On Jan 2, 2012, at 9:10 PM, Lyndon Nerenberg wrote: >> I just went through some calculations for a (government) site that has the >> following rules: > [...] >> Under the plausible assumption that very many people will start with a string >> of digits, continue with a string of lower-case letters to reach seven >> characters, >> and then add a period, there are only ~5,000,000,000 choices. That's not >> many at >> all -- but the rules look just fine... > > 1234;lkj rolls off the fingers quite nicely, don't you think? > OK -- let's let the set of punctuation be .,; and allow seven choices for where it goes. That increases the work factor by 21 -- still not that large a space for someone with a good botnet.
The real question is what you're trying to protect. If the attacker's goal is to get *some* password, then I think he or she will get succeed, because I think that very many people will follow my assumed pattern -- enough that the attacker has a good chance of winning. Sure, some people will pick stronger ones -- but that isn't the point of the exercise. Passwords and password rules are the *enemy* to most people. --Steve Bellovin, https://www.cs.columbia.edu/~smb