From Luce Gilmore, Cambridge, UK
Ida Emilie Steinmark reports on efforts to make a physical version of the “one-way functions” of cryptography, in order to detect counterfeits (30 September, p 33). This was, in fact, preceded by a method devised by US and Russian researchers to help verify adherence to agreements in the 1970s Strategic Arms Limitation Talks. It was a tamper-proof seal to prevent covert upgrading of warheads. The procedure was simply to glue the access panels shut with transparent epoxy resin, mixed with a pinch of glitter, in a deliberately messy blob. Once cured, the random pattern was photographed under laser illumination.
It was deemed impossible to upgrade a warhead and then recreate the pattern precisely, positioning each speck of glitter and every lump and ripple of the epoxy mass to nanometre accuracy. I wouldn't like to try it.
