Add audio steganography with LSB and spread spectrum modes
Implement two audio embedding modes following the same multi-factor
authentication pipeline as image steganography (passphrase + PIN +
optional RSA key + optional channel key):
- audio_lsb: High-capacity LSB embedding in PCM samples for lossless
formats (WAV/FLAC). Uses ChaCha20-keyed sample index selection.
- audio_spread: Direct-sequence spread spectrum (DSSS) with ChaCha20-
keyed bipolar chip codes, Reed-Solomon error correction, and 3-copy
majority-voted length headers. Designed to survive lossy compression.
New files:
- audio_steganography.py: LSB embed/extract on PCM samples
- spread_steganography.py: Spread spectrum embed/extract
- audio_utils.py: Format detection, transcoding, validation helpers
- tests/test_audio.py: 22 tests covering both modes end-to-end
Updated encode.py, decode.py, cli.py (audio-encode/audio-decode
commands), constants.py, models.py, exceptions.py, validation.py,
__init__.py, and pyproject.toml ([audio] extra).
Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>
0248bec813