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  • Unclonable 'silicon DNA' secures RFID tags

    To counter the counterfeiting of RFID tags by cloning the chips inside them, Verayo's new M4H RFID tags contain ‘silicon DNA’ that identifies them uniquely and makes cloning impossible. All Verayo products are based on a ‘physically unclonable function’ (PUF) in the form of a circuit, which uses random variations in the delays of wires and gates on the chip – the chip's ‘silicon DNA’ – to produce a unique response to a challenge in an authentication session. When the input challenge is presented, a race condition is created in the circuit as two transitions propagate along different paths. An arbiter, implemented as a latch, produces a 1 or a 0 depending on which transition exits first.

    In Verayo's authentication scheme, a 64-bit pulse train challenge is issued to the serial PUF circuit and the chip returns a 64-bit pulse train response that is unique to its manufacturing variations. The challenge/response pair of each chip is unique, so they can be catalogued in a database at the factory and compared with challenge/response pairs generated later during interrogations in the field.

    However, an online database of challenge/response pairs is not a viable solution for the millions of RFID tags used in applications such as mass transit commuter cards. Therefore, Verayo invented its M4H version with an authentication scheme that does not require an online database. The key to offline authentication is DNA readout capability, which identifies the process variations for a particular PUF circuit. Verayo uses the readout capability at the factory to extract the silicon DNA and then disables the readout feature. The extracted silicon DNA is subsequently encrypted and written back to nonvolatile memory in the RFID chip.

    After this, when a reader detects the card it decrypts the PUF circuit's DNA, simulates the circuit in software, and compares the calculated response to the real-time response from a challenge issued to the RFID tag. If the tag's response matches the calculated response, the card is authentic; otherwise it must be counterfeit.

    Elektor has published various articles and projects covering RFID, both pasive and active, UHF and 13.56 MHz. Simply type 'RFID' in the Search box on the home page.

    Image: Verayo

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