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Visual cryptography Anonymous 08/10/2017 (Thu) 12:05:58 [Preview] No. 10676
This is pretty cool. Wish I had e a program that could help me print things that can only be decoded with another transparent layer.

Anonymous 08/10/2017 (Thu) 12:21:45 [Preview] No. 10678 del

Anonymous 08/11/2017 (Fri) 22:39:26 [Preview] No. 10691 del

Hey. Can you make it work with multiple images?

Like. Aline it to the left. Get one logo. Aline it 3/4s right get another?

Anonymous 08/12/2017 (Sat) 16:57:02 [Preview] No. 10697 del
Sure, it's just a simple equation. In the pictured image it's a mere (g.field) sum. To have multiple resulting plaintexts you would add another equation to the system.

Say A and B are the images, x and y the ciphertext and keystream (in F(2^n)), then the pictured example is just a trivial:

A = x + y

To also have B, you would add another constraint, say:

B = (x << t) + (y % 2^(n-t))

Where t is the offset for ("3/4 to the right").

Strictly speaking this would not exactly describe the pictured example, because there the displacement is not linear but 2-dimensional, but we can sidestep that by instead considering A(i) and B(i) (and x(i) and y(i)) for each "i" pixel row in the images.

If you keep adding constraints you might eventually make the system unsolvable, but for two offset images it's pretty much trivial.

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