Slashdot Mirror
Scientists Release Working Prototype Of CAPTCHA-Based Password Assistant
An anonymous reader writes "Last year Slashdot ran a story on scientists from the Max-Planck-Institute for Physics of Complex Systems in Dresden, Germany developing a novel method to improve password security. A strong long password is split in two parts; the first part is memorized by a human, and the second part is stored as a CAPTCHA-like image of a chaotic lattice system. Today, after a year of work, the same group at Max Planck Institute released a working prototype online, where everybody can try this technology to encrypt files (Java plugin required)."
Absolutely - I couldn't believe the irony of this great security solution requesting full access to my machine with a self-signed certificate. I wonder if this actually a psychology experiment to show that even when people are thinking about security that they're still willing to give up the keys to the kingdom as long as you ask nicely and state that you're a "security researcher".
Slashdot comments usually contain at least a few insightful comments, but so far people have been going for wisecracks and low-hanging fruit.
Yes, using a self-signed certificate in a security product is stupid. Yes, trusting physicists to come up with a good encryption scheme is like hiring a plumber to do heart bypass surgery (I am a physicist). But those are boring criticisms. A more interesting question: is the basic idea actually any good?
If you play with it, it looks like it boils down to using a short easy password to generate a chaotic bit pattern; this bit pattern is XORed against a Captcha image. The result is easy for humans to read. If you try to decrypt with the wrong password, you get a different chaotic bit pattern that can't be read. But a computer has to do a lot of work to figure out if each bit pattern contains readable text or not.
The goal here is not to increase the entropy of the password, or to use an asymmetric algorithm that's much easier to encode than decode. Instead, they're trying to make each decryption attempt require enough compute cycles that it's impractical to brute-force even a short password.
The obvious direct attack is to write a very good, very fast captcha detector. It doesn't actually have to be able to *read* the captcha at all: it just has to be able to filter out "obviously doesn't contain text" from "probably contains text", and present the likely candidates to a human for final analysis. Some sort of noisy edge detection algorithm might work well.
If you hate writing computer vision algorithms, a simple Mechanical Turk approach might also work. If you presented a full-screen grid of 100 candidate decryptions to a human, they could probably identify one that contains text in a couple of seconds. A single human should be able to complete an English dictionary attack in a day.
There are too many oddities for me to try out the service, sorry.
1. The service isn't hosted on a .edu domain.
2. The about page makes a remarkably strong and vague claim for a group of scientists: "We are currently the strongest online encryption service available on the Internet."
3. The story was submitted anonymously rather than with a "full disclosure" warning.
4. There's no link on the web site to any supporting institutions, grants, or anything like that, even though the summary twice mentions the Max Planck Institute.
5. The unsigned software wants full access to my machine.
For all I know, this is an elaborate ruse to get a few poor saps to run untrusted code. I have nothing but the web site's word and the word of an anonymous commenter to go on balanced against the above weirdness, so I'm going to play it safe and move on.
As for you, "Konstantin," perhaps you're just a weird person, but there are way too many oddities for me to simply believe that you're the K. Kladko from the paper.
1. Your grammar and style are remarkably informal for an academic. You write like a teenager. /. comments about their work, or if they do their posts are highly informative (eg. The Bad Astronomer).
2. You use way too many smilies for a security researcher.
3. You sign your name while posting anonymously--just sign up for an account already.
4. You expect me to run untrusted code on my machine as a security researcher just because you say, "Please trust us". Seriously? Seriously? (It bears repeating.)
5. You're making lots of comments here. Usually scientists don't make any appearance on
My strong suspicion is that you're just rather young and naive and don't have enough supervision on this project. I'm not trying the software though.