Clearing my tabs: Choosing secure passwords

[mdlbear]

Schneier on Security: Choosing Secure Passwords

Ever since I wrote about the 34,000 MySpace passwords I analyzed, people have been asking how to choose secure passwords.

My piece aside, there's been a lot written on this topic over the years -- both serious and humorous -- but most of it seems to be based on anecdotal suggestions rather than actual analytic evidence. What follows is some serious advice.

The attack I'm evaluating against is an offline password-guessing attack. This attack assumes that the attacker either has a copy of your encrypted document, or a server's encrypted password file, and can try passwords as fast as he can. There are instances where this attack doesn't make sense. ATM cards, for example, are secure even though they only have a four-digit PIN, because you can't do offline password guessing. And the police are more likely to get a warrant for your Hotmail account than to bother trying to crack your e-mail password. Your encryption program's key-escrow system is almost certainly more vulnerable than your password, as is any "secret question" you've set up in case you forget your password.

Offline password guessers have gotten both fast and smart. AccessData sells Password Recovery Toolkit, or PRTK. Depending on the software it's attacking, PRTK can test up to hundreds of thousands of passwords per second, and it tests more common passwords sooner than obscure ones.

So the security of your password depends on two things: any details of the software that slow down password guessing, and in what order programs like PRTK guess different passwords.

Don't recall where I found the link for this one; probably Don Marti. Good advice in any case.