bb ; 0807d3d4 ; 

0807d3e0  leal   0xfffffff0(%ebp),%esp
0807d3e3  popl   %ebx
0807d3e4  popl   %esi
0807d3e5  movl   %ebp,%esp
0807d3e7  popl   %ebp
0807d3e8  ret  

The instruction at 807d3e0 is always reached from 807d3d4, the other
reference is just a "fast return" when gets an error. This will do the
crack while working with the debugger. You'll see that this is a really
powerful debugger, with features supported by softice not a long time 
(xxgdb) is the prompt:

(xxgdb) br *0x0807d3d2 if $edx==1
Breakpoint 1 at 0x0807d3d2
(xxgdb) commands
>set $edx=0

Really powerful eh ? If you want to know the breakpoint status run 
"info br". 
Well if you now execute "cont", you'll always have menu, toolbars and 
so on visible, even if ghiribizo or whoever doesn't want :-). 
I think that the above code is pretty easy to understand.

And now what's up with the second part ? Specifically: 'copying text'. 
As I told you, I was not so lucky. Firstly I tried to play the same 
game, try and error, feel a little, look at suspicious functions... and  
I got lost in the mare magnum of silly functions. I navigated over tons 
of functions, and I was close to solve it, and you'll see that names are 
indeed again pretty obvious, but until you grasp this target as a whole 
you don't really realise what is going on. 
I was confused always by X buffering, coz graphic events are not 
implemented immediately, and 5 or 6 buttons from the toolbar 
were painted all together at once.

After one day of useless testing I decided to act methodically, and after 
starting from one obvious point, reach the code I was seeking. I just wanted 
to locate where the button was disabled and then, from there, trace back: 
Reverse Engineering as we have all learned it. 
I studied some Xwindows API, and I got information about events. 
For fixing the problem of  graphic buffered events I read the main page 
of X server:

"All  applications written with the X Toolkit Intrinsics automatically 
accept the following options:
       This  option indicates that requests to the X server should
       be sent synchronously, instead of asynchronously.  
       Since Xlib normally buffers requests to the
       server, errors do not  necessarily  get  reported immediately 
       after they occur.  This option turns off the buffering so that
       the application can be debugged.  It should never be used
       with a working program."
So from now on run: acrobat -synchronous
Perfect, now I had to find the X call. I didn't find the function I was
looking for, so I decided to start from one solid function and then 
test the calling tree until the target function was found. 
This seemed to be a very solid function:


How do I get this name ? Well, as I told you I looked for names about
ToolBar, one of the most suspicious is UnixToolBarUpdateButtonStates, 
which is called from AVAppSelectLegalTool.

One tip that will be useful in X debugging: I found a bug (I don't know if it 
is a gdb problem or X server problem or window manager prob) when you break the 
program and is busy with certain graphic interface task, focus cannot be 
successfully returned to xxgdb, and all X applications freezes. In that case you 
just need to open a new virtual console and kill xxgdb process (and then 
restart it). If you want to prevent this situation, you must break the program 
in some previous "safe" instruction (probably inside another function) with no 
focus-back problem. Then xxgdb will get the focus and when you restart execution 
("cont" command) focus will not be back to acrobat (it will be in background) 
and you can safely break inside that "dangerous code". I am telling you this 
right now because the beginning of this function will be ok as a safe breakpoint 
in our goal of finding out who shades and disables the text button.

Now here's an schematic of AVAppSelectLegalTool:

0x806ccc0 AVAppSelectLegalTool
  AVAppGetActiveDoc         (1 parameter)
  ToolIsEnabled             (7 parameters)
  AVAppSetActiveTool        (7 parameters)
0x806cd19 end

Very cool names but nothing else. After some hours the only fact is that
buttons were updated (BTW for the first time if no protection, and if
protected, they were just "rewritten"; in that case, "clean" the window
covering it, or changing the desktop) in AVToolBarUpdateButtonStates. For
this searching task temporary breakpoints are really useful to use, you 
know, use and throw away breakpoints. 
For example writing this will do it:

(xxgdb)br *AVAppSelectLegalTool 
  ... do something like load some pdf evil file. It will break
(xxgdb)tbr *AvAppGetActiveTool

  ... a temp. breakpoint is set. Now you can see what happen while
  ... AVAppGetActiveDoc is being executed. It breaks at AvAppGetActiveTool
(xxgdb)tbr *ToolIsEnabled

... and so on. You dig it ?

Ok, let's go down to AVToolBarUpdateButtonStates. Here is the good stuff:

  080bbf7 AVToolBarUpdateButtonStates
  080bbfa0  call   *%ebx
  080bbfb3  call   08038ed8 <_init+2168>
or if you want

  080bbf7 AVToolBarUpdateButtonStates
  080bbfa0 call UnixEnumChildWidget
  080bbfb3 call ASListEnum
Be sure that the first function makes what we are looking for. If you watch
the listing of that function it just makes an indirect call to a VERY
important function named SetStateEnumProc. Here is the code commented:

0805ecf0  pushl  %ebp
0805ecf1  movl   %esp,%ebp
0805ecf3  subl   $0x8,%esp
0805ecf6  pushl  %ebx
0805ecf7  movl   0x8(%ebp),%eax
0805ecfa  movl   0x4(%eax),%edx
0805ecfd  movb   0x14(%edx),%al
0805ed00  andb   $0x8,%al
0805ed02  testb  %al,%al
0805ed04  jne    0805ed10 
0805ed06  jmp    0805ed70 
0805ed08  nop    
0805ed0f  nop    

Referenced from jump/call at 0805ed04 ; 

0805ed10  movl   0x8(%ebp),%eax
0805ed13  movl   %eax,0xfffffff8(%ebp)
0805ed16  movl   $0x0,0xfffffffc(%ebp)

Referenced from jump/call at 0805ed63 ;    <LOOPING HERE

0805ed1d  movl   0xfffffff8(%ebp),%eax: 
0805ed20  movl   0xfffffffc(%ebp),%edx;   <<WE CONTINUE HERE !!
0805ed30  movl   0x10(%ebp),%eax; << LOAD SOMETHING
0805ed33  pushl  %eax;                    << SAVE IT
0805ed34  movl   0xfffffff8(%ebp),%eax; << LOAD SOMETHING
0805ed37  movl   0xfffffffc(%ebp),%edx;     << LOAD INDEX
0805ed3a  movl   %edx,%ecx;       << MOVING INDEX TO ECX
0805ed3c  leal   0x0(,%ecx,4),%edx; << CREATE POINTER IN EDX
0805ed43  movl   0x74(%eax),%eax; << LOAD SECOND INDEX
0805ed46  movl   (%eax,%edx,1),%edx;<< DOUBLE INDEXING HERE
0805ed49  pushl  %edx;          <SAVE VALUE
0805ed4a  movl   0xc(%ebp),%ebx; << LOAD FUNCTION ADDRESS
0805ed4d  call   *%ebx;          <<CALL SetStateEnumProc
0805ed4f  addl   $0x8,%esp,          << RETURNS IN EAX 
0805ed52  movb   %al,%al
0805ed54  testb  %al,%al
0805ed56  jne    0805ed60;  << JUMPING BELOW IF RETURNED != 0
0805ed58  jmp    0805ed70;  << ELSE JUMP TO END FUNCTION
0805ed5a  nop    
0805ed5c  nop    

Referenced from jump/call at 0805ed56 ; 

0805ed60  incl   0xfffffffc(%ebp); << INCREMENT POINTER
0805ed63  jmp    0805ed1d;    << LOOP AWAY

One call to SetStateEnumProc for each button. For the first time, we got 
some 'action' (we still don't know which) for a particular button. I don't 
like essays that carry a too heavy listing, so here is the schematic of the 
function and I shall give you afterwards the needed details:

0805aec0 SetStateEnumProc
  call XtVaGetValues
  call AVToolButtonIsSeparator
  call AVToolButtonIsEnabled
  call XtSetSensitive
  call XtIsSubclass    
  call AVToolButtonIsMarked
  call XacroToolButtonSetMarked

XtSetSensitive IS OUR FUNCTION. It enables or disables buttons. If we look
for in the API:

extern void XtSetSensitive(
    Widget              /* widget */,
    _XtBoolean          /* sensitive */
Hence we are interested in the second parameter, that is pushed in the first
place. Some assembler details of the function:

Reference to function : AVToolButtonIsEnabled

0805aef4  call   080bb3a0; << returns 1 or 0 into eax
0805aef9  addl   $0x4,%esp
0805aefc  movl   %eax,%eax
0805aefe  movzwl %ax,%edx; << returned value in edx now
0805af01  pushl  %edx;  << here is our parameter ****
0805af02  movl   0x8(%ebp),%eax
0805af05  pushl  %eax

Reference to function : XtSetSensitive

0805af06<SetStateEnumProc+46> call   08037dc8 <_init+1058>

Now you understand what I told you about zen and luck. If I would listen to
that function ... (actually I had played with it before, but acrobat was in
its asynchronous behaviour and I was confused, you know life is tough). So
this function is  the judge that sort good and evil buttons. This is the
*hot* part of the function :

AVToolButtonIsEnabled       (... bad instructions for your health ...)

080bb43a  call   *%ebx      << this indirect call is calling StdComputeEnabledSelChange
                            << the returned value is saved in eax as usual
080bb43c  addl   $0x4,%esp
080bb43f  movl   %eax,%eax;             << I don't understand it
080bb441  movw   %ax,0xfffffffe(%ebp);  << save the boolean value
080bb445  addl   $0xfffffff8,0x820b904
080bb44c  jmp    080bb45d;               << jumping
080bb44e  nop    
080bb44f  nop    

Referenced from jump/call at 080bb42b ; 

080bb450  addl   $0xfffffff8,0x820b904
080bb457  movw   $0x0,0xfffffffe(%ebp)

Referenced from jump/call at 080bb44c ;   <we are jumping here !!!
080bb45d  pushl  $0x0

Reference to function : AVAppSetBusy

080bb45f  call   080700f0 <AVAppSetBusy>;  <<bla bla bla
080bb464  addl   $0x4,%esp

Referenced from jump/call at 080bb3dd ; 080bb3f2 ; 

080bb467  movw   0xfffffffe(%ebp),%ax;  << move to eax the boolean value
080bb46b  movzwl %ax,%edx;             << more stupid instructions
080bb46e  movl   %edx,%eax
080bb470  jmp    080bb480;            << jump to end
Don't worry this is not endless, we are close to the crack, but we must go to
this "academic" function StdComputeEnabledSelChange. BTW, you may see that
this function has one parameter. For any button but "text-button" the
parameter saved is 0, and for the evil button the parameter is 0x10. Now
you'll see how everything makes sense:

080baef0 StdComputeEnabledSelChange

(... bla bla bla ...)
080baf22  movl   0x8(%ebp),%eax;    << take the parameter
080baf25  pushl  %eax;              << forward the parameter
080baf26  movl   0xfffffffc(%ebp),%eax; 
080baf29  pushl  %eax;              << save another parameter

Reference to function : AVDocCheckPermission

080baf2a  call   0807c8f0 <AVDocCheckPermission>

And last but not least (don't forget the parameter of the first push):

(... bla bla bla ...)
Reference to function : AVDocGetPDDoc
0807c944  call   0807ca90 << get pointer in eax of some pdf structure
0807c949  addl   $0x4,%esp
0807c94c  movl   %eax,%eax
0807c94e  pushl  %eax:  << save pointer

Reference to function : PDDocGetPermissions
0807c94f  call   08038828 <_init+1ab8>      << this function returns en eax the permis. word
0807c954  addl   $0x4,%esp
0807c957  movl   %eax,%eax
0807c959  movl   %eax,%edx   << copy permissions to edx
0807c95b  andl   0xc(%ebp),%edx; << AND with the parameter !!!!
0807c95e  cmpl   %edx,0xc(%ebp)
0807c961  sete   %al
0807c964  movzbl %al,%edx
0807c967  movl   %edx,%eax
0807c969  jmp    0807c970 
0807c96b  nop    
0807c96c  nop    
0807c96d  nop    
0807c96e  nop    
0807c96f  nop    

Referenced from jump/call at 0807c93d ; 0807c969 ; 
0807c970  movl   %ebp,%esp
0807c972  popl   %ebp
0807c973  ret   

We are at the end of our long way. The permission word for an unprotected
document is 0x7fff (rather curious :-). 

For an explanation of this 7FF, check +Zer0's essay:
Actually the value has been transformed a bit high order byte to 7F 
and low order byte incremented by 1 so the desired value at this position 
is 7FFD instead of FFFC. 
You may realise that PDDocGetPermissions is not inside acroread. It is an imported function. The code is located in a library (Acrobat/Reader/intellinux/lib/ You can disassemble it (I'm not gonna punish you any more inside this essay :-) and the function just returns the input parameter+0x78, hence the offset of the permission is 0x78. Now you can crack it any way you want. You may patch the library, overwrite some nops. If you are working with xxgdb I propose you patch quietly AVDocGetPDDoc, and not only return the pointer but "initialise" permissions. These are the commands: (xxgdb)br *0807cac3 (the ret point of the function AVDocGetPDDoc) (xxgdb)commands >silent >set *($eax+0x78)=0x7fff >cont >end There are a lot of things to do (delving into permission word, encryption routines, ...) but you will allow me not to do them right now. I hope this essay will help you with the Windoze version, or at least will help you if you are up to crack some other linux commercial application. For this particular crack I would like to thank Quine for his obstination. Regards also to all +HCUkers and all other friends. "Long is the way and hard, that out of Hell leads up to the light"
(c) SiuL+Hacky 1997. All rights reversed
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