  Security graphs model attacks, defenses, mitigations, and vulnerabilities on
computer networks and systems. With proper attributes, they provide security
metrics using standard graph algorithms. A hyperflow graph is a
register-transfer level (RTL) hardware security graph that facilitates security
verification. A hyperflow graph models information flows and is annotated with
attributes that allow security metrics to measure flow paths, flow conditions,
and flow rates. Hyperflow graphs enable the understanding of hardware
vulnerabilities related to confidentiality, integrity, and availability, as
shown on the OpenTitan hardware root of trust under several threat models.
