Linked Questions

1 vote
3 answers
7k views

How to do Hexadecimal multiplication in GF(2^8)

I'm trying to do a hexadecimal multiplication in GF(2^8). Now, I know the technique of shifting left the binary numbers in some cases, for example: 02 * 9E 0000 0010 * 1001 1110 you shift one time ...
Erik Torres's user avatar
5 votes
2 answers
1k views

Efficient pen-and-paper calculation of the Galois Field multiplication?

I have been reading on multiplication over GF for the Inverse Matrix Step in AES, and I feel like converting the hex numbers to binary, multiplying them and then doing the modifications required for ...
user3656142's user avatar
1 vote
2 answers
1k views

multiplicative inverse [duplicate]

I actually do want to know how to generate the multiplication inverse (M.I) table, I mean the calculation how the M.I been generated.. such as the M.I of 22 is 5A regarding to the table.. Do you know ...
adib hafiz's user avatar
8 votes
1 answer
32k views

Multiplication/Division in Galois Field (2^8)

I'm attempting to implement multiplication and division in $GF(2^8)$ using log and exponential tables. I'm using the exponent of 3 as my generator, using instructions from here. However I'm having ...
Jacob Wang's user avatar
4 votes
1 answer
385 views

Itoh Tsuji algorithm

I'd like to use the Itoh-Tsujii algorithm for a dynamic substitution table, but I do not get the following line: $$r\ \gets\ (p^m - 1)\,/\,(p - 1)$$ And why can $r$ be used to calculate the ...
Metalhead's user avatar
3 votes
1 answer
1k views

How are calculated numbers in AES S-box?

I have a problem calculating the 0x02 value of the AES S-Box. I followed the steps descibed in “How are the AES S-Boxes calculated?”, but my answer is not correct. ...
osemec's user avatar
  • 147
2 votes
1 answer
774 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). ...
Mithil's user avatar
  • 23
1 vote
1 answer
1k views

Inversion in $GF(2^8)$ AES [duplicate]

I was wondering how you would calculate the S-box in AES. I found that you have to calculate the inverse of the polynomials in $GF(2^8)$. I found out that to calculate the inverse, you have to use the ...
NemtAES's user avatar
  • 23
1 vote
1 answer
5k views

Calculating the multiplicative inverse of a number in $GF(2^n)$ where $n > 8$

Suppose that: We have a polynomial $g(x)$ of degree $n$. $n > 8$. $q$ is the multiplicative inverse of $p$ in $G(2^n)$ modulo $g(x)$. If $p = 0$, then $q = 0$. This could be used: As a non-...
Melab's user avatar
  • 3,655
1 vote
1 answer
6k views

Multiplicative Inverse in AES [duplicate]

I want to calculate the S-box for AES. But I have a problem with the multiplicative inverse step. For example, the inverse of 95 is ...
user39534's user avatar
1 vote
0 answers
484 views

How to find multiplicative inverse of a hexadecimal number in the finite field GF(2^8)? [duplicate]

I am new to cryptography. As I was reading a note regarding S-box construction, I found a step mentioning multiplicative inverse of a number in the finite field GF(2^8). I couldn't understand it!! Can ...
Salini's user avatar
  • 11
0 votes
0 answers
89 views

Calculating the inverse for a Rijndael s-box [duplicate]

I want to calculate a Rijndael S-box but something went wrong. How can I calculate the inverse? In the following is my approach: given: $f(x)=x^8+x^4+x^3+x+1 \rightarrow$ binary: 100011011 0x12 = ...
Larsus's user avatar
  • 33