I have been covering changes to voting law for over two years now and so far as I know, the Secretary of Homeland Security does not have “the legal authority to create a two-tiered system of voting.” I respect your concerns, but Kobach can’t unilaterally force a new system of voting into place. Bills would have to be introduced and passed in Congress, then signed by the president. (I suspect it might require amending the U.S. Constitution, which is a long and difficult process.) And any such bills would doubtless wind up mired in court challenges for years to come.
This is not to reject your concerns about new limitations to voting rights. There likely are plans afoot in some quarters and new developments should be closely watched. But the idea that the Secretary of Homeland Security can make sweeping changes on his own is false.