- #USABLER SERIAL NUMBER FOR KJAMS SERIAL NUMBERS#
- #USABLER SERIAL NUMBER FOR KJAMS GENERATOR#
- #USABLER SERIAL NUMBER FOR KJAMS REGISTRATION#
- #USABLER SERIAL NUMBER FOR KJAMS PRO#
- #USABLER SERIAL NUMBER FOR KJAMS SOFTWARE#
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
#USABLER SERIAL NUMBER FOR KJAMS REGISTRATION#
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. validate your beliefs with the debugger if possible.follow cross references of data and functions to expand your collection.change data types when you are sure they are wrong: use structs and arrays in case of aggregates.similarly, rename data whenever you find it interesting.A name like license_validation_unknown_8 is always better than a default like sub_46fa39 always rename functions that uses interesting data, even if you don't know precisely what they do.I only kept in mind some simple rules, while going forward: You can find many other articles on the web that can guide you through basic reversing techniques with IDA Pro. Let me skip the first part, since it is not very interesting.
#USABLER SERIAL NUMBER FOR KJAMS GENERATOR#
The actual key generator was a simple WPF application. For the last part I used KLEE symbolic virtual machine under Linux, gcc compiler and some bash scripting.
#USABLER SERIAL NUMBER FOR KJAMS PRO#
To do this I used IDA Pro with Hex-Rays decompiler, and the WinDbg debugger. Tools of the tradeįirst steps in the reversing are devoted to find all the interesting functions to analyze. When started it presents a nag screen asking for a registration composed by: customer number, serial number and a mail address.
#USABLER SERIAL NUMBER FOR KJAMS SOFTWARE#
The software is an x86 executable, with no anti-debugging, nor anti-reversing techniques. We will concentrate our thoughts on the key-generator itself: that is the most interesting part.
We are not going to follow all the details on the reversing part, since you cannot reproduce them on your own. In this post we are going to take a look at the steps I followed to reverse the serial validation process and to make a key generator using KLEE symbolic virtual machine. My goal is instead to study a real case of serial number validation, and to highlight its weaknesses. Since my purpose is to not damage the company developing the software, I will not mention the name of the software, nor I will publish the final key generator in binary form, nor its source code. The story the user has to follow is pretty common: download the trial, pay, get the serial number, use it in the annoying nag screen to get the fully functional version of the software.
#USABLER SERIAL NUMBER FOR KJAMS SERIAL NUMBERS#
In the past weeks I enjoyed working on reversing a piece of software (don't ask me the name), to study how serial numbers are validated. By Michele "brt_device" Bertasi Category reverse-engineering Tags reverse-engineering symbolic execution Introduction
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