Hi Oytis,

Thank you for reaching out with your question. As noted in the comment the valid use case for the callback function that can always return success is when you are using a Hardware Security Module to check the signature for you (ATECC508A/608A, ST Safe, etc). There is no need to check the signature twice, that just wastes computation cycles that could be spend on more interesting tasks.

The valid use case for checking the signature that was generated is if you wish to ensure the signature is valid before sending it. Imagine you have a backend system that can crank out thousands of signatures but you're sending those signatures to embedded systems that take on the order of 10's or 100's of seconds to perform a verify operation. You can save some time by checking the signatures are correct on the backend before shipping them to the field devices rather then sending a bad one, having the field device fail, and then sending another. Our library is designed with embedded systems in mind and we provide some unique functionality for those of our users that have requested it.

Please let us know if you have any other questions!

Warm Regards,

KH