Tor and Anonymity Systems

Tor and other anonymity systems are a class of tools and protocols within computer science designed to conceal a user's identity and online activities from surveillance and traffic analysis. The most famous of these, Tor, operates on the principle of "onion routing," where user traffic is wrapped in multiple layers of encryption and relayed through a distributed, worldwide network of volunteer-run servers. Each relay, or node, in the path decrypts only one layer to reveal the next hop, meaning no single point in the circuit knows both the original source and the final destination. This cybersecurity mechanism effectively severs the direct link between a user and the services they access, providing a powerful means for journalists, activists, and private citizens to protect their privacy and circumvent censorship.

1. Introduction to Anonymity and Privacy
   1. Fundamental Concepts
      1. Anonymity
         1. Definition and Properties
         2. Degrees of Anonymity
         3. Anonymity Sets
      2. Pseudonymity
         1. Persistent Identities
         2. Linkable vs Unlinkable Pseudonyms
      3. Unlinkability
         1. Action Unlinkability
         2. Identity Unlinkability
      4. Unobservability
         1. Traffic Unobservability
         2. Content Unobservability
   2. Privacy vs Anonymity Distinction
      1. Data Privacy
      2. Identity Privacy
      3. Behavioral Privacy
   3. Motivations for Online Anonymity
      1. Protection from Surveillance
         1. Government Surveillance
         2. Corporate Surveillance
         3. Mass Data Collection
      2. Circumvention of Censorship
         1. Accessing Blocked Content
         2. Bypassing Regional Restrictions
         3. Information Freedom
      3. Whistleblowing and Journalism
         1. Source Protection
         2. Secure Communication Channels
         3. Investigative Reporting
      4. Personal Privacy
         1. Avoiding Behavioral Profiling
         2. Preventing Data Aggregation
         3. Location Privacy
      5. Political Dissent
         1. Authoritarian Regimes
         2. Protest Organization
         3. Free Expression
   4. Threats to Online Anonymity
      1. Network-Level Threats
         1. Traffic Analysis
            1. Passive Traffic Analysis
            2. Active Traffic Analysis
            3. Statistical Analysis
         2. Eavesdropping
            1. Network Packet Capture
            2. Man-in-the-Middle Attacks
            3. SSL/TLS Interception
         3. IP Address Tracking
            1. Direct IP Logging
            2. IP-based Geolocation
            3. ISP Cooperation
      2. Application-Level Threats
         1. Browser Fingerprinting
            1. Device Fingerprinting
            2. Canvas Fingerprinting
            3. Font Enumeration
            4. WebRTC Leaks
         2. Tracking Technologies
            1. HTTP Cookies
            2. Supercookies
            3. Web Beacons
            4. Local Storage
      3. Correlation Attacks
         1. Timing Correlation
         2. Content Correlation
         3. Behavioral Correlation
      4. Social Engineering
         1. Information Disclosure
         2. Identity Correlation