{% extends "base.html" %}

{% block title %}About - Stego{% endblock %}

{% block content %}
<div class="row justify-content-center">
    <div class="col-lg-10">
        <div class="card mb-4">
            <div class="card-header">
                <h5 class="mb-0"><i class="bi bi-info-circle me-2"></i>About Stego</h5>
            </div>
            <div class="card-body">
                <p class="lead">
                    Stego hides encrypted messages and files inside images using multi-factor authentication.
                </p>
                
                <h6 class="text-primary mt-4 mb-3">Features</h6>
                <div class="row">
                    <div class="col-md-6">
                        <ul class="list-unstyled">
                            <li class="mb-2">
                                <i class="bi bi-check-circle text-success me-2"></i>
                                <strong>Text &amp; File Embedding</strong>
                                <br><small class="text-muted">Any file type: PDF, ZIP, documents</small>
                            </li>
                            <li class="mb-2">
                                <i class="bi bi-check-circle text-success me-2"></i>
                                <strong>Multi-Factor Security</strong>
                                <br><small class="text-muted">Photo + passphrase + PIN/RSA key</small>
                            </li>
                            <li class="mb-2">
                                <i class="bi bi-check-circle text-success me-2"></i>
                                <strong>AES-256-GCM Encryption</strong>
                                <br><small class="text-muted">Authenticated encryption with integrity check</small>
                            </li>
                            <li class="mb-2">
                                <i class="bi bi-check-circle text-success me-2"></i>
                                <strong>DCT &amp; LSB Modes</strong>
                                <br><small class="text-muted">JPEG resilience (DCT) or high capacity (LSB)</small>
                            </li>
                        </ul>
                    </div>
                    <div class="col-md-6">
                        <ul class="list-unstyled">
                            <li class="mb-2">
                                <i class="bi bi-check-circle text-success me-2"></i>
                                <strong>Random Pixel Embedding</strong>
                                <br><small class="text-muted">Defeats statistical analysis</small>
                            </li>
                            <li class="mb-2">
                                <i class="bi bi-check-circle text-success me-2"></i>
                                <strong>Large Image Support</strong>
                                <br><small class="text-muted">Up to {{ max_payload_kb }} KB, tested with 14MB+ images</small>
                            </li>
                            <li class="mb-2">
                                <i class="bi bi-check-circle text-success me-2"></i>
                                <strong>Zero Server Storage</strong>
                                <br><small class="text-muted">Nothing saved, files auto-expire</small>
                            </li>
                            <li class="mb-2">
                                <i class="bi bi-check-circle text-success me-2"></i>
                                <strong>QR Code Keys</strong>
                                <br><small class="text-muted">Import/export RSA keys via QR</small>
                            </li>
                            <li class="mb-2">
                                <i class="bi bi-check-circle text-success me-2"></i>
                                <strong>Channel Keys</strong>
                                <span class="badge bg-info ms-1">v4.1</span>
                                <br><small class="text-muted">Group/deployment isolation</small>
                            </li>
                        </ul>
                    </div>
                </div>
            </div>
        </div>
        
        <!-- Embedding Modes -->
        <div class="card mb-4">
            <div class="card-header">
                <h5 class="mb-0"><i class="bi bi-cpu me-2"></i>Embedding Modes</h5>
            </div>
            <div class="card-body">
                <p>Two modes optimized for different use cases.</p>
                
                <div class="row mt-4">
                    <!-- DCT Mode -->
                    <div class="col-md-6 mb-4">
                        <div class="card bg-dark h-100">
                            <div class="card-header">
                                <i class="bi bi-soundwave text-warning me-2"></i>
                                <strong>DCT Mode</strong>
                                <span class="badge bg-success ms-2">Default</span>
                            </div>
                            <div class="card-body">
                                <p class="small">
                                    <strong>DCT (Discrete Cosine Transform)</strong> embeds data in frequency coefficients. Survives JPEG recompression.
                                </p>
                                <ul class="small mb-0">
                                    <li><strong>Capacity:</strong> ~75 KB/MP</li>
                                    <li><strong>Output:</strong> JPEG or PNG</li>
                                    <li><strong>Color:</strong> Color or grayscale</li>
                                    <li><strong>Speed:</strong> ~2s</li>
                                    <li><strong>Error Correction:</strong> Reed-Solomon</li>
                                </ul>
                                <hr>
                                <div class="small">
                                    <i class="bi bi-check-circle text-success me-1"></i> Instagram, Facebook<br>
                                    <i class="bi bi-check-circle text-success me-1"></i> WhatsApp, Signal, Telegram<br>
                                    <i class="bi bi-check-circle text-success me-1"></i> Twitter/X<br>
                                    <i class="bi bi-check-circle text-success me-1"></i> Any recompressing platform
                                </div>
                            </div>
                        </div>
                    </div>
                    
                    <!-- LSB Mode -->
                    <div class="col-md-6 mb-4">
                        <div class="card bg-dark h-100">
                            <div class="card-header">
                                <i class="bi bi-grid-3x3-gap text-primary me-2"></i>
                                <strong>LSB Mode</strong>
                            </div>
                            <div class="card-body">
                                <p class="small">
                                    <strong>LSB (Least Significant Bit)</strong> embeds data in the lowest bit of each color channel. Imperceptible to the eye.
                                </p>
                                <ul class="small mb-0">
                                    <li><strong>Capacity:</strong> ~375 KB/MP</li>
                                    <li><strong>Output:</strong> PNG (lossless)</li>
                                    <li><strong>Color:</strong> Full color</li>
                                    <li><strong>Speed:</strong> ~0.5s</li>
                                </ul>
                                <hr>
                                <div class="small">
                                    <i class="bi bi-check-circle text-success me-1"></i> Email attachments<br>
                                    <i class="bi bi-check-circle text-success me-1"></i> Cloud storage<br>
                                    <i class="bi bi-check-circle text-success me-1"></i> Direct file transfer<br>
                                    <i class="bi bi-x-circle text-danger me-1"></i> Social media
                                </div>
                            </div>
                        </div>
                    </div>
                </div>
                
                <!-- Mode Comparison Table -->
                <h6 class="mt-3"><i class="bi bi-table me-2"></i>Comparison</h6>
                <div class="table-responsive">
                    <table class="table table-dark table-sm small">
                        <thead>
                            <tr>
                                <th>Aspect</th>
                                <th>DCT Mode <span class="badge bg-success ms-1">Default</span></th>
                                <th>LSB Mode</th>
                            </tr>
                        </thead>
                        <tbody>
                            <tr>
                                <td>Capacity (1080p)</td>
                                <td class="text-warning">~50 KB</td>
                                <td class="text-success">~770 KB</td>
                            </tr>
                            <tr>
                                <td>Survives JPEG</td>
                                <td class="text-success">✅ Yes</td>
                                <td class="text-danger">❌ No</td>
                            </tr>
                            <tr>
                                <td>Social Media</td>
                                <td class="text-success">✅ Works</td>
                                <td class="text-danger">❌ Broken</td>
                            </tr>
                            <tr>
                                <td>Detection Resistance</td>
                                <td>Better</td>
                                <td>Moderate</td>
                            </tr>
                        </tbody>
                    </table>
                </div>
                
                <div class="alert alert-info small mt-3 mb-0">
                    <i class="bi bi-lightbulb me-2"></i>
                    <strong>Auto-Detection:</strong> Mode is detected automatically when decoding.
                </div>
            </div>
        </div>
        
        <div class="card mb-4">
            <div class="card-header">
                <h5 class="mb-0"><i class="bi bi-shield-lock me-2"></i>How Security Works</h5>
            </div>
            <div class="card-body">
                <p>Multi-factor authentication derives encryption keys:</p>
                
                <div class="row text-center my-4">
                    <div class="col-6 col-lg-3 mb-3">
                        <div class="p-3 bg-dark rounded h-100 d-flex flex-column align-items-center">
                            <i class="bi bi-image text-info fs-2 d-block mb-2"></i>
                            <strong>Reference Photo</strong>
                            <div class="small text-muted mt-1">Something you have</div>
                            <div class="small text-success mt-auto pt-2">~80-256 bits</div>
                        </div>
                    </div>
                    <div class="col-6 col-lg-3 mb-3">
                        <div class="p-3 bg-dark rounded h-100 d-flex flex-column align-items-center">
                            <i class="bi bi-chat-quote text-warning fs-2 d-block mb-2"></i>
                            <strong>Passphrase</strong>
                            <div class="small text-muted mt-1">Something you know</div>
                            <div class="small text-success mt-auto pt-2">~44 bits (4 words)</div>
                        </div>
                    </div>
                    <div class="col-6 col-lg-3 mb-3">
                        <div class="p-3 bg-dark rounded h-100 d-flex flex-column align-items-center">
                            <i class="bi bi-123 text-danger fs-2 d-block mb-2"></i>
                            <strong>Static PIN</strong>
                            <div class="small text-muted mt-1">Something you know</div>
                            <div class="small text-success mt-auto pt-2">~20 bits (6 digits)</div>
                        </div>
                    </div>
                    <div class="col-6 col-lg-3 mb-3">
                        <div class="p-3 bg-dark rounded h-100 d-flex flex-column align-items-center">
                            <i class="bi bi-key text-primary fs-2 d-block mb-2"></i>
                            <strong>RSA Key</strong>
                            <div class="small text-muted mt-1">Optional</div>
                            <div class="small text-success mt-auto pt-2">~128 bits</div>
                        </div>
                    </div>
                </div>
                
                <div class="alert alert-secondary">
                    <i class="bi bi-calculator me-2"></i>
                    <strong>Combined entropy:</strong> 144-424+ bits. 128 bits is infeasible to brute force.
                </div>
                
                <h6 class="mt-4">Key Derivation</h6>
                <p>
                    {% if has_argon2 %}
                    <span class="badge bg-success me-1"><i class="bi bi-check"></i> Argon2id</span>
                    256MB memory cost. Memory-hard KDF defeats GPU/ASIC attacks.
                    {% else %}
                    <span class="badge bg-warning text-dark me-1"><i class="bi bi-exclamation-triangle"></i> Argon2 Not Available</span>
                    Using PBKDF2-SHA512 with 600k iterations.
                    Install <code>argon2-cffi</code> for stronger security.
                    {% endif %}
                </p>
            </div>
        </div>
        
        <!-- Channel Keys (v4.0.0) -->
        <div class="card mb-4" id="channel-keys">
            <div class="card-header">
                <h5 class="mb-0">
                    <i class="bi bi-broadcast me-2"></i>Channel Keys
                    <span class="badge bg-info ms-2">v4.1</span>
                </h5>
            </div>
            <div class="card-body">
                <p>
                    Channel keys provide <strong>deployment/group isolation</strong>. Messages encoded with one channel key 
                    cannot be decoded with a different key, even if all other credentials match.
                </p>
                
                <div class="row mt-4">
                    <!-- Auto Mode -->
                    <div class="col-md-4 mb-3">
                        <div class="card bg-dark h-100">
                            <div class="card-header text-center">
                                <i class="bi bi-gear-fill text-success fs-2 d-block mb-2"></i>
                                <strong>Auto</strong>
                            </div>
                            <div class="card-body">
                                <p class="small mb-2">Uses server-configured key if available, otherwise public mode.</p>
                                <ul class="small mb-0">
                                    <li>Server admin configures the shared key</li>
                                    <li>All users share the same channel</li>
                                </ul>
                            </div>
                        </div>
                    </div>
                    
                    <!-- Public Mode -->
                    <div class="col-md-4 mb-3">
                        <div class="card bg-dark h-100">
                            <div class="card-header text-center">
                                <i class="bi bi-globe text-info fs-2 d-block mb-2"></i>
                                <strong>Public</strong>
                            </div>
                            <div class="card-body">
                                <p class="small mb-2">No channel key. Compatible with other public installations.</p>
                                <ul class="small mb-0">
                                    <li>Default if no server key configured</li>
                                    <li>Anyone can decode (with credentials)</li>
                                    <li>Interoperable between deployments</li>
                                </ul>
                            </div>
                        </div>
                    </div>
                    
                    <!-- Custom Mode -->
                    <div class="col-md-4 mb-3">
                        <div class="card bg-dark h-100">
                            <div class="card-header text-center">
                                <i class="bi bi-key-fill text-warning fs-2 d-block mb-2"></i>
                                <strong>Custom</strong>
                            </div>
                            <div class="card-body">
                                <p class="small mb-2">Your own group key. Share with recipients.</p>
                                <ul class="small mb-0">
                                    <li>Format: <code>XXXX-XXXX-XXXX-XXXX-XXXX-XXXX-XXXX-XXXX</code></li>
                                    <li>32 chars (128 bits entropy)</li>
                                    <li>Private group communication</li>
                                </ul>
                            </div>
                        </div>
                    </div>
                </div>
                
                {% if channel_configured %}
                <div class="alert alert-success mt-3 mb-0">
                    <i class="bi bi-shield-lock me-2"></i>
                    <strong>This server has a channel key configured:</strong>
                    <code class="ms-2">{{ channel_fingerprint }}</code>
                </div>
                {% else %}
                <div class="alert alert-info mt-3 mb-0">
                    <i class="bi bi-info-circle me-2"></i>
                    This server is running in <strong>public mode</strong>.
                    Set <code>STEGASOO_CHANNEL_KEY</code> to enable server-wide channel isolation.
                </div>
                {% endif %}
            </div>
        </div>
        
        <!-- Version History -->
        <div class="card mb-4">
            <div class="card-header">
                <h5 class="mb-0"><i class="bi bi-clock-history me-2"></i>Version History</h5>
            </div>
            <div class="card-body">
                <!-- Current Version - Prominent -->
                <div class="alert alert-success mb-4">
                    <div class="d-flex align-items-center">
                        <span class="badge bg-success fs-6 me-3">v4.2.1</span>
                        <div>
                            <strong>Security & API improvements:</strong>
                            API key authentication,
                            TLS with self-signed certs,
                            CLI tools (compress, rotate, convert),
                            jpegtran lossless JPEG rotation
                        </div>
                    </div>
                </div>

                <!-- Previous Versions - Accordion -->
                <div class="accordion" id="versionAccordion">
                    <div class="accordion-item bg-dark">
                        <h2 class="accordion-header">
                            <button class="accordion-button collapsed bg-dark text-light py-2" type="button"
                                    data-bs-toggle="collapse" data-bs-target="#olderVersions">
                                <i class="bi bi-archive me-2"></i>Previous Versions
                            </button>
                        </h2>
                        <div id="olderVersions" class="accordion-collapse collapse" data-bs-parent="#versionAccordion">
                            <div class="accordion-body p-0">
                                <table class="table table-dark table-sm small mb-0">
                                    <tbody>
                                        <tr>
                                            <td width="80"><strong>4.1.7</strong></td>
                                            <td>Progress bars for encode, mobile polish, release validation</td>
                                        </tr>
                                        <tr>
                                            <td width="80"><strong>4.1.1</strong></td>
                                            <td>DCT RS format stability, Docker cleanup, first-boot wizard</td>
                                        </tr>
                                        <tr>
                                            <td><strong>4.1.0</strong></td>
                                            <td>Reed-Solomon error correction for DCT, majority voting headers</td>
                                        </tr>
                                        <tr>
                                            <td><strong>4.0.0</strong></td>
                                            <td>Channel keys, DCT default, subprocess isolation</td>
                                        </tr>
                                        <tr>
                                            <td>3.2.0</td>
                                            <td>Single passphrase, more default words</td>
                                        </tr>
                                        <tr>
                                            <td>3.0.0</td>
                                            <td>DCT mode, JPEG output, color preservation</td>
                                        </tr>
                                        <tr>
                                            <td>2.x</td>
                                            <td>Web UI, REST API, RSA keys, QR codes, file embedding</td>
                                        </tr>
                                        <tr>
                                            <td>1.0.0</td>
                                            <td>Initial release, CLI only, LSB mode</td>
                                        </tr>
                                    </tbody>
                                </table>
                            </div>
                        </div>
                    </div>
                </div>
            </div>
        </div>
        
        <div class="card mb-4">
            <div class="card-header">
                <h5 class="mb-0"><i class="bi bi-question-circle me-2"></i>Usage Guide</h5>
            </div>
            <div class="card-body">
                <div class="accordion" id="usageAccordion">
                    <div class="accordion-item bg-dark">
                        <h2 class="accordion-header">
                            <button class="accordion-button bg-dark text-light" type="button" 
                                    data-bs-toggle="collapse" data-bs-target="#setup">
                                <i class="bi bi-1-circle me-2"></i>Initial Setup
                            </button>
                        </h2>
                        <div id="setup" class="accordion-collapse collapse show" data-bs-parent="#usageAccordion">
                            <div class="accordion-body">
                                <ol>
                                    <li>Agree on a <strong>reference photo</strong> (never transmitted)</li>
                                    <li>Go to <a href="/generate">Generate</a> to create credentials</li>
                                    <li>Memorize passphrase and PIN</li>
                                    <li>If using RSA, store the key file securely</li>
                                    <li>Share credentials via secure channel</li>
                                </ol>
                            </div>
                        </div>
                    </div>
                    
                    <div class="accordion-item bg-dark">
                        <h2 class="accordion-header">
                            <button class="accordion-button collapsed bg-dark text-light" type="button" 
                                    data-bs-toggle="collapse" data-bs-target="#encoding">
                                <i class="bi bi-2-circle me-2"></i>Encoding
                            </button>
                        </h2>
                        <div id="encoding" class="accordion-collapse collapse" data-bs-parent="#usageAccordion">
                            <div class="accordion-body">
                                <ol>
                                    <li>Go to <a href="/encode">Encode</a></li>
                                    <li>Upload <strong>reference photo</strong> and <strong>carrier image</strong></li>
                                    <li>Choose mode:
                                        <ul>
                                            <li><strong>DCT</strong> (default): social media</li>
                                            <li><strong>LSB</strong>: email, cloud, direct transfer</li>
                                        </ul>
                                    </li>
                                    <li>Enter message or select file</li>
                                    <li>Enter passphrase and PIN/key</li>
                                    <li>Download stego image</li>
                                </ol>
                            </div>
                        </div>
                    </div>
                    
                    <div class="accordion-item bg-dark">
                        <h2 class="accordion-header">
                            <button class="accordion-button collapsed bg-dark text-light" type="button" 
                                    data-bs-toggle="collapse" data-bs-target="#decoding">
                                <i class="bi bi-3-circle me-2"></i>Decoding
                            </button>
                        </h2>
                        <div id="decoding" class="accordion-collapse collapse" data-bs-parent="#usageAccordion">
                            <div class="accordion-body">
                                <ol>
                                    <li>Go to <a href="/decode">Decode</a></li>
                                    <li>Upload <strong>reference photo</strong></li>
                                    <li>Upload <strong>stego image</strong></li>
                                    <li>Enter passphrase and PIN/key</li>
                                    <li>View message or download file</li>
                                </ol>
                                <div class="alert alert-info small mt-3 mb-0">
                                    <i class="bi bi-magic me-2"></i>
                                    Mode is auto-detected.
                                </div>
                            </div>
                        </div>
                    </div>
                </div>
            </div>
        </div>
        
        <div class="card mb-4">
            <div class="card-header">
                <h5 class="mb-0"><i class="bi bi-speedometer2 me-2"></i>Limits &amp; Specs</h5>
            </div>
            <div class="card-body">
                <!-- Key Specs - Always Visible -->
                <div class="row text-center mb-4">
                    <div class="col-6 col-md-4 col-lg-2 mb-3">
                        <div class="p-3 bg-dark rounded h-100">
                            <i class="bi bi-file-earmark text-primary fs-3 d-block mb-2"></i>
                            <div class="small text-muted">Max Payload</div>
                            <strong>{{ max_payload_kb }} KB</strong>
                        </div>
                    </div>
                    <div class="col-6 col-md-4 col-lg-2 mb-3">
                        <div class="p-3 bg-dark rounded h-100">
                            <i class="bi bi-image text-info fs-3 d-block mb-2"></i>
                            <div class="small text-muted">Max Carrier</div>
                            <strong>24 MP</strong>
                        </div>
                    </div>
                    <div class="col-6 col-md-4 col-lg-2 mb-3">
                        <div class="p-3 bg-dark rounded h-100">
                            <i class="bi bi-soundwave text-warning fs-3 d-block mb-2"></i>
                            <div class="small text-muted">DCT Capacity</div>
                            <strong>~75 KB/MP</strong>
                        </div>
                    </div>
                    <div class="col-6 col-md-4 col-lg-2 mb-3">
                        <div class="p-3 bg-dark rounded h-100">
                            <i class="bi bi-grid-3x3 text-success fs-3 d-block mb-2"></i>
                            <div class="small text-muted">LSB Capacity</div>
                            <strong>~375 KB/MP</strong>
                        </div>
                    </div>
                    <div class="col-6 col-md-4 col-lg-2 mb-3">
                        <div class="p-3 bg-dark rounded h-100">
                            <i class="bi bi-shield-check text-danger fs-3 d-block mb-2"></i>
                            <div class="small text-muted">Encryption</div>
                            <strong>AES-256</strong>
                        </div>
                    </div>
                    <div class="col-6 col-md-4 col-lg-2 mb-3">
                        <div class="p-3 bg-dark rounded h-100">
                            <i class="bi bi-bandaid text-info fs-3 d-block mb-2"></i>
                            <div class="small text-muted">DCT ECC</div>
                            <strong>RS Code</strong>
                        </div>
                    </div>
                </div>

                <!-- Error Correction Detail -->
                <div class="alert alert-info small mb-4">
                    <i class="bi bi-info-circle me-2"></i>
                    <strong>Reed-Solomon Error Correction:</strong> DCT mode corrects up to 16 byte errors per 223-byte chunk.
                    Handles problematic carrier images with uniform areas that cause unstable DCT coefficients.
                </div>

                <!-- More Specs - Accordion -->
                <div class="accordion" id="specsAccordion">
                    <div class="accordion-item bg-dark">
                        <h2 class="accordion-header">
                            <button class="accordion-button collapsed bg-dark text-light py-2" type="button"
                                    data-bs-toggle="collapse" data-bs-target="#moreSpecs">
                                <i class="bi bi-list-ul me-2"></i>More Specifications
                            </button>
                        </h2>
                        <div id="moreSpecs" class="accordion-collapse collapse" data-bs-parent="#specsAccordion">
                            <div class="accordion-body p-0">
                                <table class="table table-dark table-striped small mb-0">
                                    <tbody>
                                        <tr>
                                            <td><i class="bi bi-file-text me-2"></i>Max text</td>
                                            <td><strong>2M characters</strong></td>
                                        </tr>
                                        <tr>
                                            <td><i class="bi bi-upload me-2"></i>Max upload</td>
                                            <td><strong>30 MB</strong></td>
                                        </tr>
                                        <tr>
                                            <td><i class="bi bi-clock me-2"></i>File expiry</td>
                                            <td><strong>10 min</strong></td>
                                        </tr>
                                        <tr>
                                            <td><i class="bi bi-key me-2"></i>PIN</td>
                                            <td><strong>6-9 digits</strong></td>
                                        </tr>
                                        <tr>
                                            <td><i class="bi bi-shield me-2"></i>RSA keys</td>
                                            <td><strong>2048, 3072 bit</strong></td>
                                        </tr>
                                        <tr>
                                            <td><i class="bi bi-chat-quote me-2"></i>Passphrase</td>
                                            <td><strong>3-12 words</strong> (BIP-39)</td>
                                        </tr>
                                        <tr>
                                            <td><i class="bi bi-code me-2"></i>Python Version</td>
                                            <td><strong>3.10-3.12</strong></td>
                                        </tr>
                                        <tr>
                                            <td><i class="bi bi-box me-2"></i>Built with</td>
                                            <td>Flask, Pillow, NumPy, SciPy, jpegio, reedsolo, cryptography, argon2-cffi</td>
                                        </tr>
                                    </tbody>
                                </table>
                            </div>
                        </div>
                    </div>
                </div>
            </div>
        </div>
        
    </div>
</div>
{% endblock %}