The Cracking Manual ������������������������������������������������������������� Written By The Cyborg - April 3, 1992 Disclaimer The author of this text shall hold no liability for special, incidental, or consequential damages arising out of or resulting from the use/misuse of the information in this file. The Cracking Manual INTRODUCTION Introduction ------------ Welcome to the wonderful world of cracking. What is cracking? If you don't know and you're reading this, ask yourself why? Anyway, cracking is the art of removing copy protected coding from programs. Why do this? In recent years, software companies have been fighting to keep copy protection in their software to avoid their work to be illegally copied. Users feel that such copy protection is ridiculous in that it violate their own rights to make backups of their sometimes expensive investments. Whichever side you may favor, this manual will go into some detail on removing copy protection from programs. If you feel offended by this, then I would suggest you stop here. Please note, I do not endorse cracking for the illegal copying of software. Please take into consideration the hard work and effort of many programmers to make the software. Illegal copying would only increase prices on software for all people. Use this manual with discretion as I place into your trust and judgement with the following knowledge. Page 1 The Cracking Manual WHAT YOU WILL NEED What You Will Need ------------------ Like all programming, cracking is the debugging stage of software development. It is the most tedious and hectic part of programming as you shall see. However, unlike software development, you are given no source code, only the machine level code commonly called machine language. Cracking demands patience. No patience, no cracking. Before we begin, you will need certain tools. These include: - A decent computer. By this, I mean at minimum a 286 computer with 2 or more megs of RAM. A 386 is the ideal since it can load a debugger into usable memory. - A source level debugger (eg. Turbo Debugger) - A low level debugger (eg. DEBUG) - An assembler system (eg. MASM, LINK, EXE2BIN) - A hex dumping program (eg. Norton Utilities) The source level debugger is what you will try to be using most of the time. It provides many features that are a convenience to the cracker, such as interrupt redirection. Become comfortable with its features. However, in some instances, the source level debugger may not be suitable for cracking huge games since the debugger itself may take up too much memory. In such a case, a low level debugger must be used since their memory usage may be considered negligible. This manual will focus on its use. The assembler package will be used in the creation of the famed loaders, which provide the cracker with dynamic memory alterations without changing the original program. Page 2 The Cracking Manual CRASH COURSE IN ASSEMBLY LANGUAGE Crash Course in Assembly Language --------------------------------- If you are already well familiar with the assembly language, you may wish to skip this section. Cracking demands the knowledge of assembly language. If you wish to become a "serious" cracker, you might like to read up more about this fascinating language. This section will only give you enough info for intermediate level cracking. At this point, you should familiarize yourself with DEBUG and its commands as we will be using them shortly. Registers --------- One of the neato things that you will be fooling around most often with are called the registers. Registers are like variables (such as in BASIC) that are located within the CPU itself. These registers may hold a positive integer from 0 to 255 or from 0 to 65535. They can also hold negative integers from -128 to 127 or from -32768 to 32767. The registers are given names as follows: AX => accumulator - this register is most commonly used for mathematical or I/O operations BX => base - this register is used commonly as a base or a pointer register (we'll talk more about this later) CX => count - used commonly for counting instructions such as loops DX => displacement - much like the base register The registers stated above are considered general purpose registers, since they can basically be used to store whatever the user wants. Let's try putting some number in these registers. Type in "R {enter}". You should see a bunch of info, of which are four of the above mentioned registers. Now, type in "RAX {enter}". Then type in a number like 8FABh. Type in "R" again and noticed how the accumulator (AX) has change its number. These general purpose registers can also be "split" in half into its higher and lower order components. Instead of having one register AX, you can have two registers, AH and AL. Note however that while you have a range of 0 to FFFFh for AX, you will now have a range of 0 to FF for AH and AL. You cannot change these directly in debug, but be aware that programs will use it. If AX contains 0A4Ch, then AH will contain 0Ah and AL will contain 4Ch. The following are called the segment registers: CS => code segment - the block of memory where the code (instructions are located) DS => data segment - the block of memory where data can be accessed. In block move operations in which Page 3 The Cracking Manual huge blocks of memory are moved, this is commonly the segment in which the CPU reads from. ES => extra segment - also another data segment. In block move operations in which huge blocks of memory are moved, this is commonly the segment in which the CPU writes to. SS => stack segment - this is the block of memory in which the CPU uses to store return addresses from subroutines. (more on this later) In introductory level of cracking, we don't mess around with these registers. Later, we will see how we can use these to trick a program into thinking other things, but that's later. You can also change these registers in debug. Type in "RCS {enter}". Then enter "0 {enter}" and notice how the CS register changed. There are other registers that we use to see what the program is doing. These registers can also be change in debug. Included are the following: SI => source index - this register is used in conjunction with block move instructions. This is a pointer within a segment (usually DS) that is read from by the CPU. DI => destination index - this register is also used in conjunction with block move instructions. This is a pointer within a segment (usually ES) that is written to by the CPU. BP => base pointer - a pointer used commonly with the stack segment SP => stack pointer - another pointer used commonly with the stack segment (this one, you don't touch) By now, you may probably be confused about this segment/pointer bit. Here is an analogy that my straighten things out. Pretend you are in kindergarden learning to read. There are four black boards surrounding the room. These black boards are like SEGMENTS. Let's pretend the front blackboard is the code segment (CS). The teacher has written some instructions on pronunciation rules. This is what the students refer to when they try to pronounce words. In a program, this is what the CPU refers to when it follows directions. Okay, now the teacher has gone to the blackboard on the left of the classroom. We will call this board the data segment (DS). The teacher has also written a set of words on the board. Then she uses a wooden stick or a POINTER to point to a word. Let's pretend this stick is the source ...
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