Hello everyone,

I am currently evaluating SSL with a local server and an STM32 device. I'm unable to figure out why the decryption fails with CCM as the cipher suite.

FYI: I am using MbedTLS v2.14.1.

Setup:

I'm using x86 local server with STM32 device as a client.

Here is what happens-

1. Software CCM implementation on the client:

When I use the software implementation of the CCM. Handshake and decryption is successful. Therefore, I can stream the data from STM32 and read it on the local server.

2. Hardware CCM implementation with MBEDTLS_CCM_ALT:

I have used ccm_alt.c provided from STM32Cube v1.9.0. Here, the handshake is successful. But decrypting the message fails.

The errors are:

ssl_decrypt_buf() returned -29056 (-0x7180)

mbedtls_ssl_read_record() returned -29056 (-0x7180)

Checks performed:

Same certificates are used for SW and HW implementations.
CCM self test returns '0' for both HW and SW CCM implementations.
I have reserved enough heap, no memory issues.

Please find all the necessary data in the attachment provided. I have added the logs from the server and the client. I have added the certificates and the code files as well.

It would be of great help if somebody could point at what might be going wrong.

Thank you!

Best regards,

Navin