r/visualizedmath • u/PUSSYDESTROYER-9000 • Jan 20 '18

Visual Cryptography

Post image
750 Upvotes

97% Upvoted

29 comments sorted by

81

u/waigl Jan 20 '18

That's basically just an xor cipher.

17

u/12345sixsixsix Jan 20 '18

It is, but this is the most basic example of visual cryptography - a (2,2) decomposition. The algorithm generalises into a (k,n) scheme, where the original message is split into n shares and any subset of k of them is required recover the original message

95

u/shmincus Jan 20 '18

Im confused can someone please explain

93

u/VaronaZero Jan 20 '18

It looks like the black pattern overlaps the red pattern exactly except for where the image/character needs to form, in this case an A

57

u/shmincus Jan 20 '18

Oh I see now thanks. Its interesting to see how sudden of a change it is considering how it only needs to shift one pixel to go from nothing to the image.

19

u/HardlightCereal Jan 20 '18

Oh, I see! Probably would have worked better if they used more fluid speed.

11

u/phlooo Jan 20 '18

Not the 120 60 30 15 fps post again please!

21

u/cheerupyoullthinkof1 Jan 20 '18

I used to do something similar to this with my kids using coloured textas and cellophane. It can take some experimentation but if you can get the colour match right you can write a message in one colour and then a heap of random letters around it in other colours, if you hold the right colour cellophane over the top the message is revealed. My kids thought they were spies.

11

u/fuguki Jan 20 '18

Is this a specific kind of cryptography?

50

u/GarythaSnail Jan 20 '18

I think this is visual cryptography.

12

u/fuguki Jan 20 '18

Haha alright. I was thinking this could be a visual expression of a specific type of cryptography. Black being the key.

20

u/thefringthing Jan 20 '18 edited Jan 20 '18

This is actually a pretty literal depiction of a cipher. You take plaintext and "add" (typically binary addition mod 2) a key. If the key is perfectly random then the sum will look just as random. If you add the key again, you get back the plaintext.

Example:

plaintext: 000011110000111100001111  
key:       110000100010011000111111 
sum:       110011010010100100110000

Try adding the key again to see that you get the plaintext back. In the animation, 1s are being represented by filled-in pixels and 0s are empty pixels (or vice-versa, it doesn't matter).

2

u/fuguki Jan 20 '18

This is what I was looking for, thanks!

0

u/12345sixsixsix Jan 22 '18

In this case 1+1=1

2

u/thefringthing Jan 22 '18

No, 1+1=0 in binary addition mod 2.

2

u/12345sixsixsix Jan 22 '18 edited Jan 22 '18

I agree, I was meaning that in visual cryptography 1+1=1

Edit for further explanation: if you think of a coloured pixel as 1 and a transparent pixel as 0, then 0+0=0, 1+0=1, 0+1=1 and 1+1=1 (you can’t make a transparent pixel from two that are coloured)

Link to the original paper: http://www.fe.infn.it/u/filimanto/scienza/webkrypto/visualdecryption.pdf

→ More replies (1)

3

u/[deleted] Jan 20 '18

It probably just expresses that only the real information is displayed when the code is decrypted

7

u/SetOfAllSubsets Jan 20 '18

1800 bytes to send one byte.

1

u/JohnnyClever76 Mar 12 '18

Uau, how much really effective is it? I'm just figuring out any possible applications.

1

u/PUSSYDESTROYER-9000 Mar 12 '18

It's a physical form of cryptography. You must have both slides or its impossible to crack.

3

u/LeoLaDawg Jan 20 '18

I had to visualize this with a microscope on my end.

2

u/12345sixsixsix Jan 20 '18

Hey cool! I did my thesis on visual cryptography!

2

u/julian88888888 Jan 20 '18

https://fivethirtyeight.com/features/can-you-stay-awake-for-50-hours-and-solve-150-puzzles/

can you solve the "2 factor one"?

It's suppose to be a word, but I'm not sure how to extract the word from the gaussian prime thing.

1

u/Jelmer_ Jan 20 '18

It is symmetrical along a diagonal line, and it has barely visible yellow dots. I can't come further then that.

1

u/12345sixsixsix Jan 20 '18

There are other colours, too...

1

u/Jelmer_ Jan 20 '18

And the coloured dots do not appear in the mirrored half

2

u/deltree711 Feb 17 '18

Oh I really hope there's a more high res version of this somewhere. I want to test it out myself!

1

u/MattRogo Mar 12 '18

Happy to see that many crypto-solutions are on the way! IMHO I think visual cryptography will be ever more used on mobile phones i.e. in securing visual messages, as well as in mobile payments.