# Tag Info

## Hot answers tagged visual-cryptography

11

No, you can reuse a message as often as you want with the OTP. (But never reuse the key!) What happens if you reuse a key? The attacker can xor the two encrypted messages (ciphertexts) and gets the xor of the two plaintexts. The xor of two messages is highly insecure and can be easily turned into two plaintexts with some know patterns. What happens if you ...

5

Actually, it's fairly simple: Generate an image with random pixelation; that is, each pixel is either black or white with probability 1/2. We'll call this image 1. Exclusive-or image 1 with the target to generate image 2; so that a pixel image 2 will be white if the pixels in image 1 and the target are the same (both with or both black), and black if they ...

4

The simplest form of visual cryptography use transparencies that each individually convey no recognizable information, but reveal a meaningful image when precisely aligned The basic approach for doing the same with video is using such visual cryptography to encipher each frame. That works, but (as stated in the question) requires generating two images for ...

2

A typical problem with the images regenerated by visual cryptography is that they have low contrast: when using superposed transparency, the white in the original image tends to become grey (or more precisely, 50% dithering of black and white, which is even worse from a 2D-code scanner's perspective); and there might be some white that creep in the black ...

2

Why use visual cryptography to split the QR code, and not secret-share the original data, and generate a QR code for each share instead? That way, you can scan the shares, and by combining them reconstruct the original secret.

2

The dealer is one of n participants or it should be from outside? The dealer, knows the secret as he's the one who shared it. Thereby it makes no sense to give him a share as well, unless you have a such a scheme that requires all partys to collaborate to recover the image, but then the question becomes: "Why bother secret sharing at all if the dealer could ...

2

This is string notation: $J_i^0=0^{i-1}10^{k-i}$ means i-1 consecutive 0's followed by a 1 (we don't write $1^1$) which is then followed by k-i consecutive 0's. So $0^{3}10^{4}$ is $00010000$. As for $S^t[i,x]=\langle J_i^t,x\rangle$, with $t\in \{0,1\}$ this is an inner product of $J_i^t$ with $x=(x_1,\ldots,x_k) \in \{0,1\}^k$ so in general $S^t[i,x]=x_i$ ...

2

No. As the key should be fully random - a premise that invalidates the use of an OTP in practice - that should not matter at all.

2

Something that may interest you would be a secret sharing scheme by Shamir titled Visual Cryptography. http://www.cs.nccu.edu.tw/~raylin/UndergraduateCourse/ComtenporaryCryptography/Spring2009/VisualCrypto.pdf

2

Yes, you can write a single application to reveal the hidden information as long as you know the method and they are not encrypting the messages they hide. The Wikipedia article in Steganography tools lists some information about availability as an opensource, their methods, and usege of encryption. And some information can be found on their website. For ...

2

An access structure is just a function $f:\{0,1\} ^n\to \{0,1\}$. It takes a subset of $\{1,\ldots,n\}$ as input (represented as it's characteristic vector) and returns 1 if authorized and 0 if unauthorized. Additionally, the function must be monotone, meaning that $A\subseteq B \implies f(A) \le f(B)$. The number of monotone Boolean functions over $n$ ...

1

First of all, coin tossing represents a uniform random generator. Therefore, the selections are assumed to be uniform. In order to create a share for a pixel, as you mentioned, a pixel split into two subpixels. A share for a white pixel can be $[(B|W),(B|W)]$ or $[(W|B),(W|B)]$ a black pixel can be $[(B|W),(W|B)]$ or $[(W|B),(B|W)]$, where in $[(x,y)]$, $x$...

1

There is no need for those image encryption algorithms. You can encrypt an image file, like any other sequence of bytes using standard encryption. If you really want to encrypt the pixels themselves (not recommended), you can use standard length preserving encryption, such as a four round feistel network. I've seen some image encryption papers, but they ...

1

I was just wondering if a cipher existed where a number of symbols were colored with different colors forming a cipher? What you describe is not related to cryptography, but practically boils down to a form of encoding a ciphertext. Cryptographically secure ciphers tend to programmatically output a series of bytes. How you handle and represent those bytes ...

1

I haven't seen any such implementation of a cipher. That being said, you could implement it yourself. If you take each byte in a cyphertext and put them into a bitmap, you can display each "letter" as a pixel. Remember, a byte consists of 8 bits, which can represent a number between 0 and 255. Which is one of the most common amount of colors a pixel can hold....

1

which cryptographic algorithm and which steganography technique put together will result in the most efficient, secure data? AES and DES are already a combination of separate algorithms involving multiple steps each. They are already "put together". Steganography won't add additional security because of Kerckhoffsâ€™ principles. In what way other than ...

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