To all the people saying 2^256, please know that it's actually 2^160 to brute force a bitcoin address. You don't need to find the exact private key, you just need to find another key which collides with the hash to form the same address. Did you know that for any given bitcoin address, you can expect there to be roughly 2^96 different public keys which are valid for that address.. and so you just need to generate *one* of them to be able to spend from that address.
Is it actually less than 160 since the first character has to be 1?
How many addresses can a normal computer try each second? Feel free to be generous. A trillion you say? Whoa, but ok. 2^40. How many computers on your team? Be generous. A trillion you say? Whoa, another 2^40. Wow, every second the team is trying 2^80 addresses. There are about 2^25 seconds in a year. So, that first year the team knocks down 2^105 addresses, nice. So, in the first trillion years the team will get 2^145 addresses done. Oh, darn the end of the universe is coming up and we are still short by a factor of 2^160/2^145=2^15. Oh, we're gonna need faster than normal computers and a really big team.
