Hardware trust implications of 3-D integration

3-D circuit-level integration is a chip fabrication technique in which two or more dies are stacked and combined into a single circuit through the use of vertical electroconductive posts. Since the dies may be manufactured separately, 3-D circuit integration offers the option of enhancing a commodity processor with a variety of security functions. This paper examines the 3-D design approach and provides an analysis concluding that the commodity die system need not be independently trustworthy for the system of joined dies to provide certain trustworthy functions. In addition to describing the range of possible security enhancements (such as cryptographic services), we describe the ways in which multiple-die subsystems can depend on each other, and a set of processing abstractions and general design constraints with examples to address these dependencies.