Onion Routing

Onion routing wraps a message in nested encryption layers, one for each relay in the path. As the message travels, each relay strips off the outermost layer using its key, learns only the next hop, and forwards the inner ciphertext. The first relay knows your identity but not your destination; the last knows the destination but not your identity. No single relay sees both ends. Tor is the most famous onion network, with ~7,000 volunteer relays. Session uses its own onion network (Service Nodes) for messaging. I2P is another onion-routed network with different design tradeoffs. The strength of onion routing is that it requires multiple relays to collude — and ideally multiple jurisdictions — to break anonymity. The weakness is that a global passive adversary watching both ends can correlate traffic timing. Onion routing is not magic; it is a probability game. Higher hop count and more diverse relay operators raise the cost of breaking it.