Reverse Code Engineering RCE CD +sandman 2000/ReverseCodeEngineeringRceCdsandman2000.iso/RCE/+Sandman/Htocrk20.txt

Text File | 2000-05-25 | 30KB | 1,026 lines

                     HOW TO CRACK, by +ORC, A TUTORIAL

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                  Lesson 2: tools and tricks of the trade

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                                 [INDY.EXE]

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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 crack 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 lusers

to crack programs.

     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 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), system calls are probably 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

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 of the development.

     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 locate

the address of the message string and then survey the reminder

of the file for any instructions that reference this address.

[Sourcer] can generate labels for specific memory locations and

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

running the application you want to crack. 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 or "step"

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 (on segment zero).

21h + 21h = 42h                         42h + 42h = 84h

The int_21 vector is located at address 0000:0084

You could also use a calculator, for instance, the address of

INT_63 is 63h*4=18ch               ->   0000:018C



* 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

Before starting this section, for those of you that do not know

anything, here is the ARCHIE way you get all the program that do

EXIST on the planet: e-mail following

1) (address)   [e-mail]

I use this french archie, but you can get a worldwide list using

the metacommand "servers"

2) (text)      set search sub      <- anywhere in string

               set maxhits 140     <- (100-1000)

               set maxhitspm 15    <- not just 1 file all over

               find stepdos        <- search e.g. this file

Wait two hours, get your post and ftp the file you wanted (and

YES!, you 'll find also EVERYTHING else for free on the Web).

You could, instead of using archie, also learn how to use YAHOO.

[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 Horàk could easily be

the best one, and comes with source code(!). 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, by Mike Parker, 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 cracked (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 ARCHIE and YAHOO in order to find them. Your

debugger is the only tool you 'll REALLY need, believe me. So

choose your weapon wisely and learn how to use backtrace ranges

and (FOREMOST!) 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 (all the

programs that EXIST for that matter) 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 still wont be a cracker. In order to crack higher 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 this tutorial part 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 protection is based on the typing, at the nag

screen, of the correct sequence of numbers. Our example is a game

for the reasons explained in lesson 1, but you 'll find the SAME

protection scheme in the access protection procedure of some old

Tapestry networks... so do not frown upon games protections.

INDIANAPOLIS 500, Papyrus software & Electronic Arts, 1989

It's a rather widespread program, you should therefore 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 (described in

-> lesson 3.1) 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 crack it's relatively quick and should be most of

the time fairly effective, but there is a better way: the "zen

way", the only one that can really enable you to crack high

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  beggar_off_coz_false_answer

  0AC0    OR   AL,AL     <-- more numbers?

  75F2    JNZ  compare_loop

  59      POP  CX        <-- all OK, go on, nice guy

  ...

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.

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CRACKING INDY.EXE (by +ORC, January 1996)

ren indy.exe indy.ded

symdeb indy.ded

-    s (cs+0000):0 Lffff B4 FF 2A 25 47 3A C4 75 1A

xxxx:yyyy           <-- this is the answer of the debugger

-    s (cs+1000):0 Lffff B4 FF 2A 25 47 3A C4 75 1A

(nothing, but you must be sure there isn't a mirror)

-    e xxxx:yyyy+8 00    <-- "JNZ 1A ahead" changes to "JNZ 0"

-    w

-    q

ren indy.ded indy.exe

-------------------------------------------------

Cracked: you just changed the JNZ beggar_off instruction in a JNZ

go_ahead_anyway. Nice, isnt'it?

WHY WE CRACK

     Strange as it may seem, the reasons for cracking are very

important for the success of our task. We (at least we old

crackers) crack AGAINST society, and OPPOSING laws and

conventions. We usually DO NOT crack for money or for other

"commercial" reasons (just sometimes, and we are expensive: I

have plenty of money already and my services are VERY expensive

if you need an aimed deprotection). But in general we don't care

much for money and -as you can see- I am giving away the basis

of what I know for free with this tutorial. The programs we crack

should be made free for everybody, even if we spent some of our

time deprotecting them. We could not care less of the commercial

value of a given program, not to mention the holy work of the

ethical programmers... we program ourselves, but only because we

LIKE it... if somebody does something only in order to gain

money, he does not deserve anything. It's the mind challenge that

counts, NEVER the profit! (Even if you can make good use of the

cracked programs and even if -as I said- there is at times a

personal profit).

     This is an indispensable attitude! Only a non-mercantile

mind can leap forward to the "satori" knowledge that you

desperately need if you want to crack quickly and elegantly huge

iperbloated monstruosities that somebody else wrote and

protected, or if you want to gain access to some hidden

information, data that you would like to snoop but that somebody

declared "off limits", coz a stupid government, or useless

industry sector, or money oriented programmer or dirty lobby of

interest decided it.

     If you do accept the society where we are compelled to live,

its awfully egoistic way of life and its dirty "profit" values,

you may eventually learn how to disable some simple protections,

but you'll never be able to crack in the "right" way. You must

learn to despise money, governments, televisions, trends,

opinion-makers, public opinion, newspapers and all this

preposterous, asinine shit if you want to grasp the noble art,

coz in order to be emphatic with the code you must be free from

all trivial and petty conventions, strange as it may sound. So

you better take a good look around you... you'll find plenty of

reasons to hate society and act against it, plenty of sparks to

crackle programs in the right way... Hope all this did not sound

too cretin.

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.

                                E-mail +ORC

                        +ORC [e-mail]