The RFID boogeyman, part II: passports

If one could point to a single application responsible for giving RFID its bad reputation, it would have to be passports or machine readable travel documents (MRTD) in the standards parlance. The benefits of using smart card functionality to make passports more difficult to counterfeit are difficult to argue against. On the flip side, it has been equally difficult to articulate the value of having those chips support contactless access over RFID. In the US particularly, it has been a controversial decision pitting the privacy advocacy community against the State Department leading the charge for the new design.

Such vociferous opposition is understandable, as the stakes are  higher compared to use of RFID for payment cards. While it requires something of a  Luddite to completely opt out of the conveniences of credit/debit cards, consumers at least enjoy choice of issuers. The usual market forces are continue to operate: if there is indeed strong reluctance for contactless functionality in payments,  customers will gravitate to banks catering to that demand. (Determined card-holders can even take unilateral action and fry the chip in the card.) By virtue of being government issued, passports offer no such easy opt-out. Crossing national borders usually requires some type of identification, and citizens have little choice but to obtain that ID from their country of their citizenship. More importantly NFC functionality is a critical part of passports– it is not an “optional” feature, unlike credit cards where transactions  can still work the old-fashioned way by swiping the magnetic stripe. (Not to mention that tampering with passports is illegal.) The perception that a privacy infringing technology is being foisted on the populace has fueled many a conspiracy theory and FUD cycles.

That FUD has been non-stop and, quite frequently, wildly inaccurate. One sensationalist article from 2010 claims US passports can be read from 217 feet. Aside from the dubious use of “read” (see earlier post about what it takes to actually recover personal data from a passport) the article also conflates two different technologies. The actual demonstration at BlackHat involved EPC Gen 2 tags, which are RFID tags operating on a different frequency than the NFC chips present in passports. NFC stands for Near Field Communications— emphasis on “near.” While sufficiently powerful transmitters and sensitive antennas will no doubt increase the range significantly, up to several meters, to date there has not been a successful demonstration of reading NFC tags anywhere near distances implied by the article. Granted “attacks always get better” as the saying goes, but the article amounts to arguing that trains are dangerous by citing statistics on horse carriages.

An even more pervasive assumption is that individuals can be tracked simply by virtue of carrying their passport. This is a dubious proposition, at least in the simplistic interpretation of “tracking.” In the manifesto describing seven Laws of Identity— fashionable when  Infocard/CardSpace was all the rage– Cameron posited that the problem with RFID is projecting an omni-directional identity:

Another example involves the proposed usage of RFID technology in passports and student tracking applications. RFID devices currently emit an omni-directional public beacon.

Paraphrased, this is asserting that RFID  tags emit a constant, unique identifier to everyone instead of allowing the owner to project a variable identity based on the observer. While that  holds true for earlier generation of RFID tags, it is demonstrably false for US passports, as anyone can verify with an NFC-capable Android phone. In fact it is required that passports are configured to emit a random identifier, picked anew each time the passport is scanned.

Granted randomizing the identifier emitted at the transport level is a necessary but not sufficient condition to prevent tracking. There could be other constant identifiers lurking in higher level protocols, permitting correlation. Here the picture is more complex. The designers have taken additional steps to avoid obvious pitfalls. For example retrieval of unique chip identifiers (such as the CPLC) is not allowed until the reader is authenticated to the card. That authentication step requires already knowing data from the passport, as explained in previous post. The design translates into a limited tracking capability: at best the reader gets a yes/no answer, learning whether the passport scanned is identical to one where the name, date of birth and expiration are known. By repeating this query, one could check against multiple persons. The time required for issuing these queries increases linearly with each such attempt– and these chips are not exactly blazing fast, given the requirement to be powered by an external field. (There is also an unintentional weakness which permits answering the same yes/no question using only a previously observed exchange with legitimate reader, without knowing the passport data.)

That is still enough for targeted surveillance against a small number of individuals, but not practical for tracking movement of every person with a passport who wanders within range of stealth readers. There is clearly room for improvement, because the expression of user “consent” for getting his/her passport scanned is far from clear. One could imagine alternatives where PIN entry is required (and this PIN can be changed by the user) or even a simple physical switch activated by pressing a touch-sensitive area on the passport. Similar designs have already seen trial deployments for payments. Even better, if NFC convergence takes off and passports are integrated into smart phones some day,  existing mechanisms controlling when NFC functionality is accessible could provide a much better balance of privacy and user control over presenting their identity.


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