@causeway-sh/zec

Zcash transparent off-chain helpers for Causeway. t-address derivation, ZIP-244 v5 sighash, scriptSig assembly, and a small lightwalletd gRPC-Web client. Hand-rolled in TypeScript — no WASM bridge required.

For shielded Sapling spends see @causeway-sh/sapling.

Install

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

Quickstart

import {
  deriveVaultAddress,
  buildUnsignedTx,
  assembleSignedTx,
  lowSNormalizeDer,
  LightwalletdClient,
} from "@causeway-sh/zec";

const v = deriveVaultAddress({
  vaultThresholdPubkey, // 33 bytes — from the on-chain Vault account
  tenant,               // 32 bytes — the tenant program's id
  derivationPath,       // canonical Causeway path bytes
  network: "mainnet",
});
console.log(v.tAddress); // "t1…"

const { unsignedTxBytes, sighash } = buildUnsignedTx({ /* ZecSendPlan */ });

// run threshold ECDSA signing round on `sighash`,
// receive a DER signature, low-S normalize, then splice:
const der = lowSNormalizeDer(rawDer);
const signedTx = assembleSignedTx({
  unsignedTxBytes,
  derSignature: der,
  compressedPubkey: v.tweakedPubkey,
});

const lwd = new LightwalletdClient({ baseUrl: "https://zec.rocks:443" });
const txid = await lwd.sendTransaction(signedTx);

API

• deriveVaultAddress({ vaultThresholdPubkey, tenant, derivationPath, network }) — Causeway tweak → HASH160 → Base58Check. network: "mainnet" | "testnet" | "regtest". Returns { tAddress, pkh, tweakedPubkey }.
• buildUnsignedTx(plan: ZecSendPlan) — unsigned v5 transparent tx bytes plus the 32-byte ZIP-244 sighash.
• assembleSignedTx({ unsignedTxBytes, derSignature, compressedPubkey }) — splice <DER+SIGHASH_ALL> <push 33 pubkey> scriptSig into the empty input-0 slot.
• lowSNormalizeDer(der) — normalize a DER-encoded ECDSA signature to BIP-146 low-S form.
• LightwalletdClient — minimal gRPC-Web client for GetLightdInfo, GetAddressUtxos, and SendTransaction.

Scope

M1 shape: single-input, single-output transparent spends. No multi-UTXO selection, no fee estimation.

Status

Alpha. Zcash mainnet transparent 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