Six really random words -- not a sentence -- gives you pretty good security. Six words chosen from this list http://world.std.com/~reinhold/diceware.wordlist.

Six really random words -- not a sentence -- gives you pretty good security. Six words chosen from this list http://world.std.com/~reinhold/diceware.wordlist.asc http://world.std.com/~reinhold/diceware.wordlist.asc truly at random gives you almost 80 bits of entropy. And six random words are easier to remember than 16 totally random letters. EDIT seriously, 221073919720733357899776 is a really big search space. If you have a computer that can search a billion per second, it's going to take 1000 computers 1000 years to catalog just 14% of the search space.