Does the security auditor have a point?

On a recent flight, I was sat next to a security auditor. He asked “can someone steal keys used to encrypt credit cards from the server memory?” It depends, was my reply. But his question left me wondering. Why hasn’t anyone built a server side white box implementation?

Why does it depend?
Like any implementation, some are more secure than others. If the server side code was using ‘standard cryptographic APIs’ and they were black box implementations then