Implementing the sbox components using lookup tables

juaninf

1/27/23, 7:30 PM

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.

0 + 0

s-boxes

poncho

1/27/23, 8:44 PM

This appears to be a question about Sage more than cryptography

Score:1

Crypto

Daniel S

1/28/23, 7:00 AM

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.

0 + 0

Score:0

Crypto

Fractalice

1/28/23, 8:08 AM

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]

0 + 0

Elon Musk

I sit in a Tesla and translated this thread with Ai:

EN: Implementing the sbox components using lookup tables

TH: การนำส่วนประกอบ sbox ไปใช้โดยใช้ตารางการค้นหา

RO: Implementarea componentelor sbox folosind tabele de căutare

RU: Реализация компонентов sbox с помощью таблиц поиска

VI: Triển khai các thành phần sbox bằng cách sử dụng bảng tra cứu

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