unforgeable optical tokens?

[Arnold G. Reinhold]

It might be possible to get the same effect using a conventional 
silicon chip. I have in mind a large analog circuit, something like a 
multi-stage neural network. Random defects would be induced, either 
in the crystal growing process or by exposing the wafer at one or 
more stages with a spray of pellets or chemicals. The effect would be 
to cut wires and alter component values such as resistances,  zener 
diode break down voltages, transistor gains.

Critical parts of the circuit would be protected by a passivation 
layer or would  simply designed with  larger geometries to make them 
less sensitive. Multiple inputs would be driven by D/A converters, 
either in parallel or through a charge coupled analog shift register. 
There would be enough "stuff' in the middle to make it impractical to 
characterize the entire circuit from the inputs. One could use very 
small geometries for the network and still get high circuit yield 
since defects are something we want.

The advantage of this approach over a optical system is that it would 
be very easy to interface with existing technology -- smart cards, RF 
ID, dongles, etc.

Arnold Reinhold



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