On the information-splitting essence of two types of quantum key distribution protocols

With the help of a simple quantum key distribution (QKD) scheme, we discuss the relation between BB84-type protocols and two-step-type ones. It is shown that they have the same essence, that is, information splitting. The choice of an orthogonal carrier or a nonorthogonal carrier, which looks like the main difference between these two types of protocols, is not an important, even not a very explicit matter. This result is instructive for related scheme designing and security analyzing.