On 6/8/12 16:05 , Alec Muffett wrote: >> Does anybody have a good URL explaining that idea? It's been >> kicking around for many years. I've never seen a convincing >> writeup. > > I've tried to do that in another mail - it's in the realms of > philosophy more than strategy; like if you're a really security-aware > person and take great care you can probably stretch the useful life > of a password out to _years_ - but how typical are *you* in that > instance?
I have a slide in a presentation I give about oncea year that goes something like: How good does a password/phrase have to be in order to protect against brute-force or dictionary attacks against the password itself? ● Entropy in language. – A typical english sentence has 1.2 bits of entropy per character, you need 107 characters to get a statistically random md5 hash. – Using totally random english characters you need 28 characters. – Using a random distribution of all 95 printable ascii characters you need 20 characters. ● Observation, good passwords are hard to come by. >> Does your bank request/require that you change the PIN on your ATM >> card every few months? > > ATM cards are not passwords, they are a coarse form of two-factor > authentication - You have the card, you have the PIN. > > You have to possess both in order to transact - at least in in > theory. > > Compare that with the secrecy surrounding the CVV - the "last three > digits on the number on the back of the card" which you are "not > meant to tell anyone" and which _will_ be different if your card is > lost/stolen and reissued. > > Now _that_ is a password. > >> Security is a tradeoff. I think there are two cases for passwords. >> I'll call them important and junk. I'm willing to store the junk >> ones in a file or piece of paper that I'm careful with. I have to >> memorize the important ones. > > You know, that's not bad. I am pro-paper for long passwords. I am > even-more pro "password safes". > >> I'm only smart enough to memorize a few good passwords. If I >> change them every few months, they will be less good, or fewer of >> them. > > It's harder as we get old. Use technology to aid with the heavy > lifting. :-) > > -a > > > >
