What does one need to reverse engineer? What does one need to crack? I should begin by pointing out that cracking and re-engineering are for the most part one and the same; cracking is a dynamic form of re-engineering--more like a surgical strike than a full de-compilation--that exploits flaws inherent in the program (or, more commonly, in the API of the OS) to achieve a certain end, while reverse engineering is the attempt to recover the original source code from an existing binary file--usually to copy or change the functions in that binary file. The skills and tools used for cracking and re-engineering are the same; re-engineering is just a more involved process.

First off, to re-engineer one must know assembly language. It is only necessary to be able to read ASM, not to program in it--though that skill will prove useful as well. In addition, one must be familiar with the language in which the target file was written--if it was written in Java, learn Java; if in C++, learn C++; if in Visual Basic, then you must lower yourself to learn that (for lack of a better word) language as well (and it may be worth learning, for more and more applications are being written in the psuedocode that is VB5 now that MS has become dominant in the PC market). You must have an intimate knowledge of your PC, especially the CPU and the memory addressing scheme. And finally, you must have patience and a good problem-solving ability.

The "tools" end of the package is much easier to fill. It is essential to have a disassembler such as W32DASM, WCB, or Sourcer; it is also good to have a debugger in order to clarify and correct the code produced by your disassembler. Numega's unbelievable Soft-Ice is the prime choice, but with a good disassembler one can get by with CodeView, Turbo Debugger, Brand-X or even DEBUG. An API reference for the language and OS of the target program is absolutely required, as well as a text editor or word processor (hopefully one that colorizes source code for a number of languages, such as Multi-Edit) that can handle the large files created by the disassembler (5 to 10 times the size of the original binary).

Any additional tools are more or less mandated by style--resource editors for Windows programs, hex editors to patch files, compilers for re-generating executables, and system monitor utilities for information gathering.

Oh yes, you will also need a computer. And lots of time to play with it....