ChronoFidelius 1.0.2

A Python library for for plaintext encryption using homophonic substitution and historical character frequencies.

ChronoFidelius

ChronoFidelius is a Python library for plaintext encryption using homophonic substitution and historical character frequencies. It provides configurable error injection, frequency-based key generation, and advanced encryption techniques inspired by historical cryptography.

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Features

• Homophonic Substitution Cipher: Encrypts plaintext with multiple cipher options for each character
• Frequency-Based Key Generation: Supports even and uneven key generation using historical unigram frequencies
• Error Injection: Introduces errors (additions, deletions, or doubles) into plaintext for obfuscation
• Custom Configurations: Control error frequency, character spacing, and more

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Installation

Install ChronoFidelius using pip:

pip install ChronoFidelius

Or, install directly from the source:

git clone https://github.com/mbruton0426/ChronoFidelius.git
cd ChronoFidelius
pip install .

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Usage

When initializing ChronoFidelius, the only required variable is some text to encrypt, either as a str or list of str.

Initalization:

from chronofidelius import ChronoFidelius

# Initialize the ChronoFidelius object
cf = ChronoFidelius("Hello, World!")

Optional Parameters: initialization

• set_seed (int, optional): A seed value for reproducibility of random operations. Default is None
• include_errors (bool, optional): If True, introduces errors (e.g., additions, deletions, doubles) into the plaintext. Default is False
• error_type (str, optional): Specifies the type of error to introduce. Must be set if include_errors is True. Default is None. Valid options are: - "additions": Adds random characters - "deletions": Removes characters - "doubles": Doubles characters - "all": Randomly selects between "additions", "deletions", or "doubles"
• error_frequency (float, optional): Frequency of errors in the plaintext (0–1). For example, 0.05 introduces errors to 5% of the text. Default is 0.05
• include_spacing (bool, optional): If True, retains spaces and line breaks during formatting. Default is False
• max_length (int, optional): Maximum length of the formatted plaintext or chunks. Default is 200
• set_punctuation (str, optional): Specifies the set of punctuation characters to remove. Default is string.punctuation

Encrypting Plaintexts

Plaintexts can be encrypted with:

cf.encrypt_homophonic()

This automatically encrypts plaintext(s) according to every possible option based on the default values. Plaintext(s), ciphertexts, and keys are then all available as a dictionary in:

cf.pt_ct_dict

Optional Parameters: encrypt_homophonic()

• key_type (str): The type of encryption key ("even", "uneven", or "both"). Default is "even"
• lang_code (str): Language code for character frequencies. Options: {'en', 'es', 'sv', 'de', 'fr', 'it'}
• freq_year (str): Year range for character frequencies. Varies by language, available in chronofidelius/unigram_frequencies.py
• set_frequencies (dict): Custom frequency mappings for uneven key generation
• set_alphabet (str): Alphabet to use for key generation

Utilizing Custom Character Frequencies

All uneven-type encryptions require character frequencies. If the frequencies you would like to use are not available in chronofidelius/unigram_frequencies.py, you may input your own.

# Custom frequency dictionary
custom_frequencies = {"A": 0.1, "B": 0.2, "C": 0.3, "D": 0.4}

cf.encrypt_homophonic(set_frequencies=custom_frequencies)

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License

This project is licensed under the Apache License 2.0. See the LICENSE file for details.

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Citation

If you use this tool in your research, please cite:

@inproceedings{bruton2025statistics,
  title     = {From Statistics to Neural Networks: Enhancing Ciphertext-Plaintext Alignment in Historical Substitution Ciphers For Automatic Key Extraction},
  author    = {Bruton, Micaella and Megyesi, Be{\'a}ta},
  booktitle = {Proceedings of the International Conference on Historical Cryptology (HistoCrypt)},
  year      = {2025},
}