Add CI/CD workflows and security policy

.github/CI_CD_PRIMER.md

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+# CI/CD Primer for Stegasoo
+
+## What is CI/CD?
+
+**CI** = Continuous Integration
+**CD** = Continuous Deployment
+
+Think of it as a robot assistant that automatically:
+1. **Tests your code** every time you push
+2. **Checks formatting** so code stays consistent
+3. **Publishes releases** when you tag a version
+
+```
+You push code → GitHub runs workflows → You get ✓ or ✗
+```
+
+---
+
+## How It Works
+
+### The Trigger
+
+When you `git push` or create a Pull Request, GitHub looks for workflow files in:
+```
+.github/workflows/*.yml
+```
+
+Each `.yml` file defines a workflow - a series of steps to run.
+
+### The Runners
+
+GitHub provides free Linux/Mac/Windows VMs that:
+1. Clone your repo
+2. Set up Python
+3. Run your commands
+4. Report success/failure
+
+You don't manage servers - GitHub does.
+
+---
+
+## Your Workflows
+
+### 1. `test.yml` - Run Tests on Every Push
+
+**When it runs:** Every push, every PR
+
+**What it does:**
+```
+1. Spins up Ubuntu VM
+2. Installs Python 3.10, 3.11, 3.12
+3. Installs your package + dependencies
+4. Runs pytest
+5. Reports pass/fail
+```
+
+**You'll see:** Green ✓ or red ✗ on your commits
+
+### 2. `lint.yml` - Check Code Style
+
+**When it runs:** Every push, every PR
+
+**What it does:**
+```
+1. Runs ruff (fast Python linter)
+2. Checks black formatting
+3. Fails if code isn't formatted
+```
+
+**Why:** Keeps code consistent, catches common bugs
+
+### 3. `release.yml` - Publish to PyPI
+
+**When it runs:** Only when you create a version tag
+
+**What it does:**
+```
+1. Builds the package (wheel + sdist)
+2. Uploads to PyPI
+```
+
+**You trigger it by:**
+```bash
+git tag v2.2.0
+git push origin v2.2.0
+```
+
+---
+
+## Day-to-Day Usage
+
+### Normal Development
+
+```bash
+# Make changes
+git add .
+git commit -m "Add new feature"
+git push
+```
+
+Then check GitHub → Actions tab → See if tests pass.
+
+### If Tests Fail
+
+1. Click the failed workflow
+2. Click the failed job
+3. Read the error log
+4. Fix locally, push again
+
+### Making a Release
+
+```bash
+# 1. Update version in pyproject.toml and constants.py
+# 2. Commit the version bump
+git add .
+git commit -m "Bump version to 2.2.1"
+git push
+
+# 3. Create and push a tag
+git tag v2.2.1
+git push origin v2.2.1
+
+# 4. GitHub automatically publishes to PyPI
+```
+
+---
+
+## Reading the GitHub UI
+
+### Actions Tab
+
+```
+Repository → Actions → [List of workflow runs]
+```
+
+Each run shows:
+- ✓ Green checkmark = passed
+- ✗ Red X = failed
+- 🟡 Yellow dot = running
+
+### Pull Request Checks
+
+When you open a PR, you'll see:
+```
+┌─────────────────────────────────────────┐
+│ All checks have passed                  │
+│ ✓ test (3.10) — 45s                     │
+│ ✓ test (3.11) — 42s                     │
+│ ✓ test (3.12) — 44s                     │
+│ ✓ lint — 12s                            │
+└─────────────────────────────────────────┘
+```
+
+---
+
+## Setting Up PyPI Publishing
+
+For `release.yml` to work, you need to add a PyPI API token:
+
+### One-Time Setup
+
+1. **Create PyPI account** at https://pypi.org/account/register/
+
+2. **Generate API token:**
+   - PyPI → Account Settings → API tokens
+   - Create token (scope: entire account or just stegasoo)
+   - Copy the token (starts with `pypi-`)
+
+3. **Add to GitHub:**
+   - GitHub repo → Settings → Secrets and variables → Actions
+   - New repository secret
+   - Name: `PYPI_API_TOKEN`
+   - Value: paste the token
+
+Now `release.yml` can publish automatically.
+
+---
+
+## Common Scenarios
+
+### "Tests pass locally but fail in CI"
+
+Usually means:
+- Missing dependency in `pyproject.toml`
+- Hardcoded path that doesn't exist in CI
+- Test relies on local file
+
+### "Lint is failing"
+
+Run locally to see/fix:
+```bash
+# Check issues
+ruff check src/
+
+# Auto-fix what's possible
+ruff check --fix src/
+
+# Format code
+black src/
+```
+
+### "I want to skip CI for a commit"
+
+Add `[skip ci]` to commit message:
+```bash
+git commit -m "Update README [skip ci]"
+```
+
+---
+
+## Costs
+
+GitHub Actions is **free** for public repos.
+
+For private repos: 2,000 minutes/month free, then paid.
+
+---
+
+## Summary
+
+| Action | What Happens |
+|--------|--------------|
+| `git push` | Tests + lint run automatically |
+| Open PR | Tests must pass before merge |
+| `git tag v*` | Publishes to PyPI |
+| Check results | GitHub → Actions tab |
+
+That's it! Push code, check for green checkmarks.

.github/workflows/lint.yml

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+# Check code style and formatting
+name: Lint
+
+on:
+  push:
+    branches: [main, master, develop]
+  pull_request:
+    branches: [main, master, develop]
+
+jobs:
+  lint:
+    runs-on: ubuntu-latest
+    
+    steps:
+      # 1. Get the code
+      - name: Checkout code
+        uses: actions/checkout@v4
+      
+      # 2. Set up Python
+      - name: Set up Python
+        uses: actions/setup-python@v5
+        with:
+          python-version: "3.11"
+      
+      # 3. Install linting tools
+      - name: Install linters
+        run: |
+          python -m pip install --upgrade pip
+          pip install ruff black
+      
+      # 4. Run ruff (fast linter - catches bugs and style issues)
+      - name: Run ruff
+        run: |
+          ruff check src/ tests/ frontends/
+      
+      # 5. Check black formatting (doesn't modify, just checks)
+      - name: Check black formatting
+        run: |
+          black --check src/ tests/ frontends/
+
+  # Type checking (optional but helpful)
+  typecheck:
+    runs-on: ubuntu-latest
+    
+    steps:
+      - name: Checkout code
+        uses: actions/checkout@v4
+      
+      - name: Set up Python
+        uses: actions/setup-python@v5
+        with:
+          python-version: "3.11"
+      
+      - name: Install dependencies
+        run: |
+          python -m pip install --upgrade pip
+          pip install -e ".[dev]"
+          pip install mypy
+      
+      - name: Run mypy
+        run: |
+          mypy src/stegasoo --ignore-missing-imports
+        continue-on-error: true  # Don't fail build on type errors (yet)

.github/workflows/release.yml

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+# Publish to PyPI when a version tag is pushed
+name: Release
+
+on:
+  push:
+    tags:
+      - 'v*'  # Triggers on v1.0.0, v2.1.0, etc.
+
+jobs:
+  # First, run tests to make sure everything works
+  test:
+    runs-on: ubuntu-latest
+    
+    steps:
+      - name: Checkout code
+        uses: actions/checkout@v4
+      
+      - name: Set up Python
+        uses: actions/setup-python@v5
+        with:
+          python-version: "3.11"
+      
+      - name: Install system dependencies
+        run: |
+          sudo apt-get update
+          sudo apt-get install -y libzbar0
+      
+      - name: Install package
+        run: |
+          python -m pip install --upgrade pip
+          pip install -e ".[dev]"
+      
+      - name: Run tests
+        run: pytest
+
+  # Then build and publish
+  publish:
+    needs: test  # Only run if tests pass
+    runs-on: ubuntu-latest
+    
+    # Required for PyPI trusted publishing (recommended)
+    permissions:
+      id-token: write
+    
+    steps:
+      - name: Checkout code
+        uses: actions/checkout@v4
+      
+      - name: Set up Python
+        uses: actions/setup-python@v5
+        with:
+          python-version: "3.11"
+      
+      - name: Install build tools
+        run: |
+          python -m pip install --upgrade pip
+          pip install build twine
+      
+      - name: Build package
+        run: python -m build
+      
+      - name: Check package
+        run: twine check dist/*
+      
+      # Option 1: Trusted Publishing (recommended, no token needed)
+      # Set this up at: https://pypi.org/manage/project/stegasoo/settings/publishing/
+      - name: Publish to PyPI (Trusted Publishing)
+        uses: pypa/gh-action-pypi-publish@release/v1
+        # No token needed if you configure trusted publishing on PyPI
+      
+      # Option 2: API Token (uncomment if not using trusted publishing)
+      # - name: Publish to PyPI (API Token)
+      #   env:
+      #     TWINE_USERNAME: __token__
+      #     TWINE_PASSWORD: ${{ secrets.PYPI_API_TOKEN }}
+      #   run: twine upload dist/*
+
+  # Create GitHub Release with changelog
+  github-release:
+    needs: publish
+    runs-on: ubuntu-latest
+    
+    permissions:
+      contents: write  # Needed to create releases
+    
+    steps:
+      - name: Checkout code
+        uses: actions/checkout@v4
+      
+      - name: Create GitHub Release
+        uses: softprops/action-gh-release@v1
+        with:
+          generate_release_notes: true
+          files: |
+            dist/*

.github/workflows/test.yml

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+# Run tests on every push and pull request
+name: Tests
+
+on:
+  push:
+    branches: [main, master, develop]
+  pull_request:
+    branches: [main, master, develop]
+
+jobs:
+  test:
+    runs-on: ubuntu-latest
+    
+    strategy:
+      fail-fast: false  # Don't cancel other jobs if one fails
+      matrix:
+        python-version: ["3.10", "3.11", "3.12"]
+    
+    steps:
+      # 1. Get the code
+      - name: Checkout code
+        uses: actions/checkout@v4
+      
+      # 2. Set up Python
+      - name: Set up Python ${{ matrix.python-version }}
+        uses: actions/setup-python@v5
+        with:
+          python-version: ${{ matrix.python-version }}
+      
+      # 3. Install system dependencies (for pyzbar QR reading)
+      - name: Install system dependencies
+        run: |
+          sudo apt-get update
+          sudo apt-get install -y libzbar0
+      
+      # 4. Install the package with all dependencies
+      - name: Install package
+        run: |
+          python -m pip install --upgrade pip
+          pip install -e ".[dev]"
+      
+      # 5. Run tests with coverage
+      - name: Run tests
+        run: |
+          pytest --cov=stegasoo --cov-report=xml --cov-report=term-missing
+      
+      # 6. Upload coverage report (optional - integrates with codecov.io)
+      - name: Upload coverage
+        uses: codecov/codecov-action@v4
+        if: matrix.python-version == '3.11'  # Only upload once
+        with:
+          files: ./coverage.xml
+          fail_ci_if_error: false  # Don't fail if codecov is down

.pre-commit-config.yaml

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+# Pre-commit hooks - run formatting/linting before each commit
+# Install: pip install pre-commit && pre-commit install
+# Manual run: pre-commit run --all-files
+
+repos:
+  # Ruff - fast Python linter (replaces flake8, isort, etc.)
+  - repo: https://github.com/astral-sh/ruff-pre-commit
+    rev: v0.1.6
+    hooks:
+      - id: ruff
+        args: [--fix]  # Auto-fix what's possible
+      - id: ruff-format  # Ruff's formatter (alternative to black)
+
+  # Black - code formatter (comment out if using ruff-format above)
+  # - repo: https://github.com/psf/black
+  #   rev: 23.11.0
+  #   hooks:
+  #     - id: black
+
+  # Basic file hygiene
+  - repo: https://github.com/pre-commit/pre-commit-hooks
+    rev: v4.5.0
+    hooks:
+      - id: trailing-whitespace      # Remove trailing spaces
+      - id: end-of-file-fixer        # Ensure newline at EOF
+      - id: check-yaml               # Validate YAML
+      - id: check-toml               # Validate TOML
+      - id: check-added-large-files  # Prevent giant files
+        args: ['--maxkb=1000']
+      - id: check-merge-conflict     # No merge conflict markers
+      - id: debug-statements         # No print() or pdb left behind
+
+  # Security checks
+  - repo: https://github.com/PyCQA/bandit
+    rev: 1.7.6
+    hooks:
+      - id: bandit
+        args: ["-c", "pyproject.toml"]
+        additional_dependencies: ["bandit[toml]"]
+        exclude: tests/

SECURITY.md

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+# Security Policy
+
+## Supported Versions
+
+| Version | Supported          |
+| ------- | ------------------ |
+| 2.x.x   | :white_check_mark: |
+| 1.x.x   | :x:                |
+
+## Reporting a Vulnerability
+
+**Please do not report security vulnerabilities through public GitHub issues.**
+
+Instead, please email: **security@example.com** (replace with your email)
+
+Include:
+- Description of the vulnerability
+- Steps to reproduce
+- Potential impact
+- Any suggested fixes
+
+You should receive a response within 48 hours. We'll work with you to understand and address the issue.
+
+---
+
+# Threat Model
+
+## What Stegasoo Protects
+
+Stegasoo is designed to hide the **existence** of a secret message within an ordinary-looking image, protected by multi-factor authentication.
+
+### Protection Goals
+
+| Goal | How It's Achieved |
+|------|-------------------|
+| **Confidentiality** | AES-256-GCM encryption with Argon2id key derivation |
+| **Steganography** | LSB embedding with pseudo-random pixel selection |
+| **Authentication** | Multi-factor: reference photo + passphrase + PIN (or RSA key) |
+| **Integrity** | GCM authentication tag detects tampering |
+
+### Security Factors
+
+Stegasoo combines multiple authentication factors:
+
+```
+┌─────────────────────────────────────────────────────────────┐
+│                     Key Derivation                          │
+│                                                             │
+│  Reference Photo ─────┐                                     │
+│  (something you have) │                                     │
+│                       ├──► Argon2id ──► AES-256 Key         │
+│  Day Passphrase ──────┤    (256MB RAM)                      │
+│  (something you know) │                                     │
+│                       │                                     │
+│  PIN or RSA Key ──────┘                                     │
+│  (second factor)                                            │
+└─────────────────────────────────────────────────────────────┘
+```
+
+## What Stegasoo Does NOT Protect Against
+
+### 1. Statistical Steganalysis
+
+**Risk:** Advanced analysis can detect that an image contains hidden data.
+
+**Reality:** LSB steganography is detectable by:
+- Chi-square analysis
+- RS analysis
+- Machine learning classifiers
+
+**Mitigation:** Stegasoo uses pseudo-random pixel selection (not sequential), which helps but doesn't eliminate detectability.
+
+**Recommendation:** Don't rely on Stegasoo if your adversary has:
+- Access to the original carrier image
+- Sophisticated forensic tools
+- Motivation to analyze your specific images
+
+### 2. Compromised Endpoints
+
+**Risk:** If your device is compromised, the attacker can capture credentials.
+
+**Not protected:**
+- Keyloggers capturing your PIN/passphrase
+- Screen capture of decoded messages
+- Memory scraping during encode/decode
+- Malware on sender or receiver device
+
+**Recommendation:** Use on trusted devices only.
+
+### 3. Reference Photo Exposure
+
+**Risk:** The reference photo is a critical secret.
+
+**If leaked:** Attacker only needs to guess/brute-force the passphrase + PIN.
+
+**Recommendation:**
+- Never share the reference photo
+- Use a unique photo (not posted online)
+- Store securely (encrypted drive, password manager)
+
+### 4. Weak Credentials
+
+**Risk:** Short PINs or common passphrases can be brute-forced.
+
+| PIN Length | Combinations | Time to Brute Force* |
+|------------|--------------|----------------------|
+| 4 digits   | 10,000       | Seconds              |
+| 6 digits   | 1,000,000    | Minutes              |
+| 8 digits   | 100,000,000  | Hours                |
+| 9 digits   | 1,000,000,000| Days                 |
+
+*With Argon2 (256MB RAM, 4 iterations), each attempt takes ~1 second, making brute force slow but not impossible for short PINs.
+
+**Recommendation:**
+- Use 8+ digit PINs
+- Use 4+ word passphrases
+- Consider RSA keys for high-security use cases
+
+### 5. Image Modification
+
+**Risk:** Lossy compression destroys hidden data.
+
+**Data is destroyed by:**
+- JPEG compression
+- Resizing
+- Filters/effects
+- Screenshots
+- Social media upload (Instagram, Twitter, etc.)
+
+**Recommendation:** 
+- Always use lossless formats (PNG, BMP)
+- Transfer files directly (email, Signal, USB)
+- Never upload stego images to social media
+
+### 6. Metadata Leakage
+
+**Risk:** The stego image itself may reveal information.
+
+**Potential leaks:**
+- File creation timestamp
+- Camera EXIF data (if carrier has it)
+- File size changes
+
+**Mitigation:** Stegasoo strips EXIF on output, but timestamps remain.
+
+### 7. Traffic Analysis
+
+**Risk:** The act of sending an image may be suspicious.
+
+**Not protected:**
+- Network observers seeing you send image files
+- Email metadata showing sender/receiver
+- Frequency analysis of communications
+
+**Recommendation:** Use alongside normal image-sharing behavior.
+
+## Cryptographic Details
+
+### Encryption
+
+| Component | Algorithm | Parameters |
+|-----------|-----------|------------|
+| Key Derivation | Argon2id | 256MB RAM, 4 iterations, 4 parallelism |
+| Fallback KDF | PBKDF2-SHA256 | 600,000 iterations |
+| Encryption | AES-256-GCM | 12-byte IV, 16-byte tag |
+| Photo Hash | SHA-256 | Full image bytes |
+
+### Pixel Selection
+
+Pixels are selected pseudo-randomly using a key derived from:
+```
+pixel_key = SHA256(photo_hash || passphrase || date || pin/rsa_signature)
+```
+
+This prevents:
+- Sequential embedding patterns
+- Statistical detection of modified regions
+
+### Format
+
+```
+┌──────────────────────────────────────────────────────────────┐
+│ Magic (4B) │ Version (1B) │ Date (10B) │ Salt (32B) │ IV (12B) │
+├──────────────────────────────────────────────────────────────┤
+│ Encrypted Payload (AES-256-GCM)                              │
+│ ├── Type (1B): 0x01=text, 0x02=file                          │
+│ ├── Length (4B)                                              │
+│ ├── Data (variable)                                          │
+│ └── [Filename if file] (variable)                            │
+├──────────────────────────────────────────────────────────────┤
+│ GCM Auth Tag (16B)                                           │
+└──────────────────────────────────────────────────────────────┘
+```
+
+## Best Practices
+
+### For Maximum Security
+
+1. **Use RSA keys** instead of PINs for authentication
+2. **Use unique reference photos** not available online
+3. **Use long passphrases** (4+ random words)
+4. **Transfer via secure channels** (Signal, encrypted email)
+5. **Delete stego images** after message is read
+6. **Keep software updated** for security fixes
+
+### For Casual Privacy
+
+1. **6-digit PIN** is sufficient for non-adversarial use
+2. **3-word passphrase** provides reasonable security
+3. **PNG format** always for output
+4. **Direct file transfer** (email attachment, AirDrop)
+
+## Known Limitations
+
+| Limitation | Impact | Status |
+|------------|--------|--------|
+| LSB is detectable | Statistical analysis can detect hidden data | By design (tradeoff for capacity) |
+| No forward secrecy | Compromised key decrypts all messages | Use different keys per message for high security |
+| Date in header | Reveals when message was encoded | By design (enables day-specific passphrases) |
+| No deniability | Single password = single message | Future: plausible deniability layers |
+
+## Security Audit Status
+
+This software has **not** been professionally audited. Use at your own risk for sensitive applications.
+
+If you're a security researcher interested in auditing Stegasoo, please reach out.
+
+---
+
+## Version History (Security Relevant)
+
+| Version | Security Changes |
+|---------|------------------|
+| 2.2.0   | Added compression (no security impact) |
+| 2.1.0   | Upgraded to Argon2id, increased iterations |
+| 2.0.0   | Added RSA key support |
+| 1.0.0   | Initial release |