Today's computing systems are highly vulnerable to attacks, in large part because nearly all computers are part of a hardware and software monoculture of machines in its market, industry or sector. This is of special concern in mission-critical networked systems upon which our civil, industrial, and defense infrastructures increasingly rely. One approach to tackle this challenge is to endow these systems with dynamic computational diversity, wherein each processor assumes a sequence of unique variants, such that it executes only machine code encoded for a variant during the time interval of that variant's existence. The variants are drawn from a very large set, all adhering to a computational diversity architecture, which is based on an underlying instruction set architecture. Thus any population of machines belonging to a specific diversity architecture consists of a temporally dynamic set of essentially-unique variants. However, an underlying ISA enables development of a common development toolchain for the diversity architecture. Our approach is hardware-centric, relying on the rapidly developing microelectronics technologies of ternary computing, resistive RAM (ReRAM) memory, and physical unclonable functions. This paper describes our on-going work in dynamic computational diversity, which targets the principled design of a secure processor for embedded applications.