If you presume rrdharan generated his password as a string of random alphanumeric characters and round that to there being 64 of those, he revealed $32 / n pick

If you presume rrdharan generated his password as a string of random alphanumeric characters and round that to there being 64 of those, he revealed $32 / n pick 4$ bits of entropy. Where $n pick 4$ is the number of combinations of length 4 drawn from n. That only works if you presume his password was generated as a string of random bits though. If the password was generated as a dice-ware password [1] with 5 characters this reveals roughly 2 bits of entropy. For we know he doesn't use -, _ or nothing as his word-separator. Those 2 bits aren't included in the calculation that states his diceware password has about 65 bits of entropy though. (5 words from a list of 8000) 65 bits feels like plenty to me. [1] http://world.std.com/~reinhold/diceware.html http://world.std.com/~reinhold/diceware.html