Function getConversationKey

src/utils/nip44.ts:36–42

(privateKeyHex: string, publicKeyHex: string)

 * Result is the same regardless of which party computes it: conv(a, B) == conv(b, A)
 */
export function getConversationKey(privateKeyHex: string, publicKeyHex: string): Buffer {
  // ECDH: unhashed 32-byte x coordinate of the shared point
  const shared = secp256k1.getSharedSecret(privateKeyHex, `02${publicKeyHex}`, true)
  const sharedX = Buffer.from(shared).subarray(1) // strip 0x02 prefix

  return hkdfExtract(Buffer.from('nip44-v2'), sharedX)
}

function getMessageKeys(
  conversationKey: Buffer,