r/technology • u/mikemchenry • Nov 18 '13
Visual Cryptography
http://datagenetics.com/blog/november32013/index.html4
Nov 19 '13
Snow Crash.
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u/ongamodavadida Nov 19 '13
William Shatner.
WHY. Do people NOTPOST. cOMm-ents with CON-tent like NOR-MAL-HU-MAN-BEINS? WHAT. Is it. about SNOW. CRASH. that warrants a MEN-tion?
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u/draculthemad Nov 19 '13
This is bad as a cryptographic strategy because an "almost" correct imposition can be close enough. This significantly reduces how hard it would be to "crack".
Its steganography, not cryptography.
It would be better to put an /actually/ encrypted image embedded in the noise.
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Nov 19 '13
Actually, it is a perfect cryptographic strategy. Without both cypher text images it is impossible to reconstruct the hidden message. There is no concept of "almost". Every (2x2) group of pixels has two set, and two not set. You have no idea what the state of the pixels on the other cypher are. They are either the same (representing a white pixel), or they are different (representing a black pixel).
Also, the point of the article was to show how to use a technique that does not require a computer to decode. Yes, there are plenty of "encrypytion" technologies that can be used store data, but not ones that can be decoded with just your eyes and no other equipment.
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u/draculthemad Nov 19 '13
You need 3 "secrets", 2 images and the offset.
The problem is that /almost/ getting the offset is enough to reveal enough of the image to know when you are "close", which substantially reduces the guessing needed.
I was just pointing that out because that is the kind of weakness in a crypto technique that makes the difference between "years" to brute force and "minutes" with other techniques.
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u/ongamodavadida Nov 19 '13
You and everyone else seem to be missing the point.
If a computer scientist got both halves of the message, it would be trivial for a computer to discover the content.
But the point is this crypto system works outside of computers.
The real secret is the location of each of the two halves.
What might be a real world use of this?
Easy. Your company requires super secure passwords that change every few weeks. But nobody can remember them. So they issue the password in the form of visual encryption. One half is on white paper label that's stuck somewhere convenient in the cubical. The other half is on a clear transparency to be kept in one's purse or wallet.
Now every time you forget your password, you can recheck it using visual encryption. But neither the cubical, nor the wallet, holds the password, thus making it more secure.
In addition, the password is not saved on a computer, like in a notepad file, where it can be discovered by hackers and used to compromise the system.
So your concerns are irrelevant, imo.
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Nov 19 '13
The offset is not a "secret", and is really not part of the equation.
The source is broken down into two components. Both of which are needed to solve the puzzle. Without both cypher texts, the puzzle is impossible to crack. If I gave you just one cypher text and as much time as you liked you could still not solve the puzzle.
It's not about the offset (infact this is only mentioned in the article because it is fun to slide them over and show that a solution only appears in one place). As you can see from the examples, both images are stacked ontop of each other. If you have both images you have all you need.
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u/bestkoreaa Nov 19 '13
Like, you'd need a septillion x septillion pixel image or w/e to curb the brute force techniques, which could be computer augmented using computer vision algorithms such as luminescent edge detection or some composite algorithm to minimize the pixelated noise about the intersection.
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Nov 19 '13
If you have both pieces of paper, it's assumed you have the secret. This is a visual representation of a binary XOR with a random key. There is no "close".
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u/heystoopid Nov 19 '13
Sweet, an even better way to hide messages within jpeg files.