Registration number protections require the user to enter a registration number to register a software application. However, in most cases such a protection can be defeated easily by an in-depth analysis of the disassembled code or by tracing the applications execution using dynamic disassembly (debugging) techniques. Even there still is heavy use of simple XOR encryption methods, several software applications use high optimized cryptographic algorithms to prove the given input for validity. However, there are several approaches to deal even with such complicated calculations. Once the attacker identifies the algorithm routines, one approach is to use self-keygenning techniques, which produces always a correct serial number by turning the application against itself, which had been described by Webbit in detail [1]. Another approach is the common used code-ripping method, where the attacker extracts the relevant code segment and uses the extracted code to build up a keygenning application. Using self-keygenning or code-ripping, the attacker does not necessarily need to know exactly, how the algorithm works. The attacker just needs to be aware of initial settings, as register values.