I am working on a project using the STM32F207ZG (NUCLEO-F207ZG) microcontroller with FreeRTOS, LwIP (Ethernet), and wolfSSL to communicate securely with cloud servers over HTTPS. I am able to successfully perform a TLS handshake and communicate with an AWS server by loading the Amazon Root CA 1 certificate—everything works as expected in this case. However, when I attempt to connect to a Firebase server using the corresponding root certificate, the TLS handshake fails with error code -188, which corresponds to ASN_NO_SIGNER_E. I verified that the Firebase root certificate is valid by testing it with the wolfSSL example code on a PC, where it worked correctly, indicating the certificate itself is not the issue. I also encountered the same -188 error when trying to connect to an Azure server, again using the appropriate root certificate. This suggests the problem is specific to the STM32 + wolfSSL embedded environment. Since AWS, Firebase, and Azure all use similar TLS configurations and I am using the same STM32 firmware setup in each case, I am trying to understand why only the Firebase and Azure connections fail. I would greatly appreciate any insights or suggestions on whether this issue could be related to SNI support, certificate parsing limitations, cipher suite compatibility, or other wolfSSL or STM32-related configuration constraints.
