QKD Trusted-Node Relay Network

Relay Network

Relay nodes (Alice ↔ Bob) 3

Total fiber span 240 km

Per-node compromise risk 6%

Live Link Status

Bottleneck secure key rate

— kbit/s

P(entire chain uncompromised)

—

Compromised nodes right now

0 / 0

How it works

The no-cloning theorem forbids amplifying an unknown quantum state, so a classical optical repeater cannot boost a QKD signal the way it boosts ordinary telecom light. Two options exist to go beyond one fiber span (~100–200 km before the raw photon rate collapses): experimental quantum repeaters (entanglement swapping + purification), or the option already deployed today — trusted-node relays.

Hop transmittance: T(L) = 10^(-α·L / 10),  α ≈ 0.2 dB/km (telecom fiber)
Secure key rate:   R(L) ≈ R₀ · T(L)
Chain throughput:  R_chain = min(R_hop1, R_hop2, … , R_hopN)
Chain trust:       P(secure) = (1 − p)ⁿ  for n independent relays

Each relay node in this model fully decrypts the inbound one-time-pad-protected key and re-encrypts it with a fresh key generated on the next hop's own QKD link. That is exactly why the model is called "trusted": whoever controls that node's memory at the moment of relay can read the plaintext key. A single compromised relay breaks confidentiality for every message relayed through it afterwards — the End-to-end trust probability above falls geometrically with the number of hops, which is the real-world argument for keeping relay counts low or moving to entanglement-based repeaters for long-haul quantum networks.

Relay nodes — more hops shorten each fiber segment (less loss per hop) but add more places an adversary can compromise.
Fiber span — spreads the same physical distance across however many hops you chose; longer hops attenuate the signal exponentially, capping the bottleneck key rate.
Per-node compromise risk — the probability model used by "Roll trust dice"; it does not touch the current visual state until you roll.
Roll trust dice — independently compromises each relay node with that probability; the chain link turns red from the first compromised node onward, since every following hop also passes through attacker-visible plaintext.

Secure key hop Exposed (past a compromised node) Trusted endpoint (Alice / Bob)

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