S-Box Analyser

S-Box Analyser is a toolkit to analyse and study the properties of any given substitution boxes.

Consider Data Encryption Standard, which was secure for around 18 years until linear cryptanalysis was developed to break the cipher. The S-boxes of DES, however, haven't been released officially yet. Hence, a tool is needed to sudy and analyse substitution boxes.

Using the look-up table of an S-Box, S-Box Analyser gets the following properties for every out-bit boolean function:

• Alegbraic Normal Form
• Truth Table
• Sequence
• Walsh Hamadard Coefficients
• Non-linearity
• Degree
• Terms present in the boolean function

In the recent years, lightweight ciphers like PRESENT have emerged as trend, which focus on easy hardware implementation, beside the security aspects. A new technique to develop secure S-boxes is using Qausi-groups.

The update includes the crypt-analysis of Quasi-groups and results to verify the security of Q-S-boxes.

Table of Contents

• main.py : Gateway to the toolkit.
• qsbox_main.py: Q-S-box analyser.
• properties.py : A place where all properties are being calculated.
• tables : Where one stores the look-up tables.
• results: The analysis reports for every substitution box.

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Setting up the thing

1. Place the S-Box look-up tables in tables named as sbox_[number].txt as already done for DES.
2. Run python main.py
3. The required results will be stored in results as sbox_[number].txt

Note:

• The files in tables might have different structure. Make sure to change line 132 of properties.py accordingly.
• The digits in each term denote the subscript of variable. Presence of '0' denotes 1 in the boolean function. Thus, Y_i is denoted by i.
• The txt files already included here are for the DES S-Boxes. Make sure to delete the previous files before analysing new S-Boxes.

Using the Code

Using the script is pretty simple. User can use main.py to operate on the toolkit through shell. Alternatively, one can import the properties module to study specific properties.

import properties

with open("sbox_analyser/tables/sbox_1.txt", 'r') as table:
	look_up = table.read()
look_up = look_up.split()

rows = [ look_up[17:33], look_up[34:50], look_up[51:67], look_up[68:84] ] #Should be changed according to format of txt.

fn_map = properties.function_generate(rows)

for i in xrange(OUT):
    print 'X' + str(i) + '\n:'
    print fn_map[i]

Version: 1.1

To-DO:

• LFSR Analyser
• Q-S-box Generator

Contribution

Feel free to report errors and submit pull requests. Contributions are welcome.