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Security researchers have discovered a technique for reliably detecting the presence and nationality of a nearby e-passport.

Most newly issued passports carry an embedded RFID containing digitally signed biometric information. Access to this chip is wireless, which introduces a security risk, the possibility that an attacker might be able to access data on a person’s passport without the owner knowing.

To frustrate wireless reading of passport content without an owner’s consent, e-passports use a mechanism called Basic Access Control (BAC). The approach means that in order to read data from the RFID chip you need to optically read a key, printed in passports. This key is based on a passport serial number. Subsequent communication between a passport and a reader is then encrypted to prevent eavesdropping. All EU passports implement BAC.

Weaknesses in the encryption mechanism used in BAC in withstanding brute force attacks have already been reported.

The latest research uncovers a different shortcoming - the possibility that thieves could use technology to detect the presence and nationality of passports in a crowd, the sort of information that might be useful for a hi-tech pickpocket.

"This turns out to be surprisingly easy to do," the researchers report. "Although passports implement the same standard, there are differences that can be detected, especially by sending ill-formed requests, before Basic Access Control takes places."

The attack works because ICAO (International Civil Aviation Organization) specs do not prescribe a standard response to particular malformed requests, leaving room for diversity among implementations. If the ICAO specs did require a standard response for commands not listed in the specs and all malformed requests, this would make distinguishing passport nationalities much harder or even impossible, the researchers note.

Using this scanning approach the team was able to reliably detect the nationality of passports from 10 different countries: Australia, Belgium, France, Germany, Greece, Italy, the Netherlands, Poland, Spain, and Sweden. E-passports from other countries implementing BAC might also be vulnerable.

Eavesdropping on e-passports has been shown to be possible from up to nine meters for passive eavesdropping. Scanning passports involves generating a stronger magnetic field, creating practical problems for would-be thieves. Even so previous researcher suggests a device capable of scanning up to 25cm can be made for around $100.

The researchers - Wojciech Mostowski and Erik Poll, both from Radboud University, and Henning Richter of Lausitz University - argue their findings strengthen the case for metal shielding to prevent communication between a reader and a passport while the identity document is closed. This safeguard is already used in US passports as an alternative to Basic Access Control.

"While not an immediate security threat to the passport itself, it could be a concern to the passport holder," the researchers note. "This functionality is clearly useful for passport thieves."

The researchers also document other approaches to fingerprinting e-passports. Any research documenting cryptographic shortcomings is interesting but we can't help thinking that, in practice, would-be passport thieves would find it easier simply to hang around airports and wait for arrivals from a country whose passports they are interested in nicking. Alternatively they might hang around downtown airport shuttle terminals and take their chances there.

The researchers paper can be found here (PDF). ®

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