Zcash × Nym

Mixnet via exit proxy (IP packet router) — single IPR

Fixed-size Sphinx packets, three mix layers with per-hop delays, Poisson sending with cover, then an exit-side IP packet router to a stock lightwalletd. Strong against network observers; against the destination a fixed IPR behaves like dVPN single-exit.

✅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 GWIPRlightwalletd
ClientEntry GWMixExit GWIPRlightwalletd
Mixnet (5-hop) (mixing delays)

Per-actor assessment & trade-offs

L2Compromised lightwalletd✅P1❌P2

Sees

  • Exit gateway / IPR IP
  • All requests and contents

Can't see

  • Client IP

Residual / countermeasure

  • The wallet's TCP connection to lightwalletd is an ordinary end-to-end connection arriving from the exit's IP. Per-packet unlinkability in transit does not translate into request unlinkability at the destination.
  • With a fixed IPR, P2 behaves exactly like the dVPN single-exit case — rotate the IPR per request to restore it (see the rotating-IPR scenario).
L3LLocal network observer✅P1

Sees

  • Constant-size packets at a Poisson rate with cover traffic
  • That the client uses the Nym mixnet

Can't see

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

Sees

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

Residual / countermeasure

  • The extent to which bulk transfers of many packets can be correlated over time is an open question. The mixnet is strongest for small, independent messages and weakest for bulk sync — one reason bulk sync does not belong on the mixnet (the other is throughput).

Pros

  • Client IP heavily obfuscated (timing + location) by the Nym network

Cons / mitigations

  • Compact-block sync very slow (5-hop + mixing delays)
  • Fixed IPR is a linking key at the destination

Fit

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

Latency model

Regional (40)Continental (120)Intercontinental (300)
Mixnet (5-hop)1.9 s (7 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).