Chapter 6. Deciphering File Formats
Most of this book describes how to reverse engineer programs in order to get an insight into their internal workings. This chapter discusses a slightly different aspect of this craft: the general process of deciphering program data. This data can be an undocumented file format, a network protocol, and so on. The process of deciphering such data to the point where it is possible to actually use it for the creation of programs that can accept and produce compatible data is another branch of reverse engineering that is often referred to as data reverse engineering. This chapter demonstrates data reverse-engineering techniques and shows what can be done with them.
The most common reason for performing any kind of data reverse engineering is to achieve interoperability with a third party's software product. There are countless commercial products out there that use proprietary, undocumented data formats. These can be undocumented file formats or networking protocols that cannot be accessed by any program other than those written by the original owner of the format—no one else knows the details of the proprietary format. This is a major inconvenience to end users because they cannot easily share their files with people that use a competing program—only the products developed by the owner of the file format can access the proprietary file format.
This is where data reverse engineering comes into play. Using data reverse engineering techniques it is possible ...