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This project is a Python command-line implementation of the affine cipher, a classical substitution cipher where each letter is transformed by `E(x) = (ax + b) mod 26` and reversed using the modular multiplicative inverse of `a`. It's built with `uv`, has a full test suite, and carries a thorough linting, type-checking, and security-scanning toolchain enforced through pre-commit hooks and GitHub Actions CI.

The CLI encrypts and decrypts text through `encrypt`/`decrypt` subcommands. Encryption requires an explicit key, validated to ensure it's mathematically accurate before it's used, so a bad key fails loudly instead of silently breaking the cipher. Decryption works either with a known key or by brute-forcing every valid key when the key isn't known. Both directions preserve each letter's original case and leave punctuation and spacing untouched.

A command-line tool that encrypts and decrypts text using the affine cipher, with case preservation and both known-key and brute-force decryption.

projects tag: github-actions-ci

Affine Cipher CLI