A one time pad would have a finite number of uses available, which could lead to logistical complexity if it was being used as a primary auth mechanism. The ca

A one time pad would have a finite number of uses available, which could lead to logistical complexity if it was being used as a primary auth mechanism. The card actually makes sense, as it amounts to a physical artifact that implements a unique encryption key. If there's enough entropy in generating the card, and the process of using it encodes enough bits of data, it's probably a reasonable solution.