Anonymization and Onion Routing

Overview of Onion Routing

• Onion routing is a technique for achieving anonymity over the internet.
• Tor (The Onion Router) is an implementation of onion routing, developed by US Naval Research in the mid-90s.
• Focus on the distinction between anonymity and confidentiality:
  • Anonymity: Hiding the identity of the sender.
  • Confidentiality: Hiding the content of the communication (encryption).

How Onion Routing Works

• Communication is routed through multiple layers of encryption (like an onion).
• The sender’s identity is hidden from the servers they communicate with.
• A typical setup involves:
  • Client communicates with a server through multiple hops (intermediate nodes).
  • Each hop knows only its immediate predecessor and successor, not the entire route.

Key Components of Onion Routing

• Multiple Hops: Tor typically uses three hops.
• Encryption Layers: Messages are encrypted multiple times before being sent through the network.
  • Each intermediate node removes one layer of encryption.
  • Only the final node knows the actual content of the message.

The Process of Connecting to a Server

1. Establish a circuit with three nodes.
2. Encrypt the message three times using shared symmetric keys (K1, K2, K3):
   • K1: First hop
   • K2: Second hop
   • K3: Final hop
3. Each node decrypts its layer and forwards the message to the next node.
4. The final hop accesses the server on behalf of the client.
5. Responses are sent back in reverse order (adding encryption layers back).

Benefits of Onion Routing

• Anonymity: No individual node knows the full path of the message, enhancing privacy.
• Traffic Analysis Prevention: Each node only knows the next hop and the previous hop, making it difficult for attackers to de-anonymize users.
• Static Message Size: Tor messages are always 512 bytes, preventing size-based analysis.

Challenges and Limitations

• Speed: The multiple hops can slow down communication due to distance and shared bandwidth.
• Potential for Traffic Analysis: If an attacker controls both the entry and exit nodes, they can potentially correlate traffic and de-anonymize users.
• Vigilance Required: Users need to maintain good security practices, such as using TLS or HTTPS, to protect their data once it leaves the Tor network.

Conclusion

• Tor provides a powerful tool for anonymity but is not foolproof.
• Understanding how onion routing works is crucial for grasping the benefits and limitations of using Tor.