Address

A VTXO is locked by a P2TR script composed of collaborative and exit script paths - the key path is always the unspendable key 0250929b74c1a04954b78b4b6035e97a5e078a5a0f28ec96d547bfee9ace803ac0.

An Ark address is the bech32m encoding of a prefix, the P2TR output key, and the server's x-only public key.

on mainnet, the address prefix is ark, while on test networks the prefix is always tark. For instance:

• P2TR output key: 25a43cecfa0e1b1a4f72d64ad15f4cfa7a84d0723e8511c969aa543638ea9967
• Server public key: 33ffb3dee353b1a9ebe4ced64b946238d0a4ac364f275d771da6ad2445d07ae0

mainnet: ark1x0lm8hhr2wc6n6lyemtyh9rz8rg2ftpkfun46aca56kjg3ws0tsztfpuanaquxc6faedvjk3tax0575y6perapg3e95654pk8r4fjec4q8efp
testnet: tark1x0lm8hhr2wc6n6lyemtyh9rz8rg2ftpkfun46aca56kjg3ws0tsztfpuanaquxc6faedvjk3tax0575y6perapg3e95654pk8r4fjecs5fyd2

tip

Like Bitcoin, the taproot tree encoded in the ark address is revealed only when the VTXO is spent. If it doesn't pass the server's validation, the owner won't be allowed to spend the VTXO off-chain. The unilateral exit would be the only option.

Code Examples

TypeScript

address.ts

import { Script, ScriptNum, p2tr, taprootListToTree } from '@scure/btc-signer'
import { TAPROOT_UNSPENDABLE_KEY } from '@scure/btc-signer/utils'
import { bech32m } from 'bech32'
import * as bip68 from 'bip68'


/**
 * Creates a default mainnet Ark address with collaborative and exit script paths
 * @param serverPubKey - Server's x-only public key (32 bytes)
 * @param myPubKey - User's x-only public key (32 bytes)
 * @param exitDelay - Number of blocks required for unilateral exit
 * @returns bech32m encoded Ark address
 */
function makeDefaultArkAddress(
  serverPubKey: XOnlyPubKey,
  myPubKey: XOnlyPubKey,
  timelock: number,
  isTestnet: boolean
): string {
  // create collaborative spending path
  const forfeit = Script.decode([
    serverPubKey,
    'CHECKSIGVERIFY',
    myPubKey,
    'CHECKSIG'
  ])
  
  // encode timelock as bip68 sequence
  const sequence = ScriptNum().encode(
    BigInt(bip68.encode({ blocks: timelock }))
  )

  // create unilateral exit path
  const exit = Script.decode([
    sequence,
    'CHECKSEQUENCEVERIFY',
    'DROP',
    myPubKey,
    'CHECKSIG'
  ])
  
  // generate P2TR output key with unspendable key path
  const vtxoTaprootKey = p2tr(
    TAPROOT_UNSPENDABLE_KEY,
    taprootListToTree([forfeit, exit]),
    undefined,
    true
  ).tweakedPubkey

  // combine server pubkey and vtxo taproot key
  const addressData = new Uint8Array(64)
  addressData.set(serverPubKey, 0)
  addressData.set(vtxoTaprootKey, 32)

  return bech32m.encode(
    isTestnet ? 'tark' : 'ark',    // mainnet prefix
    bech32m.toWords(addressData),  // convert to 5-bit words
    1023                           // extends bech32m byte limit
  );
}