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+ORC Cracking Lesson 1: An approach to cracking

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· 5 years ago

The best way to learn cracking (i.e. understanding, broadly individuating, locating exactly and eliminating or suspending or deferring one or more protection schemes inside a software application you do not possess the source code of) is to begin your tampering experiments using OLDER applications which have OLDER protection schemes.

In this way you 'll quickly grasp the base techniques of the trade. Do not forget that the evolution of the protection schemes has not been a one way road... strictly speaking it's not even an evolution: you'll eventually find some very clever new tricks, but most of the time you 'll unearth only various trite repetitions of past (and well known) tricks. This is no wonder: the REAL knowledge of the "commercial" programmers themselves (the "protectionists") is often very limited indeed: they are inclined to use the old methods (albeit somehow changed, sometimes even improved) instead of conceiving new methods. This typical "commercial" degeneration happens every time people act for money instead of doing things for the sake of it or for pleasure. This "commercial" trend is blindly encouraged by the stupid, money-oriented society we are coerced to live in.

So I'll begin the "hands on" part (-> starting from lesson 3), using as examples, some "old" applications and some "old" tricks. We'll be able to come later over to the newest protection schemes in order to understand them, and you 'll learn how to defeat this kind of junk too. I'll also explain WHERE you can find a lot of programs to crack for next to no money at all, and HOW 'grossomodo', you should proceed in your work.

This tutorial is for people who are getting started with cracking. Maybe you are just contemplating doing some cracking, maybe you have tried it with mixed success. If you are here to get aimed in the right direction, to get off to a good start with the cracking tricks and procedures, then you have come for the right reason. I can't promise you'll get what you want, but I'll do my best. On the other hand, if you have already turned out some working cracking code in assembler and already cracked many different protection schemes, then this tutorial is likely to be on the elementary side for you. (If you want to review a few basics and have no where else pressing to go, then by all means stay).

In order to crack successfully you need four basic things:

A passing knowledge of assembler language (the more you know, the better and quicker you crack)
Some intuition
Some help from more experienced cracker
A non mercantile mind (more about this later)

The applications you'll use to learn with can be divided into:

Password crippled applications (the easiest to crack)
applications crippled on how many times, or how many days, you use them (fairly easy to crack)
applications crippled on which date you use them before (easy to crack)
applications that have some functions present but disabled (sometimes easy, sometimes difficult)
applications crippled on Disk access (protections schemes that are now defined as "obsolete") and applications crippled on CD-ROM presence (more or less the same methods, but -somehow- not defined as "obsolete") (very easy to crack)
CRYPTOGRAFED ADDS ON (i.e. one of the previous protection schemes, but with some scrambled or self modifying code (XORring and SHRLing codes)or peppered with "junk" instructions (fairly easy to crack)
None of the above (sometimes difficult to crack)

WHERE TO GET THE STUFF

The recent widespread appearance of "Demo"-CDROM on magazine covers is a treasure for all crackers! A short time after their release you 'll get all the copies that remain unsold for next to free. The demos on CD-ROMs will permit you to gather quickly a lot of applications -old and new- that have somehow been crippled (at times with interesting schemes). Truly a wonderful world of cracking possibilities! Gee! For next to no money you can secure on one CDROM the whole of LOTUS applications (or Microsoft or Wordperfect, or you name them) on "trial for 30 days" or "try it 20 times" editions. You'll really enjoy to crack them, to use them for ever and ever and/or graciously donate them on the Web to the poor lamers that have no money and no brain.

GAMES are definitely not to be frowned upon! They are very interesting from a cracker prospective coz they are often "overprotected". With this I mean that they possess protection schemes of a relatively HIGH level hidden inside files that are relatively small. Now, see, it is much more easy, and simple, to track down and eliminate protection schemes inside a single 35.000 bytes long executable file than to locate them inside a collection of many lengthy DLLs and overlaids that could have swollen as long as 2.000.000 bytes each. The lazy bunch of "modern" programmers relies systematically for protection schemes on this "hide the sting in the wide desert" logic. As a matter of fact they are no longer able to program in assembler: they bank more and more on overbloated "fatty" atrocities like Visual Basic, Delphy or Visual C++. (Don't worry... I'll nevertheless teach you how to crack -and quickly- those huge applications too).

There is another reason for employing games instead of applications as study material: often EXACTLY THE SAME protection schemes that you find in a simple (and short) shareware game will be used -without much improving- a little later in order to "protect" some huge and extremely expensive graphic application.

For this reason in my tutorial we'll often crack games protection schemes, even if we'll later apply what we learn mainly in order to crack the protection schemes of commercial applications, or to crack the access protection routines to remote servers, or BBS, or even ATM (cash dispensers).

Here follows an example cracking session, that will show you -I hope- the dos and donts of our art: let's crack together as introductory example a time crippled application. We'll learn later (-> LESSON 4) that all applications that are crippled on time (i.e. "how many times" you use them or "how long" you use them) rely on analogous protection schemes (albeit with a huge palette of small variations):

they may have a counter which "clicks" every so often: FIND IT AND DISABLE IT!
they may fetch the time_clock interrupts in your machine: INTERCEPT THEM YOURSELF!
they may compare a random_seed with a variable: NOOP IT!
they may check randomly the date of your other, unrelated, files on the hard disk: find this verification routine and INVERT the JUMPS!

I wanted to start with a modern example of this "counter clicks" protection type, just to give you a feeling for cracking, and I have chosen a widely published demo: you should be able to find it pretty easily. In order to show you some of the problems you may encounter we'll crack this example "wrongly" (you'll learn how to crack effectively in the "HANDS ON" lessons).

EXAMPLE: ARCADE POOL, Demonstration version, PC Conversion by East Point Software Ltd, (c) Team 17 Software Ltd 1994. This demo has been published by many magazines on their CDRom covers throughout 1995.

What follows will be useful even if you do not have our example; nevertheless you should get a copy of this widespread demo in order to better grasp some of the following points.

This nice demo of a billiard game is time-crippled. It is crippled on how long you use it: i.e., you can only play 2 minutes, afterwards a "nag" reminder of where and how you can buy the real version snaps: protectionist squalor at its best.

So, how do you proceed? Where does the beginning begin? Here is what you could (but not necessarily should) do:

Get [Soft-ice] and load it in your config.sys. See the TOOLS OF THE TRADE lesson (-> LESSON 2) about this debugger. Version 2.6 of [Soft-Ice] has been cracked by MARQUIS DE SOIREE and can be found on the Web for free.

vecs s (save all the vectors before loading the babe)
start [pooldemo.exe]
vecs c(vector compare, save a printing of all hooked vectors)
enter and leave Soft-ice a few times to understand what's going on and where in [pooldemo.exe] are we roaming around (you should always check MORE THAN ONCE your findings when you snoop around: nothing moves and confuses pointers in a more frenzied way than good old "inactive" DOS).
have a good look at the map of memory usage ("map")
now "snap_save" the main memory regions where [pooldemo.exe] dwells... snapping saves "photographs" of memory areas.
do not do anything, let just the seconds go by.
"snap_compare" every two or three seconds without moving anything at all on the game board (no mouse_clicking, NOTHING), so that the only changes are (hopefully) the changes caused by the time counters.
snap_compare twice in a second.
snap_compare at second 00:59 and at second 1:01.
snap_compare just before and just after the time limit and the snapping of the nag screen.
Now collect carefully your printed "snaps" data: write clearly on the various sheets the occurrences of the snaps.
now comes the graceful "zen-cracking" moment: Sit down with a dry Martini and Wodka (obviously only russian Wodka will do) and contemplate the printing of the various mutant locations. Feel, perceive, empathize! Look closely at the locations that have changed in the snap compares. Analyze, interpretate, evaluate.
Mmm! Hey! Something fishy is changing there, and there, and there! (you are lucky, few do actually change in this case: only two dozen)
breakpoint on execute at the location that you believe act as a "continuous" counter, i.e. the location that triggers the "a second went by" event when it zeroes.
Now set the occurrence counter of BPX in order to break at the moment where the location "refills" and restarts from the beginning (the equivalent of "one second" went by, let's start anew). Use the occurrence counter in order not to single-step through the program your life long!
IN THIS CASE you 'll quickly locate the refill at location 3DD0. Here follows the "refill" line: xxxx:3DCC C706F1013C00 MOV WORD PTR [01F1], 003C

The "3C" byte at xxxx:3DD0 represents a counter_byte... i.e. the program "charges" 3C in this location and then DECs it step by step to 3B, 3A, 39, 38 etc... till 0. When it reaches 0: bingo! Sucker user has lost one second more of his precious two minutes.

Now, you would get a first wizard level if you searched further on for the exact point where you get the "nag screen" in order to eliminate the whole witless protection, but you may think you got it already and you remember anyway that the first principle in cracking is the following: "once you can eliminate the effects of a protection, do not look further!"

Most of the time this is true: you do not always need to eliminate a "whole" protection scheme (unless you are just studying it for the joy of it). It's normally easier (and quicker) to eliminate the "effects" of a given protection scheme. Unfortunately this is not true in this case.

Here you believe that you have already found the way: you got the counter that charges the reverse clock that triggers the particular protection scheme of [pooldemo.exe]. Now you may think that if you could modify the refill_value... say changing "3C" to "EE" (Yeah, the maximum would be FF... but it's always good practice to avoid such extreme values when cracking) you should get four times more playtime for your game... more than enough in order to make the protection scheme useless.

So you change location xxxx:3DD0 from "3C" to "EE". To work on bytes you should use a good Hexeditor like PSEDIT (Parity solutions, [Psedit.exe], brilliant shareware: see the "tool of the trade" section) but you could also work with simpler debuggers like [debug] or [symdeb] (-> see lesson 2). If you do, remember to work on a "dead" copy of your crippled [*.exe] file, i.e.:

     ren POOLDEMO.EXE POOLDEMO.DED 
     symdeb POOLDEMO.DED 
     -s (cs+0000):0 Lffff C7 06 F1 01 3C <-  this string 
                                             corresponds to the 
                                             refill line). 
     cs:3E85   <- symdeb gives you two locations as answer 
     cs:3EEA 
     -e cs:3E85+4 EE     <- refill changed from 3C to EE 
     -w 
     ren POOLDEMO.DED POOLDEMO.EXE

Now you run your tampered pooldemo. You think you cracked it, you glee with satisfaction... but loo! Nothing at all has changed, everything's as lame as before, you still have only 2 minutes playtime. How disappointing: how comez it didn't work?

Well, for a start you have not been attentive enough! The search in debug gave you TWO locations, you moron, and not just the one you just tampered with. Check and you 'll see that the second location (cs:3EEA) is a MIRROR/CONTROL location (more on this later). Some times there exist "double" locations... coz at times it's quicker to use a double routine than to use a branching if or switch structure... some times the second locations do mirror the first ones and correct them on the fly if need be.

So you need to modify this too... you act as said above but this time you enter in debug a

-e cs:3EEA+4 EE

before writing back the dead file and then renaming it to exe and then running it... and loo! Hoow sloow! THERE YOU ARE! Your crippled POOLDEMO.EXE is now (sort of) unprotected: You think that you can now play the stupid game up to 12 minutes real time, even if the protection scheme (and the counter) "believes" that it is playing only two minutes.

So you begin to play, and the seconds look veeery sloow, and everything seems OK, but -alas- NO! At screen second 28 you get the irritating "two minutes are over" nag screen! Obviously you were dead wrong: the program "knows" the time directly from the timer... you only modified the stupid counter ON THE SCREEN.

So it's back to cracking, and now you are angry, and forget the quiet ways of the zen-analyze and begin the heavy cracking you should reserve -if ever- for really complicated schemes. You now start to check the hooked vectors (you did your routinely VECS_save before loading pooldemo in [Soft-ice] and your VECS_compare afterwards) and you see some findings that you believe interesting:

     vecs c 
     08   1EFD:84C6 0CD1:17AC <- the clock 
     09   1EFD:85EC 136A:069C <- the keyboard 
     22   0BCE:02B1 0BCE:017E <- the terminate

That's more like it -you think. Smack at the beginning: the first hooked vector does it! It's good old interrupt_08: the timer_clicker!

Some basics for those of you that do not know anything: INT_08 controls indirectly the INT_1C timer interrupt. The 8253 clock chip generates an IRQ_0 hardware interrupt at a rate of 18.2 interrupts per second. This gives control to the ISR (Interrupt Service Routine) that the INT_08 points to... and this should be at 0CD1:17AC, but has been hooked here, by pooldemo, to 1EFD:84C6.

One of the actions taken by the INT_08 ISR within the BIOS is to issue a software interrupt call to INT_1C, just in case any software modules within the system have established an intercept. If no intercepts have been established, the default contents of the INT_1C vector point to an iret instruction within the BIOS, so that a null action results.

Normally a protectionist would intercept INT_1C, coz at every ISR from INT_08 the CPU would fetch the contents of the corresponding interrupt vector and make an interrupt style call to the code at that address (which should contain the iret at address F000:9876 but can contain any trick they could think of).

So -you think- the protectionist hooked here INT_08 directly (a pretty infrequently used protection scheme by the way): What now?

A rather drastic measure would be, in such circumstances, to disable the IRQ_0 level timer interrupt, which is controlled by bit 0 of the mask register, at address I/O 0021h. When bit 0 within the mask register is set to 1, no further interrupts will be recognized for this IRQ level. This unfortunately won't work here, but it's an interesting technique per se, so you better learn it anyway, just in case you should need it elsewhere:

--- Trick to disable the timer ("IRQ_0 masking" by +ORC) --- 
*    prompt $t and hit ENTER a few times, see how the dos_clock 
     is merrily ticking along? 
*    enter DEBUG.COM 
*    Assemble using the command 'a' 
- a 
in al,21 
or al,1 
out 21,al 
ret 
RETURN 
RETURN    <- twice to exit immediate assembler 
- g 100   <- to run the tiny program. 
- q       <- to quit debug.

prompt $t is still on: hit ENTER a few times:
whoa! The clock has stopped advancing!

Compliments: you loaded the current mask register's contents into AL, you set the mask bit in the bit 0 position (which corresponds to IRQ_0) at then updated the value back to the mask register.

When you are ready to activate IRQ_0 events again, reenter DEBUG, run the following and then reset the clock you stopped with DOS TIME command:

- a 
in al,21 
and al,fe 
out 21,al 
ret 
RETURN twice 
- g 100 
- q

A word of caution: with the timer click disabled some processes will not operate correctly: once you access the diskette drive, the motor will continue to run indefinitely afterwards, etcetera.

Unfortunately the above technique cannot work with our [pooldemo.exe], where you now are looking closely to the INT_08 hook you found, believing that it hides the protection scheme: herein you find immediately the EoI (End_of_interrupt: MOV AL,20h... OUT 20h,AL). Both controllers have a second port address at 20h (or 0a0h), from which the instructions are given. The most important is the EoI command (20h). This instruction indicates the end of the interrupt handler and frees up the corresponding controller for the next interrupt. If somebody writes a new custom interrupt handler (as many protectionists do), it's up to him to see to it that at the end of the handler the EoI command (20h) is written to either port 20h or port 0a0h.

After the EoI follow the usual pushes, then some CALLS then a call that issues some OUT 40,AL that look like timer refreshing (OUT transfers data to an output port and ports 40-42 correspond to the Timer/counter). Some do_maintenance follows, then a double CALL, one more conditional CALL and then a "mysterious" call FAR CS:[AA91] on which depends a byte PTR[970C] that decides another final CALL... then the routine pops all registers and irets away.

Ah! You say, and begin disassembling, reverse engineering and looking inside each suspect call (the quicker method in these cases is to breakpoint calls on entrance and see if you find the one that's only called at the awakening of the time limit protection).

You work, and work, and work... and eventually find nothing at all, coz the protection of this program is NOT HERE!

Back to the zen-analyze of the snap printings... we forsake it too soon, as you will see.

If you watch with more attention the compare locations for the range DS:0 DS:FFFF you 'll notice that one of them changes relatively slowly from 0 to 1 to 2 to 3 and so on... the precedent location changes very quickly, and runs the complete cycle 0...FF. That's a counter, at locations DS:0009 and DS:000A! How long will it tick along? Well, we saw above that the "charge" every second is 3C, so it will be x3C*x78=x1C20, coz x78 is 120 seconds, i.e. the two minutes time limit.

Now search this 1C20 value around inside the code (protections are most of the time at the beginning of the CS:offset section), and you 'll find quickly what follows:

The protection in [pooldemo.exe] is at code_locations

CS:0A8A   813E20A7201C   CMP  WORD PTR [A720], 1C20 
                         compare location A720 with limit 1C20 
CS:0A90   7C07           JL   okay_play_a_little_more 
CS:0A92   E834FD         CALL beggar_off_time_is_up 

     BINGO!: FOUND!

Now let's quickly crack it:

------------------------------------------------ 
CRACKING POOLDEMO.EXE (by +ORC, January 1996) 

ren pooldemo.exe pooldemo.ded 
symdeb pooldemo.ded 
-    s cs:0 Lffff 81 3E 20 A7 20 1C 
xxxx:yyyy           <- this is the answer of the debugger 
-    e xxxx:yyyy+5 4C  <- this time limit is much better 
-    w 
-    q 
ren pooldemo.ded pooldemo.exe 
-------------------------------------------------

We have done here a "weak" crack: we limited ourselves to accept a (better) time limit, changing it from 1C20 to 4C20 (4 minutes instead of two). We could obviously have done a more radical crack if we had changed the JL (jump lower) instruction in a JMP (jump anyway) instruction. In this case it would have worked, but for reasons that will be explained in lesson 4, you should choose a rather delicate approach in cracking when you deal with time-limit protection schemes.

As you have seen, in this artificial cracking session we found the protection scheme after a little snooping around. But, as you will see in the hands on part, there are always MANY ways to crack a single protection scheme. You could -for instance- have found this protection the other way round: set a trace on memory range for the program, restricting the trace to the first part of it (say CS:0 to CS:1000, if you do not fetch anything you can always try the other blocks). Breakpoint at the nag screen, have a look at the last 300-400 backtraced instructions, if you did not move anything, everything will follow a repetitive pattern, until the protection snaps on:

       ... 
       JL 0A99 
       CMP BYTE PTR [A72A],01 
       ... 
       JL 0A99 
       CMP BYTE PTR [A72A],01 
       ... 
       for ages and ages and then... 
       ... 
       JL 0A99 
E834FD CALL 0759           <- BINGO! (CALL beggar_off_time_is_up)

... there it is, found the other way round. (But this apparently better method is unfortunately very unstable: it depends on your timing of the breaking in and on the distance between protection and nag screen, therefore the somehow more complicated, but more sure previous one should be favoured).

The reason why "minimal" approaches in cracking are often more successful than heavy vector_cracking, is that the programs are hardly ever "overprotected", and therefore the protections are seldom difficult to find (and those that are really worth cracking for study reasons).

Sometime you don't even need to crack anything at all! Some applications are fully functional -per se-, but have been crippled in a hurry in order to release them as demos. The commercial programmers want only money, do not even try to understand our zen ways, and do not care at all for a well done job. That means, among other things, that the hard disk of the user will be cluttered with files that the main program module never calls. A typical example of this sloppy method is the demo of [Panzer General] from SSI that appeared in the summer '95. This was in reality no less than the complete beta version of the game: you just had to substitute to one of the two "allowed" scenarios one of the 20 or more scenarios of the beta version in order to play them freely... you didn't ever need to crack!

The pooldemo crack example above should not discourage you from cracking intuitively. Be careful! Perform a thoroughly zen_analyze before attempting deeper methods: do remember that you want to crack the protection scheme SOMEHOW, and not necessarily following the same line of thought that the programmer eventually WANTED YOU TO CRACK IT with.

Well, that's it for this lesson, reader. Not all lessons of my tutorial are on the Web.

You 'll obtain the missing lessons IF AND ONLY IF you mail me back (via anon.penet.fi) with some tricks of the trade I may not know that YOU discovered. Mostly I'll actually know them already, but if they are really new you'll be given full credit, and even if they are not, should I judge that you "rediscovered" them with your work, or that you actually did good work on them, I'll send you the remaining lessons nevertheless. Your suggestions and critics on the whole crap I wrote are also welcomed.