3.5.4 Reconstruct Operation

The Reconstruct operation is the same as the Start operation, except that Reconstruct does not include the Anti-aging phase. This operation can be used instead of a Start operation in the following cases only:
  • The PUF SRAM is powered off most of the time
  • The time from power-on or reset to key operations is time-critical

In other cases, the Start operation must be used.

Important: If the Reconstruct operation is used and the device’s PUF SRAM remains powered on for a long time, Stop and Start operations must be launched as soon as possible after the time-critical part of the application has been completed. This applies the Anti-aging procedure and improves the long-term reliability of the PUF module.

During the Reconstruct operation, the SRAM start-up values and the activation code that were generated during enrollment are used to reconstruct the intrinsic PUF key. When the activation code of another device is used, the reconstruction will fail and the PUF module will respond with an error indication.

After successful completion of the Reconstruct operation, diagnostic information about the PUF quality is provided in the PUF score (see PUF Diagnostics for details).

Note: The PUF scores returned after a Reconstruct (or Start) operation and Enroll (or Test PUF) operation can differ because these operations measure PUF quality in different ways.