0

Does it is possible to implement the components of a SBOX tables using lookup_tables. For example for a 4-bit SBOX it is possible to obtain the component 3 using SAGE in the following way

sage: from sage.crypto.sbox import SBox
sage: S = SBox([7,6,0,4,2,5,1,3])
sage: f3 = S.component_function(3)
sage: f3.algebraic_normal_form()
x0*x1 + x0*x2 + x0 + x2

But I need to use that component several times (lime $2^{20}$), and boolean function in SAGE with substitution are so slow. Than I think it is better to use lookup tables.

juaninf
  • 2,701
  • 2
  • 18
  • 28

2 Answers2

1

You are correct. The Boolean expressions for the components returned by Sage are not intended for efficient evaluation but rather to help the algebraic analysis of the cipher (e.g. as part of expressing bits of the round function or key schedule as a polynomial expression and calculating the degree thereof).

If you do want to collect data on the component function for a large number of inputs, again you are correct, the pre-computation of a look-up table is much more efficient.

Daniel S
  • 23,716
  • 1
  • 29
  • 67
0

f3 in your code is a Boolean function which is basically a list of True/False values.

list(f3)                                                                                                                                                                                                                                
[False, True, False, False, True, True, True, False]
Fractalice
  • 3,087
  • 12
  • 10