Waving a Smart card in front of a radio frequency identification (RFID) reader can provide access to buildings, pay for subway rides, and even initiate credit-card transactions. With more than a billion units sold, the NXP Mifare Classic RFID tag is the most commonly used smart-card chip; it can be found in the London subway system's Oyster card, Australia's SmartRider, and the Boston subway's ­Charlie Card. Security researcher Karsten Nohl, who recently got his PhD in computer science from the University of Virginia, and ­"Starbug," a member of a Berlin hacker group called the Chaos Computer Club, hacked into a Mifare Classic's hardware to gain insight into its cryptographic algorithms. After analyzing the chip, Nohl questioned its security in a series of presentations at recent conferences, including Black Hat in Las Vegas.

An Acetone Bath
Melting a smart card with acetone reveals an RFID chip within (visible in the lower right at the end of the video). The process takes about a half hour. After extracting the chip, a hacker can process it further to analyze its construction and programming.

RFID Chip
Nohl and Starbug used acetone to peel the plastic off the card's millimeter-square chip. Once they isolated the chip, they embedded it in a block of plastic and sanded it down layer by layer to examine its construction. Nohl compares this to looking at the structure of a building floor by floor.