ARJSHELL DISABLED SAVE FUNCTION

("A location helds the secret")

by Rundus

(26 September 1997)


Courtesy of reverser's page of reverse engineering

Well, an intersting little essay from Rundus, about a save disabled target. Enjoy!

		ARJSHELL DISABLED SAVE FUNCTION
			  by Rundus	
			(20 September 1997)

To begin with I apologise to all my fellow crackers who might find
that my tutorial is too simplified. But I like to use the management
technique KISS ( Keep It Simple Stupid ).

The program is Arjshell verion 1.2 and it can be found at 
http://www.windows95.com
or 
http://www.filez.com  ( arjsh12.zip )

The program is a front end for the popular arj.exe compression program.
The help file states that the save project and dos-batch files function
is disabled. Also the load project files function is disabled.

So loading Arjshl32.exe into Wdasmv89 and opening STfn Ref we find this:

"Sorry, saving projects is possible in registered version only"
"Sorry, saving Dos-batch is possible in registered version only"
"Sorry, loading projects is possible in registered version only"
"You are a registered user of Arjshell"

Double clicking on these and this is what we find:

|:0042F693(C)
|
:0042F702 E87D450000              call 00433C84	:Here
:0042F707 A2D3774300              mov byte ptr [004377D3], al ;Flag good
:0042F70C 803DD377430000          cmp byte ptr [004377D3], 00 ;guy/badguy
:0042F713 747F                    je 0042F794		      ;jump bad guy
:0042F715 8D55FC                  lea edx, dword ptr [ebp-04]
:0042F718 8B83B4010000            mov eax, dword ptr [ebx+000001B4]
:0042F71E E8492CFEFF              call 0041236C
:0042F723 8B45FC                  mov eax, dword ptr [ebp-04]
:0042F726 50                      push eax
:0042F727 33C9                    xor ecx, ecx

* StringData Ref from Code Obj ->"ArjShell\UserName"
                                  |
:0042F729 BA0CF84200              mov edx, 0042F80C
:0042F72E B800000080              mov eax, 80000000
:0042F733 E810BCFFFF              call 0042B348
:0042F738 8D55FC                  lea edx, dword ptr [ebp-04]
:0042F73B 8B83B8010000            mov eax, dword ptr [ebx+000001B8]
:0042F741 E8262CFEFF              call 0041236C
:0042F746 8B45FC                  mov eax, dword ptr [ebp-04]
:0042F749 50                      push eax
:0042F74A 33C9                    xor ecx, ecx

* StringData Ref from Code Obj ->"ArjShell\UserID"
                                  |
:0042F74C BA28F84200              mov edx, 0042F828
:0042F751 B800000080              mov eax, 80000000
:0042F756 E8EDBBFFFF              call 0042B348
:0042F75B B8D0764300              mov eax, 004376D0

* StringData Ref from Code Obj ->"You are a registered User of ArjShell "
                               ->"now !"
                                  |
:0042F760 BA40F84200              mov edx, 0042F840
:0042F765 E89E65FDFF              call 00405D08
:0042F76A 6A40                    push 00000040

* Reference To: user32.MessageBeep, Ord:0000h
                                  |
:0042F76C E83F56FDFF              Call 00404DB0
:0042F771 6A40                    push 00000040

* StringData Ref from Code Obj ->"Registering successful"


	ANOTHER SECTION OF CODE

:00431F02 803DD377430000          cmp byte ptr [004377D3], 00
:00431F09 751D                    jne 00431F28

* StringData Ref from Code Obj ->"Sorry, saving DOS-Files is possible "
                               ->"in the"
                                  |
:00431F0B 6848214300              push 00432148

* StringData Ref from Code Obj ->"Warning"


	ANOTHER SECTION OF CODE

:00432EF2 803DD377430000          cmp byte ptr [004377D3], 00
:00432EF9 751D                    jne 00432F18

* StringData Ref from Code Obj ->"Sorry, loading Projects is possible "
                               ->"in the"
                                  |
:00432EFB 6804364300              push 00433604

* Possible StringData Ref from Code Obj ->"Warning"

	ANOTHER SECTION OF CODE

* Referenced by a Jump at Address:004322C2(C)
|
:00432338 803DD377430000          cmp byte ptr [004377D3], 00
:0043233F 751D                    jne 0043235E

* StringData Ref from Code Obj ->"Sorry, saving Projects is possible "
                               ->"in the"
                                  |
:00432341 68EC2A4300              push 00432AEC

* StringData Ref from Code Obj ->"Warning"


Well as you can see, everthing is controlled by the flag [004377D3]
and it is set by the value in AL. So lets have a look at what is inside
call 00433C84
Hmm, its quite long and too many other calls and jumps. So lets use
softice.

:0042F702 E87D450000              call 00433C84	;Here
:0042F707 A2D3774300              mov byte ptr [004377D3], al
:0042F70C 803DD377430000          cmp byte ptr [004377D3], 00

(1) Run the program Arjshl32.exe and goto Preferences,then Register.
(2) Enter in name and bogus serial number.
(3) control D   ^D  inside softice v3
(4) :bpx hmemcpy   ;set breakpoint on copying what we have entered in.
(5) :bpm 004377D3 w ;breakpoint on memory location.
(6) hit F5 key twice
	
Ok, we are now here.Your segment address might be different, but offset
will be the same (????:0042F707).

014F:0042F702         call 00433C84	
014F:0042F707         mov byte ptr [004377D3], al
014F:0042F70C         cmp byte ptr [004377D3], 00

(7) :bc *	;clear all breakpoints
(8) :bpx 014F:0042F702  ;breakpoint for call routine.
(9) Hit F5 key,back to program and then Reregister.
(10)Back inside softice, hit F8 key ;to trace inside call routine.
(11)Hit F10 key ;until you come to this code (35 times in my case).

:00433CF2 E931F3FCFF              jmp 00403028
:00433CF7 EBEB                    jmp 00433CE4
:00433CF9 8BC3                    mov eax, ebx
:00433CFB 5F                      pop edi
:00433CFC 5E                      pop esi
:00433CFD 5B                      pop ebx
:00433CFE 8BE5                    mov esp, ebp
:00433D00 5D                      pop ebp
:00433D01 C3                      ret

I always set my code window for 7 lines  :wc 7

At offset address :00433CF9 eax has 0000 moved into it.So we now need to
change this instruction and we only have two bytes.
Can't use mov eax,0001 (B801000000). Ok,change to mov al,01 (B001)

For a manual on opcodes try the one at
http://www/expage.com/page/w32dasm

The only thing to complete is to load Arjshl32.exe into your Hex Editor
and make the changes. 

Now the save and load functions will be enabled. But you will not be
able to register because the register button is disabled.
This doesn't matter because the username is not displayed anywhere and 
the program still works after 30 days. 

I have changed the value of ebx from 00000000 to 00000001 on the fly and
the only other thing it seems to do is make two new keys UserName and
UserID in the register at HKEY-LOCAL-MACHINE\Software\Classes\Arjshell
The only thing I can think of is that the program uses the section of
code, that contains the modified instruction to check if the program is
registered. 
Hmm... interesting! 
Maybe I will look at it again, sometime in the future and 
check to see where the register button is disabled.

For those who dont know how to edit registers on the fly do the
following:
(1) Hit the F10 key until you are one instruction before the 
    MOV EAX, EBX instruction
(2) :r ebx	;to edit the register
(3) Change 00000000 to 00000001
(4) Hit Esc button

Well, I am sure that one of my fellow crackers will be able to find 
a better solution than mine... please be my guest!  
(maybe Reverser will include it as a compare... I would welcome it :-) 

That's all for now and I hope someone finds my tutorial useful.

cheers Rundus   
(c) Rundus 1997. All rights reversed
You are deep inside reverser's page of reverse engineering, choose your way out:

redBack to project 6
redhomepage redlinks redanonymity +ORC redstudents' essays redacademy database
redtools redcocktails redantismut CGI-scripts redsearch_forms redmail_fravia
redIs reverse engineering legal?