Function deriveAddress

src/services/x402/config.ts:38–79

* Derives an Ethereum address from a private key using secp256k1. * Uses Node.js native crypto for the EC operation.

(privateKeyHex: string)

 * Uses Node.js native crypto for the EC operation.
 */
function deriveAddress(privateKeyHex: string): string {
  const { createPublicKey, createPrivateKey } =
    require('crypto') as typeof import('crypto')

  const keyHex = privateKeyHex.startsWith('0x')
    ? privateKeyHex.slice(2)
    : privateKeyHex
  const keyBuffer = Buffer.from(keyHex, 'hex')

  // Create an EC private key in DER format for secp256k1
  // DER prefix for secp256k1 private key (RFC 5915)
  const derPrefix = Buffer.from(
    '30740201010420',
    'hex',
  )
  const derMiddle = Buffer.from(
    'a00706052b8104000aa144034200',
    'hex',
  )

  const privateKey = createPrivateKey({
    key: Buffer.concat([derPrefix, keyBuffer, derMiddle]),
    format: 'der',
    type: 'sec1',
  })

  const publicKey = createPublicKey(privateKey)
  const pubKeyDer = publicKey.export({ type: 'spki', format: 'der' })

  // Extract the 65-byte uncompressed public key (last 65 bytes of SPKI DER)
  const uncompressedPubKey = pubKeyDer.subarray(pubKeyDer.length - 65)

  // Ethereum address = last 20 bytes of keccak256(pubkey[1:])
  // pubkey[0] is 0x04 prefix for uncompressed key
  const { createHash } = require('crypto') as typeof import('crypto')
  const hash = createHash('sha3-256')
    .update(uncompressedPubKey.subarray(1))
    .digest()
  const rawAddress = '0x' + hash.subarray(hash.length - 20).toString('hex')

  return toChecksumAddress(rawAddress)
}

/** Retrieves x402 config from global config */
export function getX402Config(): X402WalletConfig {