[iybffwsz] Slicing internal structure

Take a material with random internal structure and slice it.  The two halves form a difficult-to-forge pair that matches in 2D at the formerly internal boundary.

A sentimental pair of jewelry for two people.

Symmetric cryptographic key distribution.

There is a practical problem of verifying a match.  Easier is comparing 1D patterns, like grain of wood across a sliced plank.