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Install the SDK

If you haven’t already, install the SDK and set up your environment
 The Dryja-Poon construction enables bidirectional payment channels with revocation-based state updates.
PathConditionWhen to use
Funding (collaborative)Alice + Bob + server signaturesOpen channel instantly
Funding (unilateral)Alice + Bob signatures (after exit delay)Fallback if server unresponsive
To-local (revocation)Counterparty revocation signaturePunish old state broadcast
To-local (normal)Self signature (after CSV delay)Claim own balance
To-remoteCounterparty signatureImmediate claim

​
Build the Tapscript

import { Script } from '@scure/btc-signer';
import { hex } from '@scure/base';
import {
  RestArkProvider,
  SingleKey,
  VtxoScript,
  networks
} from '@arkade-os/sdk';

// Setup
const arkProvider = new RestArkProvider('https://mutinynet.arkade.sh');
const info = await arkProvider.getInfo();
const serverPubkey = hex.decode(info.signerPubkey).slice(1); // x-only
const exitDelay = BigInt(info.exitDelay);

// Channel participants
const alice = SingleKey.fromRandomBytes();
const bob = SingleKey.fromRandomBytes();
const alicePubkey = await alice.xOnlyPublicKey();
const bobPubkey = await bob.xOnlyPublicKey();

// Standard Lightning CSV delay for to_local
const toLocalDelay = 144n; // ~1 day in blocks

​
Funding output

2-of-2 multisig between Alice and Bob, with Ark timeout path: 
Collaborative: <alicePubkey> OP_CHECKSIGVERIFY <bobPubkey> OP_CHECKSIGVERIFY <serverPubkey> OP_CHECKSIG
Unilateral:    <exitDelay> OP_CSV OP_DROP <alicePubkey> OP_CHECKSIGVERIFY <bobPubkey> OP_CHECKSIG

// Collaborative: aliceSig + bobSig + serverSig
const fundingCollaborative = Script.encode([
  alicePubkey,
  'CHECKSIGVERIFY',
  bobPubkey,
  'CHECKSIGVERIFY',
  serverPubkey,
  'CHECKSIG'
]);

// Unilateral: after exitDelay, aliceSig + bobSig
const fundingUnilateral = Script.encode([
  exitDelay,
  'CHECKSEQUENCEVERIFY',
  'DROP',
  alicePubkey,
  'CHECKSIGVERIFY',
  bobPubkey,
  'CHECKSIG'
]);

const fundingScript = new VtxoScript([fundingCollaborative, fundingUnilateral]);
const fundingAddress = fundingScript.address(networks.mutinynet.hrp, serverPubkey).encode();

console.log('Funding address:', fundingAddress);

​
To-local output (commitment transaction)

Funds belonging to the broadcaster, with revocation for punishment: 
Revocation: <revocationPubkey> OP_CHECKSIG
Normal:     <toLocalDelay> OP_CSV OP_DROP <localPubkey> OP_CHECKSIG

// Revocation keys are derived per commitment (simplified here)
function buildToLocalScript(
  localPubkey: Uint8Array,
  revocationPubkey: Uint8Array,
  delay: bigint
) {
  // Revocation path: counterparty can punish old state
  const revocationPath = Script.encode([
    revocationPubkey,
    'CHECKSIG'
  ]);

  // Normal path: broadcaster claims after delay
  const normalPath = Script.encode([
    delay,
    'CHECKSEQUENCEVERIFY',
    'DROP',
    localPubkey,
    'CHECKSIG'
  ]);

  // Ark unilateral exit variant
  const unilateralPath = Script.encode([
    exitDelay,
    'CHECKSEQUENCEVERIFY',
    'DROP',
    delay,
    'CHECKSEQUENCEVERIFY',
    'DROP',
    localPubkey,
    'CHECKSIG'
  ]);

  return new VtxoScript([revocationPath, normalPath, unilateralPath]);
}

// Alice's to_local in her commitment
const aliceRevocationPubkey = /* derived from Bob's revocation basepoint */;
const aliceToLocal = buildToLocalScript(alicePubkey, aliceRevocationPubkey, toLocalDelay);

​
To-remote output (commitment transaction)

Funds belonging to the counterparty, immediately spendable: 
Normal:     <remotePubkey> OP_CHECKSIG
Unilateral: <exitDelay> OP_CSV OP_DROP <remotePubkey> OP_CHECKSIG

function buildToRemoteScript(remotePubkey: Uint8Array) {
  // Normal: counterparty claims immediately
  const normalPath = Script.encode([
    remotePubkey,
    'CHECKSIG'
  ]);

  // Ark unilateral exit
  const unilateralPath = Script.encode([
    exitDelay,
    'CHECKSEQUENCEVERIFY',
    'DROP',
    remotePubkey,
    'CHECKSIG'
  ]);

  return new VtxoScript([normalPath, unilateralPath]);
}

// Bob's to_remote in Alice's commitment
const bobToRemote = buildToRemoteScript(bobPubkey);

​
The dual-path pattern

Every Lightning script gets two Taproot leaves: 
Taproot tree:
├── <standard lightning script>
└── <exitDelay> OP_CSV OP_DROP <standard lightning script>
The first leaf is vanilla Lightning. The second adds a CSV delay matching the Batch expiry for Ark unilateral exit. The server’s key never appears in commitment or HTLC scripts.

​
Script breakdown

OpcodeEffect
CHECKSIGVerify signature, return result
CHECKSIGVERIFYVerify signature, continue if valid
CHECKSEQUENCEVERIFYEnforce relative timelock (CSV)
DROPRemove top stack element

​
Next steps

Lightning Channels

Full channel lifecycle on Arkade

Hashlock contract

Add hash conditions for HTLCs

Spilman channel

Simpler unidirectional channels

Deep dive

Learn about VTXOs and timelocks