code: def verify_hmac(self, data):
          
          hmac = HMAC(self.SK_ar, digestmod=sha256)
          hmac_theirs = data[-MACLEN:]
          hmac.update(data[:-MACLEN])
          hmac_ours = hmac.digest()[:MACLEN]
          logger.debug('HMAC verify (ours){} (theirs){}'.format(
              binascii.hexlify(hmac_ours), binascii.hexlify(hmac_theirs)))
          if hmac_ours != hmac_theirs:
              raise IkeError('HMAC verify failed')
docs: Verifies the HMAC signature of an encrypted (SK, 46) payload using self.SK_ar
  
          :param data: bytes(payloads.SK())
          :raise IkeError: if calculated signature does not match the one in the payload