So for a random password picked from 72 character alphabet (capital/regular letters, 0-9, 10 punctuation chars) - 5 characters would be too short, but 6 might b

So for a random password picked from 72 character alphabet (capital/regular letters, 0-9, 10 punctuation chars) - 5 characters would be too short, but 6 might be safe? (log2(72^5) < 31, log2(72^7) ~ 37). To go past 64,you'd want 11 characters. Ed: and to take the pathological case of "classic" hashes, 50 billion guesses pr second - is (almost) equivalent to 36 bits of entropy pr second. If your password is 37 bits, on average it'll be found in one second - for certain in two. If you want to aim for, say a hundred years (today), that should be about 32 bits (Log2(100 * 365.25 * 24 * 3600). So 37+32 = 69 - which is about 12 random characters from an alphabet of 70, if my math is right. Do note: random characters. Still, a 50% to find in 100 years, 25% in 50, 12.5% in 25, 6.25% in 12.5... Still like 1 in a 100 passwords in just 3? years time. So if someone has millions of secure passwords [to crack ] ... You might want more entropy still [in the entire population] .