The MAXREFDES9001 is a complete internet-of-things
(IoT) security reference design featuring a LoRa radio
based, low-power, temperature sensor node secured with
a DS28S60 secure coprocessor, a LoRa gateway, and
a cloud application implemented in AWS infrastructure.
This reference design highlights a robust and easy to
manage end-to-end security scheme with authentication
and confidentiality capabilities independent of the transmission link in use—the LoRaWAN protocol in this case.
The MAXREFDES9001 is designed to easily integrate into
embedded systems enabling confidentiality, authentication, and integrity of information.
The sensor node is motioned by the tiny, low-power,
Cortex-M4-based microcontroller MAX32660 which periodically measures the ambient temperature with the help
of the DS7505, authenticates and encrypts the temperature value using AES-GCM with the DS28S60 secure
coprocessor, and sends it to the AWS infrastructure over
a LoRaWAN network, through a Raspberry Pi-powered
gateway. To prevent rogue nodes from publishing data,
joining the sensor nodes to the network requires a prior
local verification using a convenient NFC-based strong
authentication with the help of the MAX66242 Secure
Authenticator and a dedicated Android application running
on an NFC-enabled Android device.
Once the authentication is successful, proving that the
sensor node is genuine, the Android device communicates
with the cloud application through the Internet to provision
the sensor node; that is, to generate a certificate for the
sensor node and perform an AES-GCM key exchange
between that sensor node and the AWS infrastructure. The
Android device uses the MAX66242 as an NFC bridge to
communicate with the sensor node device’s microcontroller application and store the certificate into the DS28S60
coprocessor, and to have the key exchange done between
the DS28S60 and the cloud application using the Elliptic
Curve Diffie-Hellman (ECDH) protocol. Once the key
exchange is completed, the sensor node is ready to send
its data to the cloud application using the negotiated
AES-GCM key. Further sensor node authentication by
the cloud application is possible using ECDSA since the
sensor node now has a valid certificate with a matching
key pair. Incidentally, the provisioning process also joins
the end device to the LoRaWAN network implemented
using the AWS IoT core, but this is not the main purpose
of the reference design that shows a way to secure data
without relying on the security of the various underlying
communication links.