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Tor Network

The Onion Router

18 min read Updated 2024

What Is Tor?

Tor (The Onion Router) is a decentralized network that anonymizes internet traffic by routing it through multiple encrypted relays. Originally developed by the US Naval Research Laboratory, now maintained by The Tor Project nonprofit.

How Onion Routing Works

Circuit Construction
Your traffic is encrypted in layers:

[Message]
  ↓ Encrypt with Exit key
[Layer 3]
  ↓ Encrypt with Middle key
[Layer 2]
  ↓ Encrypt with Guard key
[Layer 1]

Guard → Middle → Exit → Destination

Each relay peels one layer, knows only prev/next hop

Relay Types

Guard Relay

Entry point, stable and trusted

Entry

Middle Relay

Internal routing, low risk to run

Transit

Exit Relay

Connection to clearnet destinations

Exit

Bridge

Unlisted entry for censored users

Anti-censorship

Use Cases

  • Circumventing censorship
  • Whistleblowing and journalism
  • Privacy from ISP surveillance
  • Accessing .onion services
  • Protecting source identity

Limitations

Timing AttacksGlobal adversaries can correlate traffic
Exit MonitoringUnencrypted traffic visible at exit
Browser ExploitsJavaScript can deanonymize users
User ErrorLogging in, behavioral patterns