Root Certificate Generation for TLS session between microtroller and Azure Edge (in hex)

Sulav Lal Shrestha 361

Hello,

I am able to send telemetry from microcontroller to IOT hub (using legacy iot mqtt client).
I am trying to send the telemetry to IOT edge for which I have generated the root certificate.
I want to use that certificate for establishing TLS session.
The certificate seems to be in DER encoded and in hex format.
However, I am not able to find the encoding for converting DER encoded certificate to hex format.
I have tried Windows-1252,1254,1257 encoding with either CR or LF newline characters.
But, everytime I get parsing error.

Can anyone help me out on this?

I have attached the certificate used for establishing TLS session to communicate with IOT hub.

Thanks,
Sulav

166551-azure-iot-cert.txt

António Sérgio Azevedo 7,666 Reputation points Microsoft Employee

2022-01-20T14:45:09.973+00:00

Hi @Sulav Lal Shrestha are you following the doc here?: Create downstream device certificates

This script command creates several certificate and key files. The following certificate and key pairs needs to be copied over to the downstream IoT device and referenced in the applications that connect to IoT Hub:

<WRKDIR>\certs\iot-device-<device name>-primary-full-chain.cert.pem
<WRKDIR>\certs\iot-device-<device name>-secondary-full-chain.cert.pem
<WRKDIR>\certs\iot-device-<device name>-primary.cert.pem
<WRKDIR>\certs\iot-device-<device name>-secondary.cert.pem
<WRKDIR>\certs\iot-device-<device name>-primary.cert.pfx
<WRKDIR>\certs\iot-device-<device name>-secondary.cert.pfx
<WRKDIR>\private\iot-device-<device name>-primary.key.pem
<WRKDIR>\private\iot-device-<device name>-secondary.key.pem

Thanks!
Sulav Lal Shrestha 361 Reputation points

2022-01-24T19:30:46.82+00:00
I had done that. There were a couple of issues.

I failed to realize that the DER format certificate is already binary encoded. I had written a python script to read the file byte by byte. The tool suggested by @Tiejun Zhou helped.

The buffer size for TLS certificate was not enough for IOT edge TLS certificate. After increasing the buffer size from 4kB to 5kB, the TLS session was established and the messages were sent to IOT edge.

Accepted answer

Tiejun Zhou 1,126 Reputation points Microsoft Employee

2022-01-21T01:16:29.507+00:00
Hi @Sulav Lal Shrestha , you can use xxd command from Linux environment to convert a DER format certificate to hex format C array.

xxd -i <path_to_cert>
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1 person found this answer helpful.
Sulav Lal Shrestha 361 Reputation points

2022-01-24T19:28:09.987+00:00

Thank you, @Tiejun Zhou . I realized later that DER format certificate is binary encoded. I had written a python script to read the file byte by byte and print it out so that I could use it for the C file. This tool helps a lot.
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Root Certificate Generation for TLS session between microtroller and Azure Edge (in hex)

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