Reading the US passport with Android– basic access control

Following up on the first part of the post, NFC TagInfo can be used to read the contents of a US passport issued after 2007, after inputting the correct keys. This is done by selecting “Setup keys” option from the menu, then scrolling down to the ePassport/MRTD section. Only three fields are required: the nine-digit passport number, date of birth and expiration date on the passport.

This is part of the basic access control mechanism, intended to limit read access to the document. These three fields can be scanned from the fourth page of the passport, where they are printed in an OCR-friendly font and marked by chevrons. The idea is that access over NFC to the electronically stored data is only possible after having physically scanned one of the interior pages– in other words, no easy pick-pocketing by bumping someone with an NFC reader. (There are several design flaws with BAC, causing it to fall short of that goal, including the predictability of these numbers as well as more subtle cryptographic attacks against the protocol.)

After entering this information, it will be necessary to backtrack and re-scan the passport, as the application will not automatically re-scan with new key set. This time the scan will take a couple of seconds due to the amount of data transferred– the potential maximum 424 Kbps bandwidth for NFC is not even approached doing bulk transfers from the type of chips with limited computing power found in the passports. Afterwards the application will be able to display the encoded data, such as the photograph, as well as additional fields not present in the MRTD data such as issue date and country of birth.



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