v3.0.0: Add password-based encryption, BMP support, version flag

[Copilot]

The tool lacked encryption—hidden messages could be extracted by anyone. This release adds the most critical missing capability for a security-oriented steganography toolkit.

Encryption (stegano/crypto.py)

• Password-based authenticated encryption using Fernet (AES-128-CBC + HMAC-SHA256, PBKDF2 600K iterations)
• encrypt_message(), decrypt_message(), is_encrypted() exported from package
• Encrypted messages prefixed with STEGENC1: for auto-detection during decode
• Backwards compatible: unencrypted messages decode as before

CLI

• -p/--password flag on encode and decode subcommands
• -V/--version flag
• Auto-detects encrypted messages and prompts for password if missing

# Encode with encryption
python stegano_sec.py encode -i input.png -o output.png -m "Secret" -p mypass

# Decode — detects encryption automatically
python stegano_sec.py decode -i output.png -p mypass

GUI

• Password entry fields added to Encode and Decode tabs
• Auto-detection of encrypted messages with user prompts

BMP Support

• Added .bmp to valid image formats in utils.py, CLI, and GUI file dialogs

Dependencies

• Added cryptography>=42.0.4 (no known advisories on 42.0.4+)

Tests

• 6 new tests: encrypt/decrypt cycle, wrong password, passthrough, detection, end-to-end encrypted steganography, BMP format validation
• 11 total, all passing

---

💡 You can make Copilot smarter by setting up custom instructions, customizing its development environment and configuring Model Context Protocol (MCP) servers. Learn more Copilot coding agent tips in the docs.