GcmCrypt-Python

Python port of GcmCrypt (.NET).
Implements the same AES-GCM file format, header structure, and chunking rules as documented in the .NET repo.

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Features

• Encrypt/decrypt files with AES-256 GCM
• Intended file-format compatibility with the .NET version (header, chunking, 16-byte tags)
• Cross-platform (Windows, Linux, macOS)
• Console messages aligned with .NET where practical (e.g., clearer GCM auth-tag failures)

Requirements

• Python 3.6+
  Note: Python 3.6 is end-of-life; newer Python versions are recommended for security and support.
• cryptography (preferred)

pip install cryptography

• Optional fallback: pycryptodome

Usage

# Encrypt
python gcmcrypt.py -e password input.txt output.gcm

# Decrypt
python gcmcrypt.py -d password input.gcm output.txt

Interop

• The goal is for files encrypted with this script to decrypt with the .NET GcmCrypt, and vice versa.
• Follow the .NET repo’s “Encrypted File Format” and “AES GCM Mode Technical Notes” for parity.

Notes

If a decryption fails due to an authentication error and the underlying library error is empty, the script should print:

Decryption failed: likely wrong password or corrupted file

License

MIT — same as the .NET project.