Software cracking and patching
- 2. Introduction to Software Technology Introduction to Software Technology Introduction to Software Technology Introduction to Software Technology • Software is a set of instructions that determines what a general- purpose computer will do. Thus, in some sense, a software program is an instantiation of a particular machine (made up of the computer and its instructions). • Machines like this obviously have explicit rules and well-defined behavior. Although we can watch this behavior unfold as we run a program on a machine, looking at the code and coming to an understanding of the inner workings of a program sometimes takes more effort.
- 3. Reverse Engineering Reverse Engineering Reverse Engineering Reverse Engineering • Reverse engineering is the process of creating a blueprint of a machine to discern its rules by looking only at the machine and its behavior. At a high level, this process involves taking something that you may not completely understand technically when you start, and coming to understand completely its function, its internals, and its construction. function, its internals, and its construction. • A good reverse engineer attempts to understand the details of software, which by necessity involves understanding how the overall computing machinery that the software runs on functions. A reverse engineer requires a deep understanding of both the hardware and the software, and how it all works together.
- 5. Reverse Engineering (Cont.) Reverse Engineering (Cont.) Reverse Engineering (Cont.) Reverse Engineering (Cont.) • Think about how external input is handled by a software program. External "user" input can contain commands and data. Each code path in the target involves a number of control decisions that are made based on input. Sometimes a code path will be wide and will allow any number of messages to pass through successfully. through successfully. • Other times a code path will be narrow, closing things down or even halting if the input isn't formatted exactly the right way. This series of twists and turns can be mapped if you have the right tools.
- 7. Reverse Engineering (cont.) Reverse Engineering (cont.) Reverse Engineering (cont.) Reverse Engineering (cont.) • Generally speaking, the deeper you go as you wander into a program, the longer the code path between the input where you "start" and the place where you end up. Getting to a particular location in this house of logic requires following paths to various rooms (hopefully where the valuables are). • Each internal door you pass through imposes rules on the kinds of messages that may pass. Wandering from room to room thus involves negotiating multiple sets of rules regarding the input that will be accepted. This makes crafting an input stream that can pass through lots of doors (both external and internal) a real challenge. In general, attack input becomes progressively more refined and specific as it digs deeper into a target program.
- 9. Why Reverse Engineering? Why Reverse Engineering? Why Reverse Engineering? Why Reverse Engineering? • Reverse Engineering allows you to learn about a program's structure and its logic. Reverse Engineering thus leads to critical insights regarding how a program functions. This kind of insight is extremely useful when you exploit software. There are obvious advantages to be had from reverse engineering. • For example, you can learn the kind of system functions a target program is using. You can learn the files the target program accesses. You can learn the protocols the target software uses and how it communicates with other parts of the target network.
- 11. Why Reverse Engineering (cont.) Why Reverse Engineering (cont.) Why Reverse Engineering (cont.) Why Reverse Engineering (cont.) • The most powerful advantage to reversing is that you can change a program's structure and thus directly affect its logical flow. Technically this activity is called patching, because it involves placing new code patches (in a seamless manner) over the original code, much like a patch stitched on a blanket. Like any skill, reverse engineering can be used for good and for bad ends. • Patching allows you to add commands or change the way particular function calls work. This enables you to add secret features, remove or disable functions, and fix security bugs without source code. A common use of patching in the computer underground involves removing copy protection mechanisms. Note: Like any skill, Reverse Engineering can be used for Good and for Bad Ends
- 12. Debugger Debugger Debugger Debugger • A Debugger is a software program that attaches to and controls other software programs. A debugger allows single stepping of code, debug tracing, setting breakpoints, and viewing variables and memory state in the target program as it executes in a stepwise fashion. • Debuggers are invaluable in determining logical program flow. • Olly Debugger, Soft Ice, IDA Pro are some of the very famous Software Debuggers
- 14. Disassembler Disassembler Disassembler Disassembler • A Disassembler is a tool that converts machine-readable code into assembly language. Assembly language is a human-readable form of machine code (well, more human readable than a string of bits anyway). Disassemblers reveal which machine instructions are being used in the code. • Machine code is usually specific to a given hardware architecture (such as the PowerPC chip or Intel Pentium chip). Thus, Disassemblers are written expressly for the target hardware architecture.
- 16. Methods of Reverse Engineering Methods of Reverse Engineering Methods of Reverse Engineering Methods of Reverse Engineering • There are several methods that can be used while reverse engineering software. Each has benefits and each has resource and time requirements. A typical approach uses a mixture of methods when decompiling and examining software. The best method mix depends entirely on your goals. For example, you may first want to run a quick scan of the code for obvious may first want to run a quick scan of the code for obvious vulnerabilities. • Next, you may want to perform a detailed input trace on the user-supplied data. You may not have time to trace each and every path, so you may use complex breakpoints and other tools to speed up the process. What follows is a brief description of several basic methods.
- 18. Error Tracing Error Tracing Error Tracing Error Tracing • Error tracing is the most thorough of all Software Cracking methods. • First you identify the Text Strings in the software code and then look for the error message displayed to the user when a wrong look for the error message displayed to the user when a wrong serial number is provided to the software product. • Identify the working and flow of Program or Function