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violate as a recommendation still.
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If you're in a corporate workplace, in particular,
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and you're being required by the system administrators
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to change your password every month, maybe every three months,
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six months, every year perhaps, that's not generally recommended anymore,
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even though not too long ago, it did feel like, sound like a best practice.
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But why is this not recommended anymore, to have you forcibly
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change your password periodically, like every few months?
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AUDIENCE: Because the password will be easily forgotten
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and be more vulnerable to brute force attacks.
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DAVID MALAN: Why would it be more vulnerable?
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AUDIENCE: Because the hackers can get access to all passwords
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and get hints about the new password.
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DAVID MALAN: OK.
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So yes, one danger of forcing you and me to change our password too frequently
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is that you and I do not tend to exert much effort when
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we're required to do so.
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For instance, if my password today is, for instance, password 1, well,
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you know what my password might be in three months?
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Password 2 or in another three months, password 3.
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You and I might exert the minimal amount of energy
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to change the password so that we meet the company's requirements
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but so that it's not too hard for you and me to remember
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what the new password is.
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And so indeed, if information about my past passwords leaks out
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and some adversary sees, oh, well, wait a minute,
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your password was password 2 last month, I'm
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just going to guess heuristically that this month it's password 3.
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We might indeed be leaking information.
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What's another reason that you might not want
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to require humans to change their passwords arbitrarily
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on some schedule like this?
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AUDIENCE: We keep forgetting our passwords,
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too, if we change it too frequently.
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So that is not a good practice for a website.
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DAVID MALAN: Exactly.
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If you make me change my password too frequently,
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honestly, I'm probably going to forget what my next password is
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because I'm going to get confused with last month's
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or the previous months or the like.
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And so there's these sociological effects on us humans,
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just being human, not being very good at remembering not only the first password
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you made me choose that's very complex, but the second and the third as well.
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And so generally, you should not come up with such a scheme anymore because
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of these adverse side effects.
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And how about one more recommendation here?
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"Verifiers shall implement a rate-limiting mechanism
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that effectively limits the number of failed authentication attempts that can
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be made on the subscriber's account."
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Now, what do we mean by this?
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Well, odds are this is something you yourselves
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might have experienced if, for instance, you forgot your password
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or you kept typing it slightly wrong.
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Maybe your phone screen was wet so it wasn't
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registering your fingertips properly.
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It turns out you can lock yourself out of your own phone.
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And you might have, in fact, seen something like this on iPhone.
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Android has a similar screen, if, for instance, you
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type in the wrong passcode 10 times in a row.
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The presumption, by Apple and Google and others, is that if after 10 times
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you still haven't inputted your password correctly,
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it's probably a higher probability that you are not David,
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that you are not you, but rather it's someone else who has taken your phone,
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stolen your phone, and is trying to get into it.
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Now that's not always the case.
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You can imagine situations where you just were being absent minded.
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You were half asleep.
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Maybe you weren't really focusing on it, and you locked yourself out.
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And so there, too is, again, a trade off between usability and security.
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But the higher probability event after 10 wrong attempts
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probably tends to be that it's an adversary trying to get in and not you.
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But what's the point of this?
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Beyond annoying the adversary and maybe more significantly,
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really annoying you when it happens by accident, what this effectively does
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is it slows the adversary down.
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In other words, it increases the cost of this attack to the adversary.
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Why?
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Well, we saw a moment ago that a smart adversary
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who knows a little bit of Python code and steals your phone
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can try 10,000 possible passwords in just less than a second.
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However, if you now slow them down by having this feature
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on your iPhone or Android device that pumps the brakes, so to speak,
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that lets the adversary try no more than 10 at a time,
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that's significantly slows them down.
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Now they might have to spend at least 10 seconds, 20 seconds, an hour, a day,
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or longer, especially since what Android and iPhone also
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do is they tend to increase this time limit.
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The first time you mess up, it's 1 minute.
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If you mess up another 10 times, it's now 2 minutes, maybe 5 minutes,
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maybe 10 minutes.
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Maybe the phone even deletes itself, wipes itself,
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if that, too, is a feature that you or your company has enabled.
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So again, the right way to think about this, beyond the usability trade off,
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is that we're just trying to raise the bar to the adversary.
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We're trying to make it more expensive, more costly,
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maybe more risky to the adversary by slowing them down.
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And by more risky I mean if this is like a Hollywood moment,
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and someone's just stolen the phone from your table at Starbucks or a coffee
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shop, they've plugged it into their laptop--
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they're trying desperately to crack into it before you come back to the table--
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