It's the #1 program for brute forcing keys. The first version has been reviewed by many and is easier to read the code. If we're talking about so much money, I'd spare a part of my day on looking how it works.

o_e_l_e_o provided you the up-to-date version of that project. Its first version is discontinued, but both do what you want. Good luck, I hope you manage to recover your bitcoins!