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HOW TO CRACK, A TUTORIAL - LESSON 2 by +ORC (the old red cracker) How to crack, an approach LESSON 1 -> How to crack, tools and tricks of the trade LESSON 2 How to crack, hands on, paper protections LESSON 3 (1-2) How to crack, hands on, time limits LESSON 4 How to crack, hands on, disk-CDrom access LESSON 5 How to crack, funny tricks LESSON 6 (1-2) How to crack, intuition and luck LESSON 7 How to crack windows, an approach LESSON 8 How to crack windows, tools of the trade LESSON 9 How to crack, advanced cracking LESSON A (1-2) How to crack, zen-cracking LESSON B How to crack, cracking as an art LESSON C How to crack INDEX LESSON 2- How to crack, tools and tricks of the trade LOST IN THE DARK CODEWOODS When you break into a program you end up in portions of code that are unfamiliar to you. It is also not uncommon for the breakpoints to occur outside of the confines of the program you want to crack. Getting your bearings is, in these cases, very important. One of the handiest utilities is the memory dump tool -it tells you where all the device drivers and TSR are loaded, in which memory locations the program you are cracking dwells, how much memory is left and what the next program load point is. The tools you use should report on the following: - the contents of interrupt vectors - the state of the BIOS data area, beginning at address 40:0 - internal structures within DOS, such as the MCB chain, the SFT (System File Table) chain, the chain of installed device drivers, the PSPs and memory allocations associated with installed TSRs - memory allocation statistic from XMS and EMS drivers When seeking to understand a section of foreign code, you must be especially careful to seek the real intent of the code. Consider using a profiler prior to undertaking an analysis of an unfamiliar program. This will help you by ensuring that you don't waste time studying sections of the program that aren't even involved in the protection scheme you are chasing down. Using a utility that charts a program's calling hierarchy can give you an important perspective on how your babe conducts its internal operations. YOUR DEBUGGER: YOUR FAVOURITE TOOL First and foremost, your debugger must be designed for use with resident modules (or must be itself a resident module). Trying to crack with simplistic [debug.com] is a sure way to get absolutely nowhere. We recommend Softice.exe from Nu-Mega technologies (Version 2.6 [S-Ice.exe] has been cracked by MARQUIS DE SOIREE and its vastly available on the Web). You could also use [Periscope] or [Codeview] or Borland's Turbodebugger... all these programs have been boldly cracked and/or distributed and are now on the Web for free... learn how to use YAHOO and find them. In emergency cases you could fix some quick cracking patches using [debug] or [symdeb], but, as said above, most of the time these older debuggers won't do. I'll nevertheless ALWAYS give the final crack procedure for [debug.com], in order to permit even idiots to crack their programs (altruistic, isn't it... besides, every wizard has started with debug.com). When you first smell a protection, it can be tempting to immediately begin your crack using invasive types of techniques. While there is certainly nothing wrong with this approach, provided that you are fairly familiar with the protection scheme used, going in too deep too soon can be a problem when you don't have a strong hunch. Most of the time you'll end up missing important details. So first of all sit down and ponder... that's the zen-way, the only one that really works. Single-stepping is expensive, not only because of the time it requires but also because of the amount of detail with which you must contend. Your immediate goal is to home in on the protection scheme through a series of successively refined traps, your broader aim is to get an overview idea of the program's action... the wise use of breakpoints will condense these minutiae into an understandable form. The first step is to try to identify the section of the program where the protection scheme is snapping. Once you are able to isolate a certain section of a program, breakpoints can be used to gather a trace history of the program's execution. If your debugger sports a backtrace buffer, logging window, or similar feature, by all means learn how to use it. The debugger it's your best weapon, you must know all the possibilities it offers and all the capabilities it possesses. Having a debugger's display output echoed to a printer is another possibility. Using breakpoints is beneficial for two basic reasons: speed and reduction of detail. Manual single-stepping is invaluable when you are close to the protection scheme, but too much of it will bore you to death. When selecting breakpoint locations and the types of breakpoint to use, it is important to step back once more, drink a cool Martini-Wodka (use only Moskovskaja: non-russian Wodkas are appalling) and ask yourself: "What is this going to tell me?" and "What else will I need to know once the break occurs?". MOST IMPORTANT OF ALL: "Is my current cracking approach the simplest and most direct?", coz you do not want to waste precious cracking time. When devising a set of breakpoints it is wise to consider how "a trail of bread crumbs" can be left. Not allowing for an execution chronicle from the start can mean having to restart a cracking session. Setting breakpoints on certain software interrupt calls is an excellent way to get an overview of a program's operations. The INT_21 DOS services interrupt is probably the most universal useful of these, with BIOS interrupts such as the INT_13 (BIOS Disk services) and INT_16 (BIOS keyboard services) useful for specific cracking. When working with a debugger, evaluative breakpoints are usually your best shot. To avoid having to deal with a plethora of calls, you would want to have a debugger capable of being told to "break on any INT_21 call except where AH == 2C or AH == 0B". A real understanding of the working of a program is surely important, but don't overdo it! To reverse-engineer even a small program can involve many hours of analysis and documentation work. If you'll not be able to use the zen-cracking techniques described in this tutorial (sadly not everybody can) pace yourself and make sure your chair is comfortable: you'll be sitting for quite a spell. Much of the work involved in reverse-engineering consist of chasing down tentacles. In order to understand the operations of one function, you must understand what happens within each of the functions it calls- its child functions. To understand these child functions you must study their children; and so on down the calling hierarchy tree. Then there is the data. Tracing tentacles based on a program's calling hierarchy is a directed process. Each function you encounter is basically a list of other functions you must reckon with. When it comes to analyzing a function's interrelationship with the program's data structure, no such list is provided. You must have instinct, feeling and luck. Data analysis requires more of a broad-based inquisition. For each memory variable you are interested in, you must survey all functions to determine which ones read and write that variable. The use of memory conditional breakpoints and of a disassembler that builds a cross-reference table can make this task a lot easier. (Use Sourcer! It's a fairly good tool and version 4.08 of [sr.exe] has been long ago cracked by me, +ORC, and distributed on the Web). ALL SYSTEM CALLS IN ONE LOCATION Remember that if the program you are cracking was written in assembler in the first place (very unlikely knowing the laziness of to_days programmers), it is probable that system calls are made directly from the functions which need them. But when a program is developed in a high-level language, it is more likely that common library functions will be used for many operations involving system calls. When a program makes all of its INT_21 calls from the same location, you know that this is certainly the case. Now, what happens sometimes is that the programmers write the whole application in a overbloated language like C++, but are afterwards compelled to "speed up" critical sections of the code writing them in assembler. And loo! A section where you repeatedly find assembler crafted patches is precisely the section containing the protection scheme! So you could have a program with all INT_21 calls from the same location but for one or two calls which are coming out of the section where the morons have "hidden" their protection strategy. By just "looking" at the dead code of a program, you should be capable to tell wich parts have been "added on" in a later phase. They presents themselves as unevenness and irregularities, especially if you use an utility that represents graphicallly the code of a program. Protections are often added on at the end. Should you determine that the system calls relevant to your cracking are made from common library functions, all is not lost. The specific function from which these library calls were made, the function you are seeking to locate, is executing at some point in between these calls. Break in with your debugger at the end of the first system call, just where it is returning to the point of call. From there, trace through the remainder of the common library routine until it returns to its caller. In short order, you should find yourself in the function you need to see. The trick is to be able to identify it for what it is. ASCIIZ IN CODE In the interest of gaining an overall familiarity with the program you want to crack, it can be enlightening to use a hex dump utility to examine the message strings contained within the program's binary modules. If the program happens to load its message strings from separate files, your search has just been simplified. Your debugger's memory-dumping feature is one tool that can be useful for this type of exploration. You could also construct a filtering program, which would read a binary file and output all sequences of bytes that are comprised of displayable characters and are over a certain minimum length (the best cracker tools are often the ones you write yourself). When a protection scheme is marked by the issuance of a specific message on the screen, you could go into the program and locate the code that emits this message, and then determine what triggers it. A good way to start the location process is to see if a system call is used to display the string. Interrupt INT_21, INT_10 or INT_29 are usually used to display text messages to the console. When the message's display is not a result of one of these system calls, direct video writing is probably being used. If you know the screen location used, and if that part of video memory is not used for anything else at the time (a big if), a memory write breakpoint could be set on the video buffer address corresponding to the first character's position. If this won't work, use the step-over/step-around tracing technique while watching for the message to appear. Now you found it: from a disassembled listing, you could locate the address of the message string and then survey the reminder of the file for any instructions that reference this address. [Sourcer.exe] can generate labels for specific memory locations and then generate a cross-reference table showing where these labelled locations are referenced. Otherwise, load the disassembled listing file into your editor and use its search capabilities. Manually searching for such things in a listing will make you old before your time. CODE AND DATA When stepping through code at the assembler level, watch out for interrupt calls that are followed by data. Sometimes you will find an interrupt call, typically within the range INT_34 to INT_3F, where several bytes immediately following the interrupt instruction will be data rather than code. Be especially suspicious of this type of code-and-data mixture when your debugger's disassembly output of the instructions immediately following an interrupt call doesn't make sense. Sometimes you can determine the offset of the next true instruction by inspecting the following code and data. In other cases, you will have to trace through the interrupt call to see how it accesses the data following the interrupt call instruction and how it manipulates the return address on the stack. HOOKED VECTORS Seeing what interrupt intercepts already exist within a system before running the program you want to crack, as well as what interrupt handlers are established by the target program, can provide useful clues. For example, if a protection establishes an INT_09 intercept just before the snapping of a keyboard verification routine, your range of suspects has just been narrowed significantly. To study the interrupt vector activities of an application, a vector dump map utility is useless. It can't be run while the application you want to crack is running. One solution is to run the program under a debugger and watch for system calls to INT_21 functions 25h (set interrupt vector) and 35h (get interrupt vector), but in the event that the program reads and writes interrupt vectors directly, this method will not give you a complete picture. Normally you'll use a spy (trace) utility. APPLYING A MEMORY WRITE BREAKPOINT TO A SPECIFIC VECTOR OR TO THE ENTIRE TABLE is another way to deal with this. Note that some sort of direct vector writing must be occurring if a vector change is detected between system calls. If a vector change is detected during a system call but it isn't function 25h of INT_21, suspect that an IRQ handler may be effecting the change. LITTLE TRICKS OF THE TRADE: determining interrupt vector addresses How do you determine the interrupt vector addresses? As example let's find the address of the INT_21 interrupt vector. Since the interrupt vector table starts at address 0000:0000 (easy to remember, isn't it?) and there are four bytes per vector, the basic process is to multiply the interrupt number four times and use the result at the offset with a segment of zero. x21h + x21h = x42 x42h + x42h = x84 The int_21 vector is located at address 0000:0084 You could also use a calculator, for instance, the address of INT_63 is x63*4=x18c = 0000:018C LITTLE TRICKS OF THE TRADE: address conversion After a painstaking cracking session, you have finally determined that a byte of memory at address 6049:891C is the trigger. But when you isolate the offending instruction, you find that the address it is generating when the protection occur is different, being 6109:7D1C instead! How can this be? An 80x86 type CPU, when running in real or VM86 mode, uses what is known as segment:offset type addressing. One side effect of this addressing method is that one physical address can be equivalent to many different segment:offset addresses. To find the PHYSICAL ADDRESS for a given segment:offset do the following: - convert the segment portion of the address to a 1-based number by multiplying it by 16 (x10)... it's easy: add 0 at the right end of the number!... 6049 -> 60490 6109 -> 61090 now all you have to do is to add this value to the offset value 60490+891C -> 68DAC 61090+7D1C -> 68DAC Got it? And the other way round? If you have a physical address, say 19AC3, and you want to obtain a segment:offset address you must first of all decide in which segment you want the address... if, say, you choose segment 16CC, you proceed as follows: 16CC -> 16CC0 19AC3-16CC0 = 2E03 (offset) address for 19AC3 in segment 16CC = 16CC:2E03 TOOLS OF THE TRADE [MEMSCAN.EXE] One of the most fascinating tools that I have ever seen is a (very old) program: MEMSCAN.EXE. This program was originally written in 1988 by Scott A. Mebust, running in CGA. It's a "visual" utility: it enables you to see graphically the 1-meg of PC memory in 8 kbyte chunks. It's a powerful tool in order to locate quickly bit mapped graphics and other 'objects' in memory, like program data tables, stack areas, code areas, available RAM, etc. I used this great idea to create (in C) my own tools: a "dead_programs scanner" and an ameliorate version of Memscan itself. Looking at the VISUAL STRUCTURE of a program it's a great help when you'll crack higher levels. [TRACKMEM.COM] A very good tool by James W.Birdsall, tracks memory usage of programs (EMS, XMS, conventional). [SCANCODE.COM] "THE" scancode lister, by the code_masters from clockwork software. The must utility for crackers that do not learn all scancodes by heart. [MAP.EXE] Actually "MAP2", THE memory mapper from the code_masters at clockwork software. It's a very good tool and an interesting one too, coz you get it with the "Nigel" nag screens. They are not difficult to remove (a "passletter" protection scheme, you'll learn how to find and remove it from [Map.exe] in LESSON 3.2). [FILEDUMP.COM] [HEXDUMP.COM] [TDUMP.EXE] [DUMP.EXE] There are hundred of file dump utilities, coz file dumping is one of the first exercise they learn you at C-school. Hexdump.com is 558 bytes long, Tdump.exe 120.704, pick the one you like better or write your own (even better). Filedump.com, by Daniel M.O'Brien, 1046 bytes long, it's nice. [SPRAY.COM] That's a good crack utility indeed! This 1989 program by Daniel M.O'Brien gives you a "post-mortem" picture of your memory. You redirect it to <myfile> and study it at ease. It's difficult to say how many hours of cracking it did spare me (you should study the program, only 252 bytes long, and will have to modify it a bit, coz it's pretty primitive, in the original version, for instance, the redirection to the printer works only if there is NO SPACE between "spray" and ">"). [VEXE.EXE] A good EXE files analyzer, useful for windows programs too (see --> LESSON 7). Some of its functions are present in TDUMP.EXE too. This 1991 program by S.Krupa it's sometimes very useful. [SNOOP UTILITIES --> KGB.EXE INTMON.EXE INTRSPY.EXE etc...] [TRACE UTILITIES --> TRACE.EXE STEPDOS.EXE etc...] A must to study the "calling hierarchy" of an unknown program. KGB.EXE, a 1992 program by Petr Hor k could be the best one. I'll teach you how to crack without any of them (you do not need them if you zen-crack), but they can nevertheless be very useful in some situations. Stepdos.exe is a excellent program: a pleasure to crack in order to use it for slightly different purposes :=) [SOURCERING UTILITIES] SR.EXE can be used for sourcering unknown programs. It's a fairly good sourcering tool. Version 4.08 has been long ago cracked by me (it's a "ORIGINAL NUMBERCODE" protected program) and distributed on the Web, so you should easily find it. This said, you should NEVER use such a brute force approach, unless you are really desperate: I'll teach you how to crack without sourcering (you don't need to sourcer if you zen-crack). [HEXEDITORS] Every idiot has written at least one hexeditor, and you can find very bad tools everywhere (the SIMTEL collection, on the Web, lists at least 35 hexeditors). I suggest you write your own and contribute to the flood, or (better) get PSEDIT.EXE, a good 1990 program by Gary C. Crider (Parity Solutions, 1903 Pavia Ct. Arlington, TX 76006... sometimes even americans can write good programs). If you do use it (as you should) disapt the nag screen as small exercise in cracking. [DEBUGGER] Your best friend in cracking, your weapon, your hidecloak... I suggest [Softice.exe] from Nu-Mega technologies (Version 2.6 has been cracked by MARQUIS DE SOIREE and its vastly available on the Web). You could also use [Periscope] or [Codeview] or Borland's Turbodebugger... all these programs have been boldly cracked and/or distributed and are now on the Web for free... learn how to use YAHOO and find them. It's the only tool you 'll REALLY need, believe me. So choose wisely and learn how to use backtrace ranges and breakpoint on user written qualifications routines. You 'll be able to crack almost EVERYTHING using these features in the right way. You should get all the programs mentioned above (and more) for free on the Web. Use them, but also modify them recklessly! REMEMBER THAT YOU ARE (GOING TO BE) A CRACKER! The first programs you should crack and modify are therefore your very tools! So steal the code of the best tools you find! Snatch the best routines and change them for the better! That's the whole point in cracking: a mission to IMPROVE the best accomplishments of humanity's genius :). HOW TO CRACK, ZEN-CRACKING You 'll learn, beginning with next lesson, how to crack systematically the different protection schemes: paper & password protections, time protections, access protections. At the end of the "methodolocical" part, you'll be able to deprotect programs, but you will still not be a cracker. In order to crack in a real effective way you must use what I call (lacking a better definition) "zen-cracking". I 'll give you right now an example of this, so that you know what I'm talking about, but -unless you are already capable- you'll have to finish the tutorial for "normal" cracking before attempting this techniques. Let's zen- crack together a password protection scheme (aka "paper protection", coz you need the original manual of the program in order to answer). This one is based on the typing, at the nag screen, of the correct sequence of numbers. We are using as example a game for the reasons explained in lesson 1, but you 'll find the SAME protection scheme in the access protection procedure of the old Tapestry networks... so do not frown upon games protections. INDIANAPOLIS 500, Papyrus software & Electronic Arts, 1989 It's a rather widespread program, so you should be able to find it pretty easily. The nag screen asks for data based on the historical performances of race cars... that means that the answers will consist in two to three digits. Now, the normal way to crack such a program will be described in lesson 3.1 and embodyes following steps: - snap save program memory areas before typing your answer - snap compare after typing, say, "666" - search for the sequence 36,36,36 (i.e. 666) - breakpoint on memory range for reading - look at the program part fetching your data - find the snap procedure - disable it. The above it's a relatively quick crack, and most of the time 'll be fairly effective, but there is a better way: the "zen way", the only one that can really bring you to crack peculiar protection schemes. - Run the program and break in at the nag screen - Answer consist of 2-3 digits? Search for "AC" (i.e. the instruction LODSB, load digit of answer in AL) in the area 500 bytes BEFORE and 500 bytes AFTER your position. You'll get some locations. (In the case of INDY 500 you get 6 such locations). - "feel" the locations (that's the tricky part). - OK, you already made it! Here is the protection strategy: 8BBF28A5 MOV DI,[BX+A528]<-- DI points to coded data area :compare_loop AC LODSB <-- load first digit of answer in AL B4FF MOV AH,FF <-- load mask in AH 2A25 SUB AH,[DI] <-- sub coded data from mask and get real answer 47 INC DI <-- ready to get next coded data 3AC4 CMP AL,AH <-- user answer = real answer ? 751A JNZ bagger_off_you_do_not_know_the_right_answer 0AC0 OR AL,AL <-- more numbers? 75F2 JNZ compare_loop 59 POP CX <-- nice guy, you may go on ... And if the protection scheme had been more far away? And if you cannot "feel" the right one? And if my grandma had wheels? You'll learn it, believe me. Now let's quickly crack this crap.