Onion Routing: Layered Encryption & Traffic Correlation Defense

Network

Relay hops 3

Real traffic rate 6 pkt/s

Defenses

Cover traffic (padding) 40%

Timing jitter per hop 30 ms

Live Readouts

Packets in flight

Real : cover ratio

1 : 0.4

Attacker correlation confidence

—%

Est. end-to-end latency

— ms

Onion-encrypted hop (layers remaining) Cleartext hop (exit → destination) Cover / dummy packet Adversary vantage point (entry + exit)

How it works

The client wraps the message in one encryption layer per relay, innermost-first, using a session key each relay negotiated in a handshake the client alone can unwrap in order:

C = Enc_g( Enc_m1( … Enc_e( M ) … ) )
hop i strips exactly one Enc_k layer with its own key k
only the exit relay ever sees plaintext M

That is the confidentiality half of the model. The harder problem is traffic-correlation deanonymization: an adversary who watches both the entry relay and the exit relay never needs to break the crypto — matching the timing pattern of packets entering the network against packets leaving it is often enough to link sender and receiver. This simulator scores that risk with a simplified confidence model:

realFraction  = 1 / (1 + coverRate/realRate)
jitterFactor  = e^(-jitter_ms / 80)
hopFactor     = 0.65^(hops − 1)
confidence    = realFraction × jitterFactor × hopFactor

Relay hops — each additional independent relay adds its own queuing/latency noise, compounding the difficulty of matching entry and exit timing (hopFactor).
Real traffic rate — how often the client emits genuine packets, shown as gold-to-cyan spheres shedding one layer per hop.
Cover traffic — decoy packets (gray) indistinguishable from real ones to an outside observer; more cover traffic dilutes the fraction of flow that is genuine signal.
Timing jitter — random per-hop delay that blurs inter-packet gaps, the classic defense against timing correlation (and the reason low-latency anonymity networks trade some speed for it).

Real Tor-like networks use the ntor handshake for the per-hop keys and measure correlation with far richer statistical tests; the formula above keeps the same defensive levers — more hops, more cover traffic, more jitter — but simplifies them into one readable number for teaching.

Guard & exit are the adversary's vantage points Onion-encrypted Cleartext (post-exit)

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