It then chooses the T (true) or F (false) branch and updates the formula with this new constraint (or its negation). When a branch of the program is found during the execution, the engine transforms the condition into arithmetic operations. Dynamic Symbolic Execution (DSE) builds the logical formula at runtime, step-by-step, following one path at a time. If those values are used in the program, the execution reaches that program point. By solving a formula for one path, we get concrete values for the variables. Each instruction cause that formula to be updated. Symbolic execution translates the program's semantics into a logical formula. A symbolic variable is used whenever a value can be controlled by user input (this can be done by hand or determined by using taint analysis), and could be a file, standard input, a network stream, etc. Symbolic execution is a way to execute programs using symbolic variables instead of concrete values. The good news is that we do not have to understand them, we need only to reverse them! Symbolic execution They contain a lot of arithmetical and logical operations on registration data, and they are very difficult to understand. This is because I did not have to reverse them. You may notice that I provided code for the main procedure, but not for the helper functions like get_license_type, compute_customer_number, and so on. I don't know!Īnyway, this is the big picture of the registration validation functions, and this is pretty boring. Don't ask me why the protection is not completely server side but involves static tables, version checks and things like that. The version check is done by making an HTTP request to a specific page that returns a page having only the last version number of the software. As a note for the reader: most of them have been purged of uninteresting details, for the sake of simplicity.Įnum result_t check_registration ( int serial, int customer_num, const char * mail ) Here are the main variables and types used in the validation process. When I collected the most interesting functions, I tried to understand the high level flow and the simpler functions. For example, if you think a variable contains the serial, break with the debugger and see if it is the case.
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