@causeway-sh/sapling

Zcash Sapling shielded helpers for Causeway. Bech32 z-address parse/encode plus high-level wrappers around the coordinator's BuildAndSignSaplingSpend and BroadcastSaplingTx RPCs. The whole shielded pipeline runs through the threshold operator quorum — your dApp never touches a spend-auth key or a Groth16 prover.

Install

pnpm add @causeway-sh/core@alpha @causeway-sh/sapling@alpha

Quickstart

import { GrpcWebCoordinatorClient } from "@causeway-sh/core";
import { sendToZaddr } from "@causeway-sh/sapling";

const coordinator = new GrpcWebCoordinatorClient({
  baseUrl: "https://coordinator.causeway.sh",
});

const result = await sendToZaddr({
  coordinator,
  to: "zs1q3qpr6wt3rzymfrg3pyzfmjny2synhk2ut9as6dyxqpvcdlq94jscze8pww28rnqyplzwz7hpjx",
  amountZat: 50_000n,
  feeZat: 15_000n,
});

console.log("broadcast txid:", result.broadcastTxid);
console.log("sighash:        ", result.sighashHex);

That's the entire shielded spend: coordinator builds the PCZT, runs the FROST-RedJubjub round across 5 of 7 operators, returns a broadcast-ready v5 transaction, and we send it to mainnet.

API

• bech32 z-address helpers — decodeSaplingAddress(s) and encodeSaplingAddress(network, raw43). Handles zs1… (mainnet), ztestsapling1… (testnet), and zregtestsapling1… (regtest). Strict bech32 (not bech32m) so mangled unified-address strings fail closed.
• sendToZaddr({...}) — end-to-end convenience: decode bech32, call the coordinator, broadcast via the coordinator's lightwalletd, return { broadcastTxid, sighashHex, rawTxHex }.
• fetchSaplingVaultAddress(coordinator) — ask the coordinator for the active vault's bech32 z-address + raw 43 bytes.
• zcashdRpcCall(...) — minimal JSON-RPC client for callers that want to broadcast through their own zcashd instead of the coordinator. fetch-based, works in Node 20+ and browsers (with CORS configured).

Why the SDK doesn't run Groth16

Sapling spend-auth signing requires the vault's nsk for the SNARK witness. In Causeway's threshold model that material lives only in the coordinator process and is never exposed to dApps or tenant programs. The SDK therefore never runs Groth16 — it asks the coordinator for a signed raw_tx and broadcasts it.

Status

Alpha. Real Sapling shielded mainnet broadcasts have completed end-to-end through this SDK. The on-chain program is unverified bytecode and the protocol is not audited. Do not move funds you can't afford to lose.

License

Apache-2.0

Links

• Repository — https://github.com/causeway-protocol/sdk-ts
• Protocol — https://causeway.sh