# Tag Info

Accepted

### Understanding the wide trail design strategy

Given the importance of the wide-trail strategy in modern symmetric-key cryptography, this question really deserves an answer (and a much better score). Since nobody else has tried, I'll give a brief ...
• 1,786
Accepted

### Why is the DES s-box non-linear? Why does it make the cracking of the cipher more difficult?

It is of course possible to write DES or any block cipher as a system of non-linear equations involving the plaintext bits, the ciphertext bits, and the key bits, which hold with probability 1. In ...
• 4,345
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### Selection of rotation constants in ARX design

Leaving besides that the designers (NSA) of Simon and Speck did not provide an initial design rational for their ciphers/parameter choices, they added some notes later after pressure from the ...
• 116
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### Does hashing require non-linearity?

Does hashing require non-linear components as well? Yes How would a hash built from a linear psuedo-random permutation be vulnerable to collision/preimage search? You could find a preimage by ...
• 134k
Accepted

• 1,786

• 16.7k
Accepted

### Why is not there any ideal S-Box?

It is important to understand that although a very large random function will only have linear biases with very low probability, this is simply not true of small random functions. If you choose a ...
Accepted

### Non Linearity of huge Sbox

Table construction would require 148 Exabytes of RAM, so it would be hard to store all at once. This also means that you can't have a predefined S box that you might have developed either to be a ...
• 14k
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### When it comes to linear cryptanalysis, is there always a key that could work for every possible input/output?

Regarding your first question, we assume (for known plaintext attacks such as Linear cryptanalysis) that we can obtain a large number of inputs and the corresponding outputs under the unknown key. The ...
• 16.7k
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### How do you calculate the linear approximation of an S-BOX?

You might want to check out this stackoverflow question: What is Bit Masking? Basically, the mask selects certain bits from the words, where a word is a vector (a row) of bits. The input mask selects ...
• 19.3k
Accepted

### Compression function cryptanalysis

Are there any standard/general techniques for determining an unknown compression function, given the input-output pairs? This appears to fall under the realm of reverse-engineering rather than ...
• 19.3k
Accepted

### Correlation of linear trail

This is due to the modelling approach called Markov Ciphers, by Jim Massey (I think). Basically the hypothesis is that round by round independence applies and correlations can be concatenated by ...
• 16.7k
Let's start with the basics: a bijective 4×4 bit S-box is a permutation of the set $\{0,1\}^4$ of 4-bit bitstrings. These bitstrings can be viewed as the binary representations of the integers ...