@causeway-sh/btc

Bitcoin off-chain helpers for Causeway. P2TR (Taproot key-spend) vault addresses, BIP-341 sighash construction, witness assembly, and a small bitcoind JSON-RPC client.

Install

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

Quickstart

import {
  deriveVaultAddress,
  buildUnsignedTx,
  assembleSignedTx,
  BitcoindRpcClient,
} from "@causeway-sh/btc";

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.address); // "bc1p…"

const { unsignedTx, sighash } = buildUnsignedTx({ /* ... */ });

// run threshold Schnorr signing round on `sighash`,
// receive a 64-byte signature, then:
const signedRawTx = assembleSignedTx({ tx: unsignedTx, schnorrSignature });

const rpc = new BitcoindRpcClient({ url: "...", auth: "..." });
const txid = await rpc.sendRawTransaction(signedRawTx);

API

• deriveVaultAddress({ vaultThresholdPubkey, tenant, derivationPath, network }) — Causeway tweak → BIP-341 TapTweak → bech32m. Returns { address, outputKey, internalKey }. network: "mainnet" | "testnet4".
• buildUnsignedTx(plan) — single-input single-output unsigned tx plus the 32-byte BIP-341 key-spend sighash.
• assembleSignedTx({ tx, schnorrSignature }) — splice the 64-byte Schnorr signature into the input-0 witness; returns raw bytes ready for sendrawtransaction.
• BitcoindRpcClient — minimal sendrawtransaction / gettxout / getblockcount JSON-RPC client.

Scope

M1 shape: single-input, single-output, P2TR key-spend. No multi-input UTXO selection, no fee estimation. Use a fee oracle of your choice and pass the totals into buildUnsignedTx.

Status

Alpha. Bitcoin 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