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HOW TO CRACK DLL

This is a discussion on HOW TO CRACK DLL within the Soldier Front Hacks, Bots, Cheats & Exploits forum part of the Soldier Front category; Introduction Lately more and more programs come out that are programmed in VB. Since VB programs are still unknown material ...

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Old 11-14-2010, 08:23   #1
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HOW TO CRACK DLL


Introduction

Lately more and more programs come out that are programmed in VB.
Since VB programs are still unknown material for most crackers they
ignore them and label it as 'uncrackable'. In this document i will
show you that that is not true for text based protections
(serials/reg#'s).

For tools we will need only soft-ice and in one case hiew.
Further-more i assume that the reader is somewhat familiar with
cracking. For absolutely beginners i recommend the great tutorials
made by +orc and ed!son's good windows tutorial. But i will try my
best to make the text understandable for everyone who has a litle
knownledge about cracking.

Getting ourselves prepared

Before i start bombing you with asm listings lets take a moment to
think about what we are dealing with.
We are dealing with exe's that dont have code themselves but instead
they make calls to a library with standard functions.
What does this mean? It means that this is a big disadventage to
protect programs written in VB. Why? Do you think that the writers of
the VB dll made 10 different functions that you can use to compare 2
strings? No, ofcourse not. They made the dll to be as efficient as
possible, as small as possible.

So therefore a good guess is that there will be only 1 or 2 places in
the dll where it can compare two strings. And that turns out to be the
case as you will see if you finish reading this document.

Does the litle lamp already begin to glow in your head ? ;--)
Wouldnt it be great if we knew where in the dll 2 strings get
compared? Yes, it would be great. It would reduce VB cracking to a
boring job of setting a single breakpoint at the right place. Continue
reading for the details.

Strategy

Before we continue it would be wise to set out a strategy (like its
the case with every other case of cracking).

Lets think about the protection ...
You enter a string of text , you hit enter or press 'OK' or whatever.
Then windows gives the data you entered to the VB dll. The VB dll then
does whatever it needs to know if that data is right or wrong. And you
get a msg saying you entered a good/wrong code.
So what would be the weak link in the chain? The answer is where
windows gives the data you entered to the VB dll. Thats our entry
point. We can make softice break there. And then we are at the source
of the protection-chain. With the aid of breakpoints we can then
monitor what happens with our text.

I think that we now have enough background information to crack a
first example.

Case 1 : The Collector v2.1

The collector is an utility for creating and maintaining your
image/photo collection. Not bad for a VB program.

More info about this program :

Name : The Collector v2.1
Where : [Only registered and activated users can see links. ]
Size : collectr.exe = 246.047 bytes
Protection : serial
DLL : uses VB3 dll

I find it easier to explain things in steps. So therefor i will split
the cracking process in smaller chunks :

Step 1 : Run The Collector - right at startup it will ask you for a
serial #

Step 2 : Enter a dummy serial like '9876543210'. Now press control-d
to enter softice. In softice enter 'bpx hmemcpy' to place a breakpoint
on the hmemcpy function of the kernel.

Intermezzo : What is hmemcpy ?
Windows uses hmemcpy alot in operations concerning strings. In this
case it will be used to copy the buffer with the text we entered to
the memory space of the VB dll. Remember when i said that we were
gonna break when windows gave the string we entered to the VB dll?)

Step 3 : Leave softice with control-d. And press 'OK". This will make
softice break right at the beginning of hmemcpy.

Step 4 : Now we will continue with tracing further into the hmemcpy
function to find out where the string we entered will be stored. Keep
pressing F10 untill you see this :

JMP 9E9F
PUSH ECX ;these lines copy the
SHR ECX,02 ;string at ds:si to es:di
REPZ MOVSD
POP ECX
AND ECX,03
REPZ MOVSB
XOR DX,DX

Step 5: Right before REPZ MOVSD do a 'ed si'. You will the text you
entered, in my case its shows '0987654321'. Do a 'ed es:di' and you
will see nothing (yet). But if you press F10 and get passed the REPZ
MOVSB you will see the text getting copied to this new location where
the VB dll can access it.

Step 6: Now we know where the text is located. Lets review our
strategy here. Our plan was to find out where the VB dll kept our
serial, then put a breakpoint on that memory location and find out
with what it got compared. So, lets set a bpr (breakpoint on range) at
the location with our string. Since the REPZ MOVS(D/B) instructions
increased the pointer in di (it now points to the end of our string)
we do 'bpr es:di-8 es:di-1 rw'. Dont hit enter yet - read step 7
first.

Step 7: Before you hit enter i will tell you what to expect. Softice
will break everywhere where that block of memory with the string is
read or written to.

For example you will break inside the function strlen where the lenght
of the string is calculated.
And you will break where the string is copied to another place in
memory (for example with REPZ MOVSW). When this happens place a new
bpr at the new location with the string.
It will also break when the string or part of it gets deleted. If not
the whole string gets deleted do not remove the corresponding bpr.
Only remove it when the complete string gets written over by something
else.
Also you will break again in hmemcpy. Hmemcpy will read another echo
of the string in the dll's memory. Place a bpr there too.
And finally you will break at the part of the code that does the
comparing (the instruction you will see is REPZ CMPSB).

When i reached that part of code i had 4 breakpoints set. One
breakpoint for hmemcpy and 3 bpr's on 3 echos of the string (or parts
of it).

Step 8: Now we found the code where the VB3 dll does comparing we can
place a breakpoint there and disable the other breakpoints. We wont
need them anymore. We found the place where things get compared in
VB3. What you see is this :

: 8BCA mov cx, dx
: F3A6 repz cmpsb ;<- here the strings in ds:si and es:di
: 7401 je 8CB6 ; are being compared
: 9F lahf
: 92 xchg ax,dx
: 8D5E08 lea bx, [bp+08]
: E80E06 call 92CB

Just before the REPZ CMPSB if you do a 'ed si' and a 'ed es:di', you
will see what is compared with what. In this case the second and third
character of the string we entered gets comared with 'V8'. So if you
restart the program and enter 0V87654321 it will register.

Step 9: We are not finished yet. The contrary is true, the important
part is what we do now. Next time we meet a VB3 program we want to
place a breakpoint at the location with the code above and read out
the right serial.

How do we do that ? Lets try it real quick with The Collector.
* Start The Collector and enter a dummy serial.
* Enter softice and place a breakpoint on hmemcpy.
* Leave softice and press 'OK', this will put you back in softice.
* Now, get out of the kernel and and get in the code of VBRUN300 (press
F11 and F10 untill you get there)
* Now do a search for the pattern :
8B,CA,F3,A6,74,01,9f,92,8D,5E,08,E8,0E,06
:s 0 l ffffffffff 8B,CA,F3,A6,74,01,9f,92,8D,5E,08,E8,0E,06
* Place a breakpoint at the adress that gets returned
:bpx <segffset>
* press F5 and you will land in the middle of the above comparing code.
* Only thing left to do is check out the pointers in es:di and ds:si

Case 2 : Minimize Magic 1.2.4

Minimize Magic is an utility that you can use to minimize your
programs to the traybar.

More info about this program:

Name : Minimize Magic 1.2.4
Where : [Only registered and activated users can see links. ]
Size : minimagic.exe = 159.744 bytes
Protection : password based on key
DLL : uses VB4 dll

To crack this program you can do the same as we did with The
Collector. Starting with hmemcpy working your way to the code that
compares the string you entered. Important thing to know is that the
VB4 dll always converts strings to the WideChar format before it does
anything with them. So instead of using hmemcpy you can set a
breakpoint on MultiByteToWideChar to break. Check your windows API
reference to learn more about this function.

I have done all the hard work for you and found the VB4 dll code that
compares two strings (in WideChar format !).

Heres the listing :

: 56 push esi
: 57 push edi
: 8B7C2410 mov edi, [esp + 10]
: 8B74240C mov esi, [esp + 0C]
: 8B4C2414 mov ecx, [esp + 14]
: 33C0 xor eax, eax
: F366A7 repz cmpsw ;<-- here the (WideChar) strings at ds:esi
: 7405 je 0F79B362 ; and es:edi get compared
: 1BC0 sbb eax, eax
: 83D8FF sbb eax, FFFFFFFF
: 5F pop edi
: 5E pop esi
: C20C00 ret 000C

Now we know enough of the VB4 dll to crack Minimize Magic:

Step 1: Start Minimize Magic and chose Register from the menus. You
will be asked for a Name and a Password. Enter a name and a dummy
password. Dont press 'OK' yet, continue with next step.

Step 2: Enter softice and place a breakpoint on hmemcpy. Leave softice
and press 'OK'. You will land in softice.

Step 3: Press F11 and F10 untill you are out of the kernel and in the
code of the VB40032.dll. Now we will search for the pattern of the
code above. Do 's 0 l fffffffff
56,57,8b,7c,24,10,8b,74,24,0c,8b,4c,24,14' and place a breakpoint at
the adress that gets returned.

Step 4: Press F5 to leave softice, but you will immediately break
again, right at the beginning of the above code. Here the password you
entered will be compared to the correct password. Trace untill right
before the REPZ CMPSW and do 'ed es:edi', this will show the password
you entered. If you do 'ed esi' you will see the correct password.
(the strings will be in WideChar format - for example you could see A
T G H D E H D. That means your password is ATGHDEHD)

Ok, now you found a working password that will work only for the
version on your computer. If you give that password to somebody else,
the program wont accept it. The password is calculated from a Key that
is different on each computer. This key could be randomly generated at
setup or based on the info on your hd. Whichever one it is, it will be
hard to find out how its generated or where it is stored.

So how can we make a general crack ?

We could use the 'Magic Window' trick here. We will 'reprogram' the
VB40032.dll to show the correct password.

The original code in the VB40032.dll looks like this :

:0F79B348 56 push esi
:0F79B349 57 push edi
:0F79B34A 8B7C2410 mov edi, [esp + 10] ; es:edi -> pw you entered
:0F79B34E 8B74240C mov esi, [esp + 0C] ; esi -> correct pw
:0F79B352 8B4C2414 mov ecx, [esp + 14]
:0F79B356 33C0 xor eax, eax
:0F79B358 F366A7 repz cmpsw ; compare them
:0F79B35B 7405 je 0F79B362
:0F79B35D 1BC0 sbb eax, eax
:0F79B35F 83D8FF sbb eax, FFFFFFFF
:0F79B362 5F pop edi
:0F79B363 5E pop esi
:0F79B364 C20C00 ret 000C ; end of this function
:0F79B367 57 push edi ; the code below this adress
:0F79B368 8B7C2408 mov edi, [esp + 08] ; is not important, but we
:0F79B36C 8B4C2410 mov ecx, [esp + 10] ; will need its space
:0F79B370 8B44240C mov eax, [esp + 0C]
:0F79B374 0BE4 or esp, esp
:0F79B376 F266AF repnz scasw
:0F79B379 B800000000 mov eax, 00000000
:0F79B37E 7503 jne 0F79B383
:0F79B380 8D47FE lea eax, [edi-02]
:0F79B383 5F pop edi
:0F79B384 C20C00 ret 000C

The code is located at offset 7a748 in the vb40032.dll file. So, to
make a general crack make a patch that turns the above code into:

:0F79B348 56 push esi
:0F79B349 57 push edi
:0F79B34a 8B7C2410 mov edi, [esp + 10] ;es:edi --> text you enter
:0F79B34E 8B74240C mov esi, [esp + 0C] ;esi --> correct pw
:0F79B352 813F70006300 cmp dword ptr [edi], 00630070 ;edi -> 'PC" ?
:0F79B358 7527 jne 0F79B381 ;if not - leave
:0F79B35A 803E00 cmp byte ptr [esi], 00 |<- these lines
:0F79B35D 7410 je 0F79B36F | put spaces
:0F79B35F 83C601 add esi, 00000001 | between the chars
:0F79B362 C60620 mov byte ptr [esi], 20 |
:0F79B365 EB03 jmp 0F79B36A |<--skip the ret
:0F79B367 C20C00 ret 000C ;<-- this to prevent crash
:0F79B36A 83C601 add esi, 00000001 |
:0F79B36D EBEB jmp 0F79B35A |<- back to the start
:0F79B36F 8B3DDCC47B0F mov edi, [0F7BC4DC] *<-- these lines
:0F79B375 8B74240C mov esi, [esp + 0C] * call the
:0F79B379 6A00 push 00000000 * MessageBoxA
:0F79B37B 56 push esi * function to show
:0F79B37C 56 push esi * the correct
:0F79B37D 6A00 push 00000000 * password
:0F79B37F FFD7 call edi *
:0F79B381 5F pop edi
:0F79B382 5E pop esi
:0F79B383 90 nop
:0F79B384 C20C00 ret 000C

Comments:

We used the space of two routines, so to prevent a crash we have to
put a RET function at the beginning of the (original) second function
(see line 0F79B367).

This part of the VB4 dll code is not only used to check the passwords.
It is used by other parts of the program as well. Therefor we need to
do something so that only something will be shown when we are dealing
with a password comparison. That is what the code at line 0F79B352 is
about. It checks to see if EDI points to the text "PC". So we can use
that to trigger the crack. To trigger the crack, "PC" has to be
entered for password when registering.

The lines marked with | are there to put spaces between chars of the
string. Originally there would be a string of WideChar format. That
means that in memory there will be zero's between the chars. And the
function we will use to show the text (MessageBoxA) translates a 0 to
end of string. So only 1 letter would be shown if we dont replace the
zeros with spaces.

The lines marked with * are there to call the function MessageBoxA to
show the correct password. I ripped those commands from the VB4 dll.
Placed a breakpoint on MessageBoxA to see how VB4 called it.

Well thats it for Minimize Magic. To make a general crack, a patch
could be written that patches the VB4 dll at offset 7a748 with the
above code. To use such a crack minimagic.exe and the vb40032.dll
should be placed in a temp dir and the patch run there. Then start
minimize.exe from that temp dir, and use 'PC' for password. And voila,
a window will pop up with the correct password. Once the correct pw is
known, the temp files should be deleted and the password can be used
in the original Minimize Magic.

Case 3 : Sub Station Alpha 2.02

Most of the VB4 programs can be cracked with the method described in
case 2, but i have encountered 2 programs which used a different
method of comparing. One of those programs is Sub Station Alpha 2.02.
It uses a protection that first converts a number you enter to its hex
value and then compares it with the correct number. Lets start to
crack Sub Station Alpha and things will get clearer.

Info about this program:

Name : Sub Station Alpha 2.02
Where : [Only registered and activated users can see links. ]
Size : SUBSTN32.EXE = 629.248 bytes
Protection : password based on user name
DLL : uses VB4 dll

Earlier i mentioned that VB4 converts strings to the widechar format
before it does aything with them. Therefor we will use this function
as an entry point. Again we will do it step by step ;--)

Step 1: Start Sub Station Alpha and chose register from the menus.
Enter a name and a dummy registration key.

Step 2: Enter softice and place a breakpoint on MultiByteToWideChar
(with 'bpx MultiByteToWideChar')

Step 3: Now, leave softice and press "Register".

Step 4: Softice will break at the beginning of MultiByteToWideChar,
press F11 to get out of it. You will see :

:FF1500C27B0F call [KERNEL32!MultiByteToWideChar]
:8BD8 mov ebx, eax
:83FEFF cmp esi, FFFFFFFF
:7501 jne 0F738BCF
:4B dec ebx
:53 push ebx
:6A00 push 00
:FF1518C97B0F call dword ptr [0F7BC918]
:8BE8 mov ebp, eax
:85ED test ebp, ebp
:0F845B260100 jz 0F74B23D
:43 inc ebx
:53 push ebx
:55 push ebp
:56 push esi
:57 push edi
:6A00 push 00
:6A00 push 00
:FF1500C27B0F call [KERNEL32!MultiByteToWideChar]
:8BC5 mov eax, ebp ;<-- do 'ed ebp' here
:5D pop ebp
:5F pop edi
:5E pop esi

The important place is right after the second call to
MultiByte-ToWideChar. Disable the first bp on MultiByteToWideChar and
place a new bp right after the second call to that function (on the
line with MOV EAX,EBP). On that line EBP will contain a pointer to a
string in WideChar format that was processed. It doesnt have to be the
string of the registration key. Therefor we will edit that breakpoint
so that it will only break when it is processing the registration key.

How can we do that? Well, the MultiByteToWideChar function returns the
lenght of the string it processed plus 1 in EAX. So we will add a
conditional statement on the breakpoint. Do 'bl' to find out what the
number is of that breakpoint. Then do 'bpe #' and add 'if al==' to the
breakpoint. For example, if you entered '212121', lenghtOfKeyString
would be 6 :--).

Step 5: Now we will let the program run with F5. When softice breaks
do a 'ed edp' and see the WideChar form of the key you entered. We
place a bpr on the block of memory containing the string and we
continue (F5). What will happen is this. Softice will break on several
places. Whats important is that it will break in the code of OLEAUT32.
When that happens trace a litle further to see whats going on. The
first few times you will get out of the OLEAUT32 very quickly. But
eventually you will see this code :

( listing from OLEAUT32.DLL)
:6534B6B3 395C240C cmp [esp + 0C], ebx ; this is a loop that
:6534B6B7 7E14 jle 6534B6CD ; goes trough all
:6534B6B9 33C9 xor ecx, ecx ; the chars of a
:6534B6BB 8D0492 lea eax, [edx + 4*edx] ; string, in the end
:6534B6BE 8A0E mov cl , [esi] ; edx will have the
:6534B6C0 46 inc esi ; hex value of the string
:6534B6C1 4F dec edi
:6534B6C2 FF4C240C dec [esp + 0C]
:6534B6C6 8D1441 lea edx, [ecx + 2*eax]
:6534B6C9 85FF test edi, edi
:6534B6CB 7FE6 jg 6534B6B3
:6534B6CD 85FF test edi, edi
:6534B6CF 7F4A jg 6534B71B
.............
.............
:6534B6F2 8910 mov [eax], edx ; edx is saved
:6534B6F4 33C0 xor eax, eax
:6534B6F6 83C424 add esp, 00000024
:6534B6F9 C21000 ret 0010

Step 6: We saw that the key is transformed into its hex value, and
saved to a place in memory. If you monitor this memory location, you
will end up here in the VB4 dll that compares it with another value:

:0F7A2CE1 5A pop edx ; load edx
:0F7A2CE2 58 pop eax ; load eax
:0F7A2CE3 2BC2 sub eax, edx ; subtract them
:0F7A2CE5 83F801 cmp eax, 00000001
:0F7A2CE8 1BC0 sbb eax, eax
:0F7A2CEA 50 push eax
:0F7A2CEB 0FB706 movzx word ptr eax, [esi]
:0F7A2CEE 83C602 add esi, 00000002
:0F7A2CF1 FF2445F4997B0F jmp dword ptr [2*eax + 0F7B99F4]
:0F7A2CF8 E8BB000000 call 0F7A2DB8

We see that EDX and EAX get loaded from the stack, and then
substracted. This is just an indirect way of comparing those two
values. If you check out the contents of EAX and EDX, you will see
that one has the number you entered and the other one will have the
correct registration number.

Step 7: Now we found this location its wise to note the hex values of
the code, so you can find it back quickly when you suspect that
another VB4 program uses this protection.

Final notes

Well, with the above 3 techniques i have been able to crack quite some
VB3/4 programs that used a text based protection. Sometimes when you
set a breakpoint at the comparing routine, softice will not break. Try
then to enter strings with a different length. Because the program
could be checking the length of the string you enter before it
compares the string itself. And other programs first isolate chars
from the string you enter and then compare those isolated chars, but
again they get compared at the locations stated in the examples above.

With VB5 programs i havent much experience, i only cracked one of
them. It was called Hitlist Pro v3.0. By patching the VB5 dll, I could
remove its 30 day timelimit just like it was a regular program. Of
course, the VB5 dll had to be placed in the Hitlist Pro main dir, this
to prevent other VB5 programs using the patched DLL.

Thats it folks, you may contact me (if you know how ;--) on irc with
feedback and questions.

Big greets to : tHATDUDE, madmax!, cH, Teraphy, KillerBee,j0b,
StarDogg Champion,aCP,rANDOM and all the others i forgot.

Special greets and thanks to +ORC, fravia and gthorne and rest of +HCU
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Old 11-14-2010, 08:31   #2
FireEyes and HSzaldy is 1
 
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T_T i wish i can understand what he is saying... im not a prog.. T_T
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Old 11-14-2010, 08:41   #3
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dang! worse than math! *imo* XDDD
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Old 11-14-2010, 08:50   #4
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wew..nosebleed and at the same time brain freeze..i really admire those people who knows how to do this...hats off to you guys..
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Old 11-14-2010, 09:01   #5
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lol how funny cracking dll tutorial was also gettin leeched.. :P This is razzia's tut lol.. anyway I hope people here learns how to understand this. Yes this is worst than math. :P
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Old 11-14-2010, 09:07   #6
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hahah over... we must be a programmer to understand this one ^^

Last edited by toledz; 11-14-2010 at 09:11.
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Old 11-14-2010, 09:21   #7
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Well, speakin' of compilers and sumthin, I have Microsoft Visual Studio C++ here, is it enough to crack DLLs? because if it is, I'll do my own hacks and sumthing
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Old 11-14-2010, 09:23   #8
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IT programmers can understand that. sad to say that i can't understand all of 'em!!!
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Old 11-14-2010, 09:27   #9
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† my decompiler is PE explorer †
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Old 11-14-2010, 10:11   #10
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Nice Thread men, hope other member can understand this.
I hate math, then i also hate this. joke.
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