You can reverse engineer to your heart's content using whatever you like, provided you didn't "acquire" the original source code. Given the binary, there's nothing to legally prevent you from using or creating tools to convert machine code to assembler code and then find patterns that you can disassemble into compilable source code.

Now redistributing that code might maybe possibly get you into hot water, but to find out you'll need to go through a trial. So you use your disassembled source to learn the algorithm, then reimplement it in your own style. Now you're not even in the gray with respect to the original source.