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docs/SECURITY.md

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+# Security Documentation
+
+## Overview
+This document outlines the security measures implemented in the Simple File Upload Server and provides guidelines for secure deployment and operation.
+
+## Security Features
+
+### Authentication
+1. **API Key Authentication**
+   - Required for all upload endpoints
+   - Configured via CLIENT_KEY environment variable
+   - Transmitted via X-Client-Key HTTP header
+   - No default keys allowed in production
+
+2. **Download Security**
+   - 6-digit alphanumeric codes
+   - One-time use downloads (configurable)
+   - Automatic expiration
+   - No directory listing
+
+### File Security
+
+1. **Upload Security**
+   - Secure filename sanitization
+   - No executable permissions
+   - Temporary storage with cleanup
+   - Chunked upload verification
+
+2. **Storage Security**
+   - Files stored outside web root
+   - Metadata separation from files
+   - Automatic cleanup of expired files
+   - Abandoned upload detection
+
+3. **Download Controls**
+   - Maximum download limits
+   - Expiry time enforcement
+   - Force download headers
+   - Content-Type verification
+
+### Network Security
+
+1. **SSL/TLS**
+   - Required for production
+   - Modern cipher configuration
+   - Perfect forward secrecy
+   - SSL certificate validation
+
+2. **Headers**
+   - Secure response headers
+   - No version disclosure
+   - XSS protection
+   - Content security policy
+
+## Secure Deployment
+
+### Production Requirements
+
+1. **SSL Configuration**
+```nginx
+ssl_protocols TLSv1.2 TLSv1.3;
+ssl_prefer_server_ciphers on;
+ssl_ciphers ECDHE-ECDSA-AES128-GCM-SHA256:ECDHE-RSA-AES128-GCM-SHA256:ECDHE-ECDSA-AES256-GCM-SHA384:ECDHE-RSA-AES256-GCM-SHA384:DHE-RSA-AES128-GCM-SHA256:DHE-RSA-AES256-GCM-SHA384;
+```
+
+2. **Environment Setup**
+```bash
+# Required settings
+export CLIENT_KEY="strong-random-key"
+export UPLOAD_FOLDER="/secure/path/uploads"
+
+# SSL settings
+export SSL_CERT="/path/to/cert.pem"
+export SSL_KEY="/path/to/key.pem"
+```
+
+3. **File Permissions**
+```bash
+# Storage directory
+chmod 750 /secure/path/uploads
+chown www-data:www-data /secure/path/uploads
+
+# SSL files
+chmod 600 /path/to/key.pem
+chmod 644 /path/to/cert.pem
+```
+
+### Docker Security
+
+1. **Container Configuration**
+   - Non-root user
+   - Read-only root filesystem
+   - Limited capabilities
+   - Resource limits
+
+2. **Volume Management**
+   - Separate volumes for uploads
+   - Proper permissions
+   - Regular cleanup
+   - Backup strategy
+
+## Security Monitoring
+
+### Logging
+
+1. **Access Logs**
+   - Upload attempts
+   - Download tracking
+   - Error logging
+   - Authentication failures
+
+2. **Audit Trail**
+   - File operations
+   - Configuration changes
+   - System events
+   - Cleanup activities
+
+### Monitoring Requirements
+
+1. **System Monitoring**
+   - Disk usage
+   - Memory utilization
+   - Network traffic
+   - Error rates
+
+2. **Security Alerts**
+   - Authentication failures
+   - Unusual activity
+   - Storage warnings
+   - SSL certificate expiry
+
+## Security Best Practices
+
+### Server Configuration
+
+1. **Firewall Rules**
+   - Allow only required ports
+   - Rate limit connections
+   - Block suspicious IPs
+   - Monitor access patterns
+
+2. **Process Isolation**
+   - Run as dedicated user
+   - Minimal permissions
+   - Resource limits
+   - Process supervision
+
+### Data Protection
+
+1. **File Handling**
+   - Validate file types
+   - Scan for malware
+   - Enforce size limits
+   - Secure deletion
+
+2. **Metadata Protection**
+   - Regular backups
+   - Access controls
+   - Data validation
+   - Secure storage
+
+## Future Security Enhancements
+
+### Planned Features
+
+1. **Rate Limiting**
+   - Per-IP limits
+   - Token bucket algorithm
+   - Configurable thresholds
+   - Automatic blocking
+
+2. **Advanced Authentication**
+   - API key rotation
+   - IP whitelisting
+   - Two-factor auth option
+   - Access tokens
+
+3. **Enhanced Monitoring**
+   - Real-time alerts
+   - Usage analytics
+   - Threat detection
+   - Performance tracking
+
+### Security Roadmap
+
+1. **Short Term**
+   - Implement rate limiting
+   - Add file type restrictions
+   - Enhance logging
+   - Add health checks
+
+2. **Long Term**
+   - Access audit system
+   - Advanced monitoring
+   - Automated backups
+   - High availability
+
+## Incident Response
+
+### Response Plan
+
+1. **Detection**
+   - Monitor logs
+   - Track metrics
+   - Alert on anomalies
+   - User reports
+
+2. **Response**
+   - Assess impact
+   - Contain threat
+   - Notify stakeholders
+   - Document incident
+
+3. **Recovery**
+   - Restore service
+   - Update security
+   - Review procedures
+   - Implement fixes
+
+### Security Contacts
+
+For security issues or vulnerabilities:
+1. Create a GitHub issue with [SECURITY] prefix
+2. For critical issues, contact maintainers directly
+3. Follow responsible disclosure guidelines
+4. Allow time for patches before public disclosure