Onion routing is a method for anonymising internet traffic by wrapping data in successive layers of encryption, much like the layers of an onion. Each encrypted layer is removed as the data passes through a series of independent servers called nodes or relays, with no single node knowing both the origin and destination of the traffic.
The most widely used implementation is Tor (The Onion Router), a free software network that volunteers run across the globe. When you send data through Tor, your message gets encrypted multiple times. The first relay only knows your identity but not your destination. The middle relays know neither. The final relay knows your destination but not your identity.
Why it matters: Onion routing protects against surveillance, censorship, and traffic analysis. Journalists, activists, and people living under oppressive regimes use it to communicate safely. It also helps protect privacy from your internet service provider, government agencies, and malicious actors monitoring network traffic.
Common gotchas: Onion routing slows connections noticeably because data travels through multiple hops. Exit node operators can theoretically see unencrypted traffic leaving the network if you do not use HTTPS. Your anonymity depends on the overall network size, so using Tor during unusual times reduces anonymity. Some websites block Tor users.
Onion routing does not hide the fact that you are using it, and in some countries using anonymity tools attracts suspicion. For strong privacy, pair it with other security measures like VPNs or HTTPS.