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).

Filter by
Sorted by
Tagged with
1
vote
2answers
2k views

How we can calculate AES Inverse SBox?

I am trying to find out the inverse of and SBox, but in vain, I have seen multiple questions over StackExchange, But I cant be able to solve my issue. As in this question, How are the AES inverse S-...
4
votes
3answers
1k views

What's happens if we use the weakest S-BOX for AES?

I'm in research of generating Dynamic Secret S-BOX for AES based on 2 Keys (Encryption Key and *I Called S-BOX key). If (worst scenario) I randomly generate the worst S-BOX in an encryption. What ...
1
vote
1answer
482 views

how to compute the correlation between two binary vectors?

We find different equations to compute the correlation or correlation coefficient: $\begin{align*} corr &= \frac{a+d}{a+b+c+d}\\ &= \frac{(a+d) - (b+d)}{a+b+c+d}\\ &= \frac{(a+...
2
votes
0answers
122 views

Strict Avalanche Criteria in Sage

Is there any inbuilt functionality in sage to check if any S-Box satisfies Strict Avalanche Criterion or not?
1
vote
0answers
394 views

how to compute Bit Independent Criteria on a 4-bit S-box?

The idea of Bit Independence Criterion (BIC ) was introduced by Webster and Tavares . For a given set of avalanche vectors generated by complementing a single plaintext bit, all avalanche variables ...
0
votes
1answer
73 views

what is the impact of smaller bit size sbox

There are multiple S-boxes type, as DES uses 4 bit S-box and AES uses 8 bit S-box. I want to know how this effect the security?? If we use 4 bit or 8 bit. apart from the DC attack. Both provides ...
2
votes
2answers
253 views

AES alternate equation for the S-Box affine transformation

The Wikipedia article for the AES S-Box gives an alternate equation for the affine part of the S-Box transformation: $$b_{out} = (b_{in} \times 31_d) \operatorname{mod} 257_d \oplus 99_d$$ It is not ...
2
votes
1answer
404 views

AES with linear S-Box

If the AES S-Box is replaced with a linear or affine transformation, for instance the identity mapping $\sigma(x)=x$, does the cipher become entirely affine and hence trivially weak?
1
vote
2answers
116 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 ...
3
votes
3answers
400 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 ...
3
votes
1answer
382 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.
2
votes
1answer
398 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 $1011$. $b_0$ ...
4
votes
1answer
138 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'...
0
votes
1answer
421 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 ...
0
votes
1answer
3k 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 ...
5
votes
1answer
413 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/ ...
2
votes
1answer
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 ...
2
votes
3answers
661 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?
5
votes
2answers
423 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 ...
4
votes
1answer
197 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 ...
1
vote
1answer
2k 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 ...
0
votes
1answer
103 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.
5
votes
1answer
1k views

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: ($...
0
votes
1answer
178 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 ...
2
votes
1answer
136 views

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 ...
1
vote
1answer
114 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 $m(x) = 100011011$ ...
1
vote
1answer
161 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 ...
2
votes
2answers
2k views

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 ...
4
votes
2answers
168 views

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: ...
0
votes
0answers
101 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 ...
1
vote
1answer
545 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 ...
2
votes
1answer
391 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 ...
0
votes
1answer
105 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?
0
votes
1answer
330 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 ...
2
votes
1answer
185 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? ...
1
vote
1answer
79 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/...
3
votes
1answer
2k views

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)?
1
vote
1answer
167 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 ...
3
votes
2answers
884 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 ...
6
votes
3answers
1k views

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?
0
votes
0answers
76 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 ...
4
votes
2answers
579 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 $A(x) = x^7+x^6+x$ (...
2
votes
2answers
220 views

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 (...
1
vote
1answer
105 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-...
2
votes
1answer
904 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?
2
votes
1answer
107 views

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 ...
0
votes
1answer
2k views

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 &...
1
vote
2answers
754 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 ...
2
votes
1answer
754 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 ...
16
votes
2answers
1k views

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 ...