Check ota firmware signature with rsa 2048 base64 public key.

[mrdebug]

Hi, before to use a new firmware I have to store it in the spiffs partition and check the signature using a rsa 2048 public key.
The public key isn't in pem format it is in base64 format.
Has anyone got an example on how to check the signature of a file or a stream in esp32, using a base64, public key?