Nym mixnet now live in Zcash wallets

Today Nym is proud to share that it has completed its Zcash Community Grant, and the work is live where it matters most: the Nym mixnet is now live inside Zcash wallets. Since 2024, Nym's engineers and researchers have worked hand in hand with Zcash developers, including the legendary Daira-Emma Hopwood, to protect the one layer that even Zcash's celebrated zero-knowledge can't shield: the network traffic beneath every Zcash transaction.

Combining network-level and blockchain-level privacy for Zcash is what Nym and the Zcash community set out to build together, and it's finally in the hands of real users. Zcash's shielded transactions already hide what you send. Now the Nym mixnet can hide the person sending it.

The network layer Zcash leaves exposed

Zcash's zero-knowledge proofs are state of the art at protecting what happens on the chain. A shielded transaction hides the sender, the receiver, and the amount. What zk-SNARKs were never meant to protect is the network layer underneath: the stream of internet packets your wallet sends every time it syncs or broadcasts a transaction.

At that layer, your IP address, your timing, and your traffic patterns are exposed to your lightwalletd server, your internet provider, node operators, and anyone with a wide enough view of the network. Combine that network metadata with public blockchain data and a determined observer can start to link a "shielded" user back to their activity. On-chain privacy is simply not the same as anonymity. The gap isn't a Zcash flaw; it was acknowledged in Zcash's own founding Zerocash paper.

"Given that Zerocash transactions are not low latency themselves, Mixnets (e.g., Mixminion) are also a viable way to add anonymity, and one that is not as vulnerable to traffic analysis as Tor." — The original Zerocash paper, 2014

What Nym delivered

The grant produced a complete, developer-ready foundation for routing Zcash traffic through the Nym mixnet, where identically sized packets, randomized hops, and cover traffic make network metadata analysis impossible even for an adversary watching the whole network. Every piece is public, documented, and already being used.

A threat model and design guide for Zcash

Nym built a full network privacy threat model and design document for Zcash, reviewed with Nym's network of privacy experts and with Zcash's own developers. It maps the real threats a Zcash user faces, from a compromised lightwallet server to a global passive adversary watching the entire internet, and gives developers a concrete Nym-based remediation for each one, complete with animated diagrams.

It's the map every wallet developer needs to reason about network privacy, and the full threat model and design documentation for Zcash is public now at zcash-sdk.nym.com. The integration code was independently reviewed by Zcash cryptographer Daira-Emma Hopwood.

A toolkit for routing Zcash traffic through the mixnet

Not every wallet has the same needs. Sending a transaction is quick; syncing the whole chain is heavy. So rather than one rigid solution, Nym shipped a set of open-source Rust crates, all available on crates.io, that let developers pick the right protection for each kind of traffic:

• nym-smolmix is the key crate for existing wallets. It routes a wallet's ordinary HTTP(S) and gRPC traffic through the mixnet with a drop-in replacement for standard network sockets, so developers get mixnet protection without redesigning how their wallet talks to the network.
• nym-smoldvpn lets wallets sync chain information quickly but more privately, through a two-hop userspace WireGuard tunnel-in-a-tunnel.
• nym-swizzle adds traffic-pattern hygiene, shaping the timing and content of requests before they ever leave your device. It works the same whether traffic then travels over the mixnet, a VPN, Tor, or a direct connection.
• nym-swizzle-zcash tunes that hygiene specifically for Zcash's timing and block times, and ships with bindings for Go and C so it can drop into wallets written in any language.

Together they de-link a user's network identity from their Zcash activity: the endpoint still receives the transaction, but it can no longer see who or where it came from.

Zcash services that live inside the mixnet

For teams that want to go further, Nym built a way to run Zcash infrastructure inside the mixnet itself. Using the new nym-sdk::Stream module, a transaction-submission service can be reached only through the mixnet and stay invisible to the open internet, much like a hidden service for Zcash transactions.

Nym also documented how to run lightwalletd, the server most light wallets rely on, as one of these in-mixnet service providers, so protection can be built into the infrastructure and not just the app. See the instructions for running lightwalletd inside the Nym mixnet at zcash-sdk.nym.com.

Nym is already live in Zcash wallets

This isn't a proof of concept sitting on a shelf. Wallet developers are already shipping it.

Zingo! Wallet

Zingo has integrated the Nym mixnet natively, with the simple on-off switch Nym envisioned in the original grant.

➤ See more from Zingo!