Zcash × Nym

Mixnet via IPR — rotating (multipath) exits

The same mixnet path, but block chunks and broadcasts are spread across several exit IPRs from one entry gateway. Rotating the IPR per request restores unlinkability at the destination — the mixnet analogue of multi-exit dVPN. Still slow.

✅IP hidden · P1@L2✅Req-unlink · P2@L2✅Local net · P1@L3L◐Global net · P1@L3G❌Fast sync
Mixnet (5-hop)
Mix L1+50 msMix L2+50 msMix L3+50 msClientEntry GWExit AExit BExit Clightwalletd

One client and entry gateway; block chunks are requested from several exit gateways over the mixnet, all reaching one lightwalletd. Responses return through varied mixnet paths (via different exit gateways).

ClientEntry GWMixExit GWlightwalletd
Mixnet (5-hop) (mixing delays)

Per-actor assessment & trade-offs

L2Compromised lightwalletd✅P1✅P2

Sees

  • Requests from many exit gateways, with timing delays

Can't see

  • Client IP
  • A complete per-client profile

Residual / countermeasure

  • Against the destination this is the same as multi-exit dVPN with mixing added: fixed IPR = weaker (behaves like dVPN single-exit), rotating IPR = P2 restored. The anonymity set is all clients reaching that lightwalletd via Nym.
  • Intersection attacks across exit gateways over long-running syncs remain; few users per exit shrinks the anonymity set.
L3LLocal network observer✅P1

Sees

  • Constant-size packets at a Poisson rate with cover traffic

Can't see

  • Reliable destination, volume or activity
L3GGlobal network observer◐P1

Sees

  • Per-packet timing (hampered by mixing and cover)

Residual / countermeasure

  • Long bulk flows weaken per-packet correlation resistance (open question).

Pros

  • lightwalletd sees traffic from all Nym exit gateways, not the client

Cons / mitigations

  • Slow (5-hop + mixing delays)

Fit

  • Client identity + IP heavily hidden from lightwalletd
  • Block sync very slow

Latency model

Regional (40)Continental (120)Intercontinental (300)
Exit A · Mixnet (5-hop)1.6 s (6 hops, 3 mix layers)
Exit B · Mixnet (5-hop)1.6 s (6 hops, 3 mix layers)
Exit C · Mixnet (5-hop)1.6 s (6 hops, 3 mix layers)
Geographic propagation (speed-of-light)Per-hop mixing delayReliable-channel ACK (return, geographic only)Fragmentation (bounded send rate)

Fragmentation latency shown for SendTransaction (2.1 KB): a larger message splits into more Sphinx packets, metered onto the mixnet at a bounded rate, adding latency.

Baseline hygiene applies here tooWhatever the transport, the wallet still owes the same Layer-2 discipline: randomize request times, obfuscate the start height, and never broadcast on reaching the tip.Full detail →

Content from the Nym × Zcash reference doc. Latency figures are an illustrative model (not measured).