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Azul Plugin Index Coincidence

This plugin uses the index-coincidence package to compute the index of coincidence and search for widths which improve the index of coincidence.

The Index of Coincidence (IC) is a statistical tool used in cryptography to analyze the frequency distribution of letters in a ciphertext. It helps determine whether a cipher is monoalphabetic (e.g Caesar cipher) or polyalphabetic (e.g Vigenère cipher).

It can be useful for detecting the type of cipher and estimating the encryption key length (width).

For the application of this see:

https://en.wikipedia.org/wiki/Index_of_coincidence#Application

Development Installation​

To install azul-plugin-index-coincidence for development run the command (from the root directory of this project):

pip install -e .

Usage​

Usage on local files:

$ azul-index-coincidence test_039.enc
Output features:
    index_of_coincidence_width: 0.10374224863997697 - 39
        index_of_coincidence: 0.0039474089988589525

The 'index_of_coincidence' feature is the result of the file as it is. The 'index_of_coincidence_width' feature shows that the index of coincidence increases significantly (from 0.0039 -> 0.1037) with a width of 39.

Check azul-plugin-index-coincidence --help for advanced usage.

Python Package management​

This python package is managed using a setup.py and pyproject.toml file.

Standardisation of installing and testing the python package is handled through tox. Tox commands include:

# Run all standard tox actions
tox
# Run linting only
tox -e style
# Run tests only
tox -e test

Dependency management​

Dependencies are managed in the requirements.txt, requirements_test.txt and debian.txt file.

The requirements files are the python package dependencies for normal use and specific ones for tests (e.g pytest, black, flake8 are test only dependencies).

The debian.txt file manages the debian dependencies that need to be installed on development systems and docker images.

Sometimes the debian.txt file is insufficient and in this case the Dockerfile may need to be modified directly to install complex dependencies.