Should you really change your re-used passwords after a breach? Maybe not.

The news is reporting that 453,000 credentials were allegedly taken from Yahoo, and current reports say that it's probably Yahoo Voice that was compromised. If you want to know if yours is in there, it seems like the hacker website is overwhelmed at the moment, but you can search for your username/email here on a sanitized list that doesn't include the passwords.

Probably unsurprisingly, the next bit of news is that people haven't changed their hacked passwords from previous breaches. To whit, 59% of people were re-using the passwords that had previously been hacked and released to the public in the Sony breach. Which seems a bit high given the publicity, but I'm not as surprised as I maybe should be.

What I'd really like to know is how many of those people actually suffered from this password re-use. Did anyone bother to try re-using their credentials?

I'm reminded of one of my favourite security papers, "So Long, and No Thanks for the Externalities: the Rational Rejection of Security Advice by Users," by Cormac Herley. In it, he claims that many security "best" practices like changing passwords frequently are actually a waste of time for the average user, when you take into account the risks involved.

So, is changing a password after a breach one of those things that we can skip without much incident? Sadly, I don't have any definitive way to analyze how many folk were inconvenienced by their password reuse in the Sony and subsequent Yahoo breaches, but I can make a guess: If those accounts were compromised on Yahoo after the Sony breach, we'd be seeing a lot more people changing their passwords between the two. So probably at least those 59% were not inconvenienced enough to change their passwords subsequent to the breach.  That's a lot of people.

Of course, it's possible that the accounts were breached and used in a way that the owner never noticed. But if they're not noticing, are they really being inconvenienced? Probably in a global sense (i.e. spam) but maybe not in a short-term decision-making sense. Of course, we could assume that the alleged hack is a hoax using many of the previously hacked passwords from Sony, but given how easy it is to compromise web apps I'm currently assuming that the hack itself is a real thing.  In which case, that's a lot of no-change. It looks suspiciously like you're likely to be more inconvenienced taking the time to change your password than you would if you did nothing, statistically speaking.


So, should you change your password after a breach? It depends on how much you feel like rolling the dice. Failing to change their breached passwords doesn't seem to have hurt that many of the Yahoo Voice denizens, but with numbers on re-used passwords hitting the news today, it's possible we'll see more people trying this avenue of attack in the future.  Still, rather than assuming those 59% are foolish for keeping the same credentials, it's worth considering that they might have just been savvy gamblers, this time.

Will Facebook's choice of social authentication (face CAPTCHAs) lead to huge gains in facial recognition software?

Some of my friends,
for your future hacking pleasure
by Terriko.

We've actually talked about this sort of thing considerably within my research group, so it's hardly a new idea, but it's still interesting because I hadn't heard of a large scale implementation of this before: Nevermind CAPTCHA, Facebook Asks If You Know Your Friends.

They're calling it "social authentication" where rather than reading obfuscated text as in a normal CAPTCHA, you're asked to identify friends.

"Instead of showing you a traditional captcha on Facebook, one of the ways we may help verify your identity is through social authentication," writes Rice. "We will show you a few pictures of your friends and ask you to name the person in those photos. Hackers halfway across the world might know your password, but they don't know who your friends are."

Of course, that's not true at all. For many people with public profiles, flickr accounts, etc. it's pretty easy for a hacker to identify your friends. (Even easier if your would-be hacker is a jilted lover or angry sibling, but presumably those folk could also pass a regular CAPTCHA.) The key here isn't that this social authentication isn't hackable, though, it's that the hack has to be more carefully crafted to your account, and may well require a human to do the facial recognition necessary, thus slowing down the attack and doing exactly what CAPTCHAs were intended to do.

I'm curious to see how well it works in practice, though. CAPTCHAs in their current "mangled text" form relied on assumptions about the ineffectiveness computer text recognition... assumptions that have been rapidly broken as determined attackers and researchers have improved our text recognition algorithms. (Nowadays, many captchas can be bypassed with a higher than 90% success rate. Here's a link to one such paper but a websearch will turn up many others.)

Friends in costume
by Terriko.

So the interesting question to me is "Will Facebook's choice of Face CAPTCHAs lead to huge gains in facial recognition software?" -- we're well overdue for gains in that area, actually, given that law enforcement is hoping to use facial recognition to stop crime and even terrorism, but the technology is so poor right now that if they used it now they'd likely be arresting a lot of innocent folk. Facebook will lead to some great cases: What about when your friends are in costumes? Wearing different makeup? Different lighting? Different poses? Different hair?

Beyond the usual halloween costumes, my facebook friends include theatre geeks, haunted house aficionados, members of the 501st legion of Star Wars costumers and folk involved with things like the Society for Creative Anachronism. Will my friends' and acquaintances' penchant for elabourate costumes mean that I'm more secure? Or will it mean that I'll have more trouble identifying them in photos unless I've seen their standard costumes before?

Mostly I'm torn between excitement at new gains in image processing and a vague sense of unease when I contemplate the potential applications of better facial recognition software.