LWM2M System With DTLS

This page describes how to enable DTLS-based LWM2M communication between the gateway and IoT devices in the basic system you’ve already set up.

These instructions assume you are using a BLE Nano 2.

Warning

This is an experimental feature, with important security limitations.

  • The firmware update procedure uses plain HTTP, rather than LWM2M over DTLS. This leaks the contents of the updated firmware binary. (This can be used in denial of service and information disclosure attacks, but the MCUBoot binary will still refuse to boot unsigned binaries.)
  • The Leshan server still allows unauthenticated HTTP access to the IoT devices via its user interface and REST API. For example, this is used below to provision the device token, which leaks it over the local network to any eavesdropper. It also allows interacting with any device objects using an unauthenticated and unencrypted interface.

Generate Credentials Partition

You first need to generate a binary blob containing device credentials to use.

From the ZMP installation directory, run a command like this:

./zephyr-fota-samples/dm-lwm2m/scripts/gen_cred_partition.py --device-id=deadbeef --device-token=000102030405060708090a0b0c0d0e0f --output=cred.bin

The arguments are as follows.

  • --device-id is a public identifier for the device. This is currently limited to eight hexadecimal characters.
  • --device-token is a secret, device-specific token value (i.e., the token must be different for each device on the network). This is a sequence of 32 two-character hexadecimal values, each representing a byte. In the above example, the first byte is 0x00, the second is 0x01, etc.
  • --output is the output file which will contain the binary.

Build and Flash IoT Device With DTLS Enabled

Again from the ZMP installation directory, you now need to re-build and re-flash the application with DTLS enabled, along with the credentials partition:

rm -rf outdir/zephyr-fota-samples/dm-lwm2m/nrf52_blenano2
./zmp build --overlay-config=overlay-dtls.conf zephyr-fota-samples/dm-lwm2m
./zmp flash -b nrf52_blenano2 zephyr-fota-samples/dm-lwm2m
pyocd-flashtool -se -t nrf52 --address 0x7f000 cred.bin

Provision Leshan With Device Token

Now use the Leshan REST API to provision the device ID and token as in the following command line. (Make sure to change each occurrence of deadbeef to your device ID, and the key from 000102...0f to the key value you chose earlier.)

As noted above, this command line uses HTTP, and thus leaks the key, for example to any eavesdropper on the local network:

curl -v -X PUT -H "Content-Type: application/json" -d "{\"endpoint\":\"deadbeef\",\"psk\":{\"identity\":\"deadbeef\",\"key\":\"000102030405060708090a0b0c0d0e0f\"}}" http://localhost:8081/api/security/deadbeef

Use the System

You should now be able to use the system with DTLS enabled in same ways as the basic system.