Questions tagged [s-boxes]

(or substitution boxes), components in many block ciphers used to substitute parts of the data in a non-linear way. While often fixed by the algorithm (like in DES and AES), sometimes they are key-dependent (like in Blowfish).

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102 views

What are some design considerations for S-Boxes?

My studies in cryptography have been quite detailed so far, however, one area that hasn't been explained to me is how S-Boxes are typically designed. Typically, the S-boxes are provided "as is" by the ...
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313 views

Calculate the Number of active s boxes

I really want to learn how to calculate the number of active s _boxes for block cipher cryptographic algorithms. I want to do that manually after running each round of an algorithm such as LED ...
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331 views

Number of active s boxes

How can I calculate the minimum number of active s_boxes for block cipher algorithms such as present algorithm? I have read in that, but I couldn't understand the meaning of branch number.
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332 views

Simplified AES S-box multiplication - calculation error

I have a problem to calculate the S-box in S-AES. The affine transformation is defined: I read that it is a normal matrix multiplication. I chose the bits $0101$ and built the inverse $1011$. $b_0$ ...
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1answer
130 views

How many primitive cryptography operations are there? [closed]

Every cipher I've encountered seems to be built from slight variations of only three basic operations: the S-box, the P-box, and the XOR. I’m just wondering, are there any others? And if there aren'...
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313 views

AES and GOST 28147-89 “Magma” Comparison

I am trying to understand how AES is comparable to GOST 28147-89 "Magma". Like for parameters such as bit shifting and addition of the subkey to the input, which are a part of Magma, what is their ...
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2k views

Finding output given an S-box input of 8 bits

I'm given the following table: I'm told to find the output given an hexidecmal input of 2B. I know that 2B in binary = 001 01 011 So I took the first two and ...
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1answer
355 views

Security Implications of Fixed & Opposite Fixed Points of Sbox

Fixed point means when Sbox Input is equal to Sbox Output whereas Opposite Fixed Point means when Sbox Input is complement of Sbox Output. How does Fixed and Opposite Fixed Point affect the strength/ ...
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31 views

Measure Strength of Mix Mode Modular Arithmetic based Confusion Layer

Strength of sboxes is generally measured by different properties eg non linearity, fixed points etc. If confusion is provided by Mixed Mode Modular Arithmetic (eg as in IDEA), how to measure the ...
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419 views

Does the DES s-box only provide confusion, or does it also provide an avalanche effect?

In DES, does the s-box provide an avalanche effect or does it only provide confusion in the ciphertext?
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348 views

Security of the AES with a Secret S-box

In this paper they change the $AES$ S-box to a uniformly random one and answer the questions: How does the security of AES change when the S-box is changed by a secret S-box? Would it be safe to ...
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1answer
175 views

Non Linearity of huge Sbox

Sboxes provide confusion in cipher. Non Linearity measures the strength of sbox layer. In order to measure non linearity of sbox, a table is computed to measure distances with its affine functions. If ...
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1answer
1k views

AES S-box calculation

I am trying to design the s-box for AES. Quoting from Wikipedia, the algorithm for applying affine transformation in AES s-box calculation is ...
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1answer
94 views

Number of Substitution boxes

How many possible 16 bit S-boxes exist? (AES uses 8 bit substitution boxes) I first taught of calculating 128(keysize in bits)/8(bits) =16, but I believe it's wrong.
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AES s-box – How do I calculate the inverse of this field equation?

I want to implement AES algorithm,instead of LUT based S-box, but I’m stuck at point creating "Inverse of equation" during implementation. In creation of S-box I am using the following steps: ($...
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152 views

Affine of Inverse Sboxes

"All 8x8 s-boxes created using Galois Field inversion plus an Affine Transform have the same non-linearity, as the Affine Transform does not change the linear or differential properties" is what this ...
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1answer
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AES S-Box: Possible options for constant to calculate S-Box values

To calculate the values of S-Box in AES, I came across a lot of resources where constant {63} was chosen. It is said that {63} satisfies the condition of S-Box that it should not have any fixed points ...
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1answer
106 views

AES S-Box: How is value for 01 mapped to 7c?

If irreducible polynomial $m(x) = x^8+x^4+x^3+x+1$ is chosen, or even for any other value, the multiplicative inverse will not exist for $01$, as $0000 0001$ will perfectly divide $m(x) = 100011011$ ...
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152 views

number of active s-boxes in a block cipher?

How can we find the minimum number of differentially active s-boxes in a block cipher (actually a Feistel network with several input cells) in a truncated characteristic form? In a recursive ...
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AES S-Box Lookup Table Hardcoded?

From what I've looked up on various AES projects, the impression I get is the lookup table is hardcoded with the values from this Wikipedia entry page: https://en.wikipedia.org/wiki/Rijndael_S-box ...
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Building large S-Boxes from smaller ones

I would like to make an exhaustive list of all relevant techniques that have been studied in order to build a large S-Box from smaller ones. As far as I known, three structures are usually preferred: ...
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96 views

Turning an S-box into a keyed S-box

Assume that $S(x): \{0, 1\}^{n} \rightarrow \{0, 1\}^{n}$ is a good S-box. Is there anyway we can construct a keyed S-box $T(k, x): \{0, 1\}^{n} \times \{0, 1\}^{n} \rightarrow \{0, 1\}^{n}$ from it ...
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1answer
426 views

Explain the fast Walsh–Hadamard transform in simple steps or pseudocode

I've read that the fast Walsh–Hadamard transform is a way to efficiently calculate the linearity/non-linearity of an S-box. Can I get a description of it in simple steps or pseudocode that is ...
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1answer
372 views

Relying on a 4-bit S-box instead of an 8-bit one

I've discovered that generating good S-boxes with only modular addition, bitwise XOR, bitwise AND, bitwise OR, bitwise NOT, rotations, and, shifts is difficult. I figure that using them to make a good ...
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75 views

How are calculated input S-box?

a) if input 1011 = 0 1 1 1 b) if input 0110 = 1 1 0 0 my answer right?
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274 views

S-box and Side Channel Attacks

S-boxes with non-linearity greater than 112 are considered prone to side channel attacks. If a non-linear S- box with non- linearity greater than 112 (excluding bent functions with non-linearity of ...
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1answer
167 views

Are SHA-2's $\mathit{Maj}$ and $\mathit{Ch}$ functions non-linear?

SHA-2 has two functions: $\mathit{Maj}(x, y, z) = (x \land y) \oplus (y \land z) \oplus (x \land z)$ $\mathit{Ch}(x, y, z) = (x \land y) \lor (\neg x \land z)$ Are these two functions non-linear? ...
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73 views

Identification of Confusion Component in a Cipher

Confusion is a necessary component of any encryption algorithm. S-boxes play an important role in ensuring confusion. If an encryption algorithm does not use any S-box (rather some other Operations/...
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1answer
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Non-Linearity of an Sbox

Non-Linearity of an Sbox affects its resistance towards Linear Cryptanalysis. What happens, if an Sbox has low non-linearity (specially with respect to Linear Cryptanalysis)?
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152 views

Degree of a big S-box

Assume we have a big S-box (i.e. $15*15$). We have truth table of it. (so $2^{15}$ output). How can we find its degree without using Algebraic Normal Form of its Boolean functions. Or with ANF, can ...
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707 views

AES: How to create the S-box with Sage

The $Sage$ code for the AES $S-box$ is below and a link is here: Polynomial representation of the affine part of the AES S-box. An online version of $Sage$ to test this is here. I understand most of ...
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Why don't table lookups run in constant time?

The Wikipedia article on big O notation says that performing a lookup is a constant time operation. So why are lookup tables susceptible to timing attacks?
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73 views

Security of an S-box based on modular multplicative inverse

The construction of Rijndael's S-box starts with the multiplicative inverses of each number over a finite field. It seems like this is the main source of its non-linearity. I figured that modular ...
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527 views

How can we create the AES S-box using a different irreducible polynomial?

The substitution-value of input byte $\mathtt{C2}$ is $S[\mathtt{C2}]=\mathtt{2F}$. This comes from applying the Euclidean algorithm to $A(x)A^{-1}(x)\equiv 1\pmod{p(x)}$, where $A(x) = x^7+x^6+x$ (...
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What rule(s) for a good S-box is this one violating and how does it relate to non-linearity etc.?

I generated this single-cycle substitution box and I want to post it as an example for understanding what a good S-box would be like. I get the feeling that this particular one is weak. Here it is (...
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99 views

Are there any security flaws in using an involutive S-box?

I know that it is difficult to answer these questions without knowing the full scheme it would be used in, but are there any problems that could be introduced into a block cipher if an involutive S-...
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1answer
832 views

AES S-Box implementation: from a byte-by-byte to 2-bytes-by-2bytes?

The S-Box in AES encryption is a byte substitution step. Is it possible to perform the substitution 2 bytes at a time, rather than 1 byte? What are the challenges/trade-offs involved?
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What Is The Number of Active S-boxes over 5 Rounds of Fides AE cipher?

It is mention in the paper " Fides: Lightweight Authenticated Cipher with Side-Channel Resistance for Constrained Hardware" , the number of active S-boxes of Fides cipher is 22 over 5 rounds but my ...
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How are S-box calculated in S-AES?

Read the Reference for Simplified AES ( S-AES ) Q1 Explain how the S- box is constructed taking example $b_0b_1b_2b_3=1010$ What I did $\begin{bmatrix} 1 &0 &1 &1 \\ 1 &...
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645 views

How can AES-like block cipher without non-linear component be broken?

I am taking a course on block ciphers and recently I have faced up with such an exercise: if an original AES's highly non-linear Sbox is replaced by a linear substitution (see example below), how one ...
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1answer
671 views

How can one construct the weakest S-box ever?

Is it possible to come up with an NxN S-box which would have a difference distribution table with N entries of 100% probability? I am studying the properties of S-boxes and I don't quite understand ...
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Why do we keep designing new static s boxes?

As I understand s box properties, they primarily need high non linearity and low auto correlation. But most importantly for this question, they're not secret. There are many questions on this site ...
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Can a stream cipher with a big S-box create ASIC-resistance?

For a proof of work system a hash algorithm generates one pseudorandom index each round, in the same manner as RC4 and Spritz do. And it uses a bigger S-box, e.g. 2^20 numbers. The actual hash would ...
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S-box basic question

I'm trying to understand DES and a bunch of other cryptographic systems using S-Boxes. I have now a quite basic question about how Sboxes work in general. For DES, Sboxes are substituting a 6-bits ...
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How many Affine function can be made from $4 \times 4$ and $8 \times 8$ S-boxes?

The nonlinearity of an S-Box is defined as the non-linearity of its vectorial Boolean Function. Let $F$ be the hamming distance between the set of all non-constant linear combinations of component ...
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Generate ANF from SBox

Given an SBox, how can I generate its component equations (in ANF)? For example, let's say I have this SBox: 6, 4, 7, 8, 0, 5, 2, 10, 14, 3, 13, 1, 12, 15, 9, 11 Then, the equations are: $y_0 =...
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270 views

Bit slice format of 4x4 s-boxes?

I have studied bit-sliced implementation in SERPENT block cipher and I need to use this technique to implement some 4x4 s-boxes. I couldn't find any procedure to obtain bit-sliced format in any paper ...
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1answer
971 views

Construction of S-box in AES

In my introductory cryptography class. There is a line describe the construction of S-box in AES "The S-box of AES is constructed by combining a function $h(x)=x^{254}$ defined on $GF(256)$ with an ...
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468 views

How are Rijndael's S-Boxes generated?

Wikipedia: Rijndael's Forward S-box I'm writing C Code to generate S-boxes but I'm stuck. Would you mind explaining one entry of the S-box? (say for x = 0x2). ...
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AES vs DES S-boxes

I understand from the literature that the DES S-boxes were very carefully designed with the process involving exhaustive search, trial and error, and an anticipation (by 15 years) of "differential ...