Cryptography Stack Exchange
Cryptography Stack Exchange

Questions tagged [spn]

A Substitution-Permutation-Network is a structure that has been used to create a number of different block ciphers (e.g., AES, Picollo, Present...)

Such a network takes a block of the plaintext and the key as inputs, and applies several alternating "rounds" or "layers" of substitution boxes (S-boxes) and permutation boxes (P-boxes) to produce the ciphertext block. The S-boxes and P-boxes transform (sub-)blocks of input bits into output bits. It is common for these transformations to be operations that are efficient to perform in hardware, such as exclusive or (XOR) and bitwise rotation. The key is introduced in each round, usually in the form of "round keys" derived from it. (In some designs, the S-boxes themselves depend on the key.)

36 questions
17
votes
3 answers

Why is AES not a Feistel cipher?

I am studying for an exam right now. And I wanted to make sure I got this point correct. AES is not a Feistel cipher because the operations in AES are not invertible. Is the above statement correct? If not, why isn't it a Feistel cipher?
mike
  • 273
  • 1
  • 2
  • 5
7
votes
1 answer

Linear Approximation Table of S-Box for SPN

I havejust gotten to Linear Cryptanalysis and I'm studying some material on Linear Attack's against SPN. I see here http://www.cs.bc.edu/~straubin/crypto2017/heys.pdf on page 11 that they calculate the Linear Approximation Table but I am completely…
Temirzhan
  • 217
  • 2
  • 5
6
votes
3 answers

Substitution-permutation network visualizer

I'm doing differential analysis of a toy block cipher in which I've to extract the differential characteristic of the first n-1 rounds. However, I can't do that very well as I can't see the network itself. Basically, I wonder if there is a software…
SpiderRico
  • 461
  • 6
  • 19
6
votes
2 answers

What is the diffrence between Feistel networks and SPN?

I recently read about the concept of Feistel Networks and Substitution Permutation Networks but what is exactly the difference between the two ?
blacklight
  • 581
  • 7
  • 13
5
votes
1 answer

Increase number of rounds for SPN and Feistel ciphers

Read a post on Schneiers blog (and again 2011) about increasing the number of rounds for AES from to "AES-128 at 16 rounds, AES-192 at 20 rounds, and AES-256 at 28 rounds" to raise the security. However, I did wonder where these figures came from.…
marluh
  • 63
  • 5
4
votes
1 answer

Using a round function intended for an SP network in a Feistel network?

If I use the round function from a secure SP network (such as AES) and use it in a Feistel netwok, is this a good starting point for the second cipher? My thought is "yes" because: it already has good diffusion and confusion it doubles the block…
Demi
  • 4,853
  • 1
  • 22
  • 40
4
votes
2 answers

What is the intuition behind AES or SPN?

I'm new to cryptography and have just encountered AES and SPN. I would like to know how the S-box, permutation step and the MixColumn step help improve security. It seems to me (perhaps mistakenly) that the security is provided solely by the key and…
BlackAdder
  • 408
  • 5
  • 13
3
votes
0 answers

Understanding Linear Cryptanalysis

I'm reading about the linear cryptanalysis of an SPN and I have some questions about the practicality of this. The example I'm looking at is from 3.3.3 of Stinson's Book and I believe the same example is given in these notes (pg.13 for the…
Rdrr
  • 141
  • 2
3
votes
2 answers

modified substitution permutation networks

I have a model of substitution permutation networks, modified as follows: instead of iterating $n$ times a round(each of which is composed of the key mixing phase, substitution S-BOX) and permutation), I apply the key mixing phase to the input $n$…
quaqua
  • 63
  • 3
3
votes
2 answers

Would there be any advantage in combining Feistel network and substitution-permutation network in a single cipher?

One common way to design invertible block ciphers is using a Feistel network used in for example DES and Blowfish. Another common way is a substitution-permutation network used in for example Rijndael (AES). Would there be any advantage in combining…
juhist
  • 1,643
  • 1
  • 13
  • 18
3
votes
1 answer

Midori block cipher design: importance of $S_b$ as the S-box

With a use of almost MDS the Midori cipher provides a good diffusion. But why $S_b$ is used as S-box and what is its actual importance?
Ranit
  • 31
  • 1
2
votes
1 answer

Substitution-Permutation Network (SPN) Example

I came in contact with an algorithm that deals with SPN in an example, first I'd like to give a definition of what it is: Let $l, m, $ and $N$ be positive integers, let $\pi_s: \{0,1\}^l \to \{0,1\}^l$ be a permutation, and let $\pi_p:\{1,...,lm\}…
João Víctor Melo
  • 221
  • 1
  • 10
2
votes
0 answers

ε-close to t-wise inependence of SPN (AES)

According to theorem 3.13, the 6 rounds of AES is 0.472-close to pairwise independence. It is also mentioned t-wise independence used to analyze higher order derivates attacks. it is also mentioned 3-wise indepdent permutations have a potential…
hardyrama
  • 2,288
  • 1
  • 17
  • 41
2
votes
1 answer

Definition Problem for toy SPN

I am reading Differential Attack from Stinson-Cryptography: Theory and Practice on a toy example of S-box(block Cipher) with Nr=n=m=4. I am mainly confused in the following definition Definition 3.1 : Let $\pi_S:\{0,1\}^m\rightarrow \{0,1\}^n$ be…
Kumar
  • 127
  • 7
2
votes
2 answers

Is the order of applying transformations in SP cryptosystems significant?

SP-cryptosystems Is the order of applying transformations in SP cryptosystems matter? What will change if we first apply the P-transformation and then the S-transformation? Will cryptographic strength be less? And if yes, why?
quest-lion
  • 21
  • 3
1
2 3