Seems that "tamper proof" chips, ones that employ complex physical protection which destroys the chip's internal data if disturbed, aren't quite as secure as everyone thinks. Researchers found a way to get the chips to cough up their data, but it's not easy or cheap.
Researchers at the Technical University of Berlin along with Christopher Tarnovsky, VP of Semiconductor Services at a security company out of Seattle, Washington called IO Active, used highly advanced equipment to extract data from a secure chip by turning it over and going in from the back.
They started by using a polishing machine and milled off the back of the chip until it was only about 30 microns thick. Then they put it under a scanning laser microscope fitted with an infrared camera so they could see where operations were being performed by the heat signature. Following this, they used a focused ion-beam lithography device to etch tiny grooves in the chip (about 2 microns deep) to insert probes, so they could essentially sniff out data from the communication channels inside.
While this type of data extraction could only be performed in high-end labs that contain the needed equipment, it represents a proof-of-concept that there is no such thing as a "tamper-proof" chip.