Thursday 13 September 2012

Severe Security Flaw in ATMs

Ross Anderson has published a severe security flaw in some ATM machines. The nonce sent from the ATM to the card in the process of authenticating the card is predictable. Therefor, an attacker can do the following: First, identify a vulnerable ATM and predict such a nonce. Second, send the nonce to the card of the victim using a fake POS terminal. Record the authentication answer from the card. Program a chip card with that answer. Third, replay that answer to the vulnerable ATM.
All kinds of details are given in the linked publication. It seems that this vulnerability has already been used in real frauds.
Such severe implementation issues cast big doubts on the whole EMV scheme. This could only happen because the certification process for the ATMs did not ensure the unpredictability of the nonces, where the security of the protocol depends on this unpredictability.