HardFault from mbedtls_internal_aes_encrypt after porting mqttsn_client_publisher to use Open Thread 1.2

Question

Hello! We are targeting an nrf52840. We were able to compile and successfully use the mqttsn_client_publisher from the latest nRF SDK v4.1.0 for Thread and Zigbee. We then attempted to upgrade to Open Thread 1.2 per these instructions infocenter.nordicsemi.com/index.jsp . Having successfully rebuilt, we loaded the example and now get a HardFault in mbedtls_internal_aes_encrypt shortly after running the application. Exact same call stack and issue as reported here. devzone.nordicsemi.com/.../282556 but unfortunately no resolution was given in that thread. 
 Any help to offer on what might be going on? 
 Thanks, Brad

Jørgen Holmefjord · Accepted Answer

bradastronics said: OK sorry I copied the wrong hash, but it sounds like c6a258e3a5bd90aa26d8245c435c0ae5797027f4 is too old to include OT 1.2. 
 I see. Yes, nRF5 SDK for T&Z v4.1.0 does not support Thread 1.2 features. 
 bradastronics said: As to my OTBR only supporting 1.2 - it is unable to communicate with a 1.1 NCP Thread device flashed from the Nordic example ( nrf52840_xxaa_pca10056.hex) due to missing capabilities in that firmware. I have build my own RCP firmware based on 1.2 and have no issues. I'll have to go copy the error message next week, something about security. 
 I can understand that the OTBR requires some features from Thread 1.2 in the NCP/RCP firmwares used with the border router, but it sounds like you are building a firmware for another node in the network? Will the BR not be able to communicate with other nodes in the network that only supports Thread 1.1?

HardFault from mbedtls_internal_aes_encrypt after porting mqttsn_client_publisher to use Open Thread 1.2

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