Helmi sat at their workbench, staring at a stack of identical gift tags waiting to be attached to Santa’s presents. Each tag needed to serve as a certificate of authenticity—a magical guarantee that the gift was truly from Santa himself. But in a world of clever copycats, these tags had to be unclonable, unique for every present. Digital solutions had been proposed, but Helmi scoffed at the complexity and energy waste of cryptographic signatures. “We need something simpler, something analog,” they mused.

The answer was in physically unclonable functions (PUFs), which used the inherent randomness of physical materials to create unique identifiers. Helmi grabbed a handful of snowflake-patterned tags, each embedded with tiny, irregular imperfections in its design. By passing light or a tiny electric current through these imperfections, each tag produced a unique analog signature—impossible to replicate, even with the best technology.

Helmi tested the system, attaching a tag to a toy train and running it through Santa’s scanner. The sleigh dashboard lit up: Verified—Santa’s Workshop, North Pole. Helmi grinned, satisfied. “Unclonable, energy-efficient, and magical. These tags are more than certificates—they’re part of the magic of Christmas itself.”