Role of Bell-CHSH violation and local filtering in quantum key distribution

In this article, we analyse the relationship between Bell violation and secure key rate of entanglement assisted quantum distribution (QKD) protocols. Specifically, address question whether is necessary or sufficient for communication. We construct a class states which do not show violation, however, can be used communication after local filtering. Similarly, identify another but generating even The existence these two classes demonstrates that as an initial resource neither nor QKD. Our work therefore forces departure from traditional thinking degree brings out role