Two research papers published Monday have finally made it official: The world's most widely deployed radio frequency identification (RFID) smartcard - used to control access to transportation systems, military installations, and other restricted areas - can be cracked in a matter of minutes using inexpensive tools.
One paper - published by researchers from Radboud University in Nijmegen, The Netherlands - describes in detail how to clone cards that use the Mifare Classic. The chip is used widely throughout the world, including in London's Oyster Card, Boston's Charlie Card, and briefly by a new Dutch transit card. Manufacturer NXP and the Dutch government had tried in vain to prevent the researchers from disclosing their findings, arguing that the findings would enable abuse of security systems that rely on the card.
In July, a Dutch judge rejected the request and gave the researchers the green light to publish their paper. It is titled Dismantling MIFARE Classic and was released at the European Symposium on Research in Computer Security (Esorics) 2008 security conference in Malaga, Spain.
It came the same day that Henryk Plötz, a PhD student at Humboldt University in Berlin, published a master thesis (PDF) that includes the full implementation of the algorithm used in the Mifare Classic. The two documents combined mean that virtually anyone with the time and determination can carry out the attacks, said Karsten Nohl, a PhD candidate at the University of Virginia and one of the cryptographers who first warned of the weakness in December.
"Now the weakness that we and others have been talking about for months can be verified independently by really anybody," he said. "The flip side is that everybody can now attack Mifare-based security systems."
Over the past six months, many organizations that rely on the Mifare Classic have upgraded their systems, but Nohl said he is personally aware of a "handful" of systems used by government agencies or large multinational companies that have been unable to make the necessary changes because of the logistical challenges of issuing new badges to employees.
"One hopes that just based on the announcement, most operators of critical security systems have adopted other technologies besides Mifare," Nohl said.
The Achilles Heel in the Mifare Classic is a proprietary encryption scheme dubbed Crypto1. It contains a flaw that causes it to produce outputs that are so cryptographically weak that attackers can guess the key in a matter of minutes. All that's required is an RFID reader, a modest-strength PC, and about 10 minutes. NXP has said it has sold about 2 billion Mifare Classic cards.
The Radboud researchers have already used the discovery to clone Oyster cards and adjust the amount of credit stored on the pre-pay card. Separate students at the Massachusetts Institute of Technology claim to have found gaping holes in the Charlie Card used to collect fares for the Boston subway.
NXP Semiconductor has downplayed the significance of the flaw, saying the card alone should not be relied on for secured access to buildings and other restricted areas. A more robust card made by the company, the Mifare Plus, can use the so-called Advanced Encryption Scheme (AES), a time-tested algorithm that is widely believed to be secure. ®