Onion Routing
Definition
A technique in which a message is encrypted in multiple layers, one per relay node, so that each relay decrypts only its own layer, forwards the remainder, and learns only its immediate predecessor and successor in the chain. Tor uses this design to prevent any single node from knowing both the sender and the destination.
- Core mechanism
- Message encrypted in layers, one per relay
- Visibility per node
- Only immediate predecessor and successor
- Primary implementation
- Tor network
Common questions
What does each relay in the chain actually learn about the traffic?+
A relay can see which node sent it the packet and which node it must forward the packet to next, but it cannot see the original sender, the final destination, or the decrypted content unless it is the exit node.
Why is onion routing hard for investigators to trace end to end?+
No single relay holds enough information to link sender and destination, so tracing a connection typically requires correlating traffic timing across multiple points on the network or compromising several relays in the same circuit.
Related terms
- Blockchain Analysis
- The forensic examination of a cryptocurrency's public transaction ledger to trace the flow of funds between addresses, cluster addresses controlled by the...
- Exit Node
- The third relay in a Tor circuit, which forwards decrypted traffic to the public internet destination. The destination server sees the exit...
- I2P (Invisible Internet Project)
- A peer-to-peer anonymity network that routes traffic through a distributed mesh of volunteer nodes using unidirectional tunnels. Unlike Tor, I2P is primarily...
- Onion Service (Hidden Service)
- A server reachable through Tor using a .onion address derived from its public key. The server's real IP address is never exposed...
- Traffic Correlation Attack
- A deanonymisation technique that compares timing patterns and traffic volume at the entry point of a Tor circuit and at the destination,...