One final note: I've got a timeframe for 2^69 operations. Given a 4GHz processor and assuming that one operation can be undertaken every clock cycle, it will take 2^37 seconds (since 4GHz = 2^32 Hz). That's a little more than 4355 years, and I'm perversely counting leap years. Assuming you can turn this into a distributed algorithm; if you've got a shitload of money, you can parallelize the process to your hearts content and crack it in significantly less time. Although I'd recommend waiting a while: according to (a simplified version of) Moore's Law (processor speeds double every 18 months; Moore actually said something else very closely related), get 1024 processors in a little more than 15 years and you'll be able to do it in a day and a half.