A high-speed pre-production superscalar microprocessor that 'works encrypted' is described here. Data in registers, on buses, and (in consequence) in memory, is kept in encrypted form. It is intended to protect user data being processed remotely or overseen by untrusted operators.
Breuer, P. T., & Bowen, J. P. (2016). A Fully Encrypted Microprocessor: The Secret Computer is Nearly Here. In Procedia Computer Science (Vol. 83, pp. 1282–1287). Elsevier. https://doi.org/10.1016/j.procs.2016.04.267