  This paper presents the PUF finite state machine (PUF-FSM) that is served as
a practical {\it controlled} strong PUF. Previous controlled PUF designs have
the difficulties of stabilizing the noisy PUF responses where the error
correction logic is required. In addition, the computed helper data to assist
error correcting, however, leaks information, which poses the controlled PUF
under the threatens of fault attacks or reliability-based attacks. The PUF-FSM
eschews the error correction logic and the computation, storage and loading of
the helper data on-chip by only employing error-free responses judiciously
determined on demand in the absence of an Arbiter PUF with a large CRP space.
In addition, the access to the PUF-FSM is controlled by the trusted entity.
Control in means of i) restricting challenges presented to the PUF and ii)
further preventing repeated response evaluations to gain unreliability
side-channel information are foundations of defensing the most powerful
modeling attacks. The PUF-FSM goes beyond authentications/identifications to
such as key generations and advanced cryptographic applications built upon a
shared key.
