HashMask - Another (More Secure) Experiment in Password Masking

http://lab.arc90.com/2009/07/hashmask.php

by umbrae • 17 years ago

15 31 17 years ago

lab.arc90.com

Nycto• 17 years ago

I was beginning to get perturbed by the inundation of password fields lately, but I actually really like this one. However, I think that it would be more effective as a browser plug-in than a site feature.

apgwoz• 17 years ago

I agree. Different implementations will undoubtably use a different visualization technique making it hard to recognize at all the different sites. Though in theory this is a non issue because everyone uses a different password per site, right?

slmbrhrt• 17 years ago

Right, at a glance you could see if someone used the same password in more than one place. Of course, you could circumvent the whole issue by pairing the url with the password to generate the hash.

tptacek10• 17 years ago

No, this is retarded; the "unique nonreversable visualization" is trivially attacked offline by brute forcing with a dictionary of passwords. It's just the SHA1 of your password; fundamentally no different from tacking /etc/shadow to your password field as you type.

It wouldn't be retarded if it wasn't expending a lot of effort (and confusing the hell out of users) to get to that bad destination. But that's what it does.

When you consider "solutions" to this "problem", model it against an adversary with a camera.

The author of this post means well, but just masking the password characters, like every secure system has done for the past couple decades, remains the right answer.

cstejerean• 17 years ago

How often do you type your password next to an adversary with a camera?

tptacek10• 17 years ago

I did it about 50 times today. I'm a building full of cameras. Tell me, how often do you sweep the surrounding area for cameras before you log in somewhere? Thought so. How many times have you ever logged into something from an airport? Ever hear about the Microsoft Blue Hat talks about the pen testers who collect credentials at Sea-Tac?

People just like memes. They're fun to talk about. I promise you there are 1,000 better problems for you to tackle in your app than the suboptimality of password masking. This guy managed not only to waste time, but also to promote an actively evil security extension.

thaumaturgy• 17 years ago

The goal regardless is to not provide a visual clue to an eavesdropper which they could use discover your password.

I actually don't think the idea of this is all that terrible, just that the implementation isn't right. For example, I can't think of a reason why the representation needs to be unique -- the user would only need a clue if their password is the wrong length or if they likely have a typo. Also, the specific representation used is too resource-intensive; three colored boxes would work just as well.

Still, even if the system returned hundreds of possible passwords for a given hash, and even if it wasn't resource-intensive, it's still providing clues to a third party, which you don't generally want to do. You're still dramatically decreasing their search space.

EDIT: On second thought, there might be a way to make this a little less horrible. If you assume that the user will generally be very close to correct in typing their password, then you could tune a function that would produce dramatically different results for similar passwords, and similar results for dramatically different passwords -- a kind of inverted hash function. Such a function probably already exists, I'm just not familiar with it. If you did that, and completely obscured what the user was typing, so that an eavesdropper couldn't tell the length of the password, then you might be increasing the search space compared to simply displaying asterisks.

umbrae2• 17 years ago

Well, as the author, I feel I better defend myself here.

A: It only uses the first 20 bytes of the hash. You could narrow it down from this if you were really determined, but you'd not be able to reverse it.

B: The visualization of the sparkline doesn't have the fidelity to determine between characters 6 and 7. So you'd have a range of possible characters.

C: The alternative being suggested by Jakob Nielsen is no masking at all ( http://www.useit.com/alertbox/passwords.html ) - which is less secure? I know this isn't the best argument, but it still is -an- argument.

With that out of the way, my paranoid mind agrees with you in this context: just masking the passwords is the more secure solution. But that doesn't mean that experiments to provide a more usable approach with (arguably) equal security should be avoided.

tptacek10• 17 years ago

(a) This sentence doesn't make any sense. You can't "reverse" full SHA1 any more than you can "reverse" truncated SHA1. And SHA1 hashes are only 20 bytes long. Reversing isn't the attack.

(b) The goal of the attack isn't to magically conjure the password; it's to magically conjure a searchlist of several tens of passwords, which is a game-changing improvement over a searchlist of, say, 72^8 passwords, or even tens of thousands of dictionary words.

Good on you for a finding an application for visualizing a SHA1 hash. You score maximum points for cleverness. But now you should retire this idea.

lhorie2• 17 years ago

>> model it against an adversary with a camera.

Which can record your hands? :)

I figure that the offline dictionary attack could be foiled if this was a Firefox extension that generated a random salt on installation. (of course, this doesn't work if you want to play WOW on an Internet Cafe)

My main reaction to the experiment is that I don't know many people who touch type (at least when it comes to their password): I've had people accidentally type their password on the username field in front of me countless times because they weren't even looking at the screen.

I don't see why I should worry about big brother FUD when I could embarrass myself any time by accidentally pressing caps lock instead of tab.

tptacek10• 17 years ago

Another thing I love about this discussion is the intimation ("big brother") that in order to get a picture of my screen, you have to be the NSA. And not, you know, some jackass with a camera.

paulgb• 17 years ago

If the attacker had a video camera and the victim was a slow enough typer (I'm thinking hunt-and-pecker), brute force wouldn't even be necessary. You could incrementally build up a string that matched the password as each letter was typed using the hash generated after each letter is typed.

Fidelity of the graphs wouldn't matter at this point, you would just take the closest match and backtrack if necessary.

tptacek10• 17 years ago

Oh wow, I didn't even notice that it generated graphs on a keystroke/timer (though, I mean, duh). Wow, is this bad. Number of mask dots, 2 midpoint colors, and the final color; how many passwords in any dictionary does that reduce to?

chaosmachine• 17 years ago

This is neat, I like it better than the last one. I would try to come up with a more lossy version. Maybe something that hashes to one of 50 animal icons. The algorithm should be good enough that any one-letter-off typo never results in the same icon. More secure, and easier to remember.

DanielStraight• 17 years ago

I don't understand. I thought the point was that unmasking would make typing more accurate, not that after you had already typed it, you'd be able to confirm what you had typed. I don't see the point in that at all.

TweedHeads2• 17 years ago

Wow, besides its functionality or not, it is a really interesting approach to solving a problem.

Kudos for imagination.

Back to the initial problem, after successive attempts you may remember the shape and colors, problem is, most business complain new users can't remember their passwords after registering, so there won't be a second time.

The only way of better remembering something is by viewing it.

TweedHeads2• 17 years ago

Tip: instead of the himalayas try using a beachball.

HashMask - Another (More Secure) Experiment in Password Masking

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