onion routing

A technique that routes traffic through multiple encrypted layers, each removing one layer of encryption (like peeling an onion) as data passes through successive nodes. Tor uses onion routing to hide both sender identity and destination from intermediate observers. Each node knows only the previous and next hop, so no single point in the chain can correlate source and destination. The layers are nested during circuit construction—the originating client encrypts the message multiple times in reverse order of nodes, so decryption happens in the correct sequence. This is why .onion addresses exist: they're hidden services that advertise their Tor circuit path encrypted, allowing connection without directory server leaks. Onion routing doesn't guarantee anonymity against global passive adversaries or endpoint attacks, but it makes casual traffic analysis and ISP-level snooping substantially harder. It's the core reason Tor exists, and why bundled domain registrations over Tor (anonymous signup, no WHOIS leaks) remain valuable—the circuit obscures your IP from the registrar's perspective, though payment still reveals identity if you use a traceable method.