How difficult is it to crack keys of different length?
The longer is the key, the more difficult it is to crack it. For example, a 40-bit key can be easily cracked within a couple of days by anyone of us using brute-force on a modern home computer. But to crack a 64-bit key you need to join powers of many computers in the internet, and all the process will take some months. And as for 129-bit keys, no one can crack them at all: neither all the computers in the world working all at once, nor Microsoft or FSB (provided that they don’t have new secret technologies, which are unfamiliar to public science).
