The U.S. government is “taking a very serious look” at improving privacy protection for the new wireless-readable passports, according to an official quoted in a great article by Kim Zetter at Wired News. Many people, including me, have worried about the privacy implications of having passports that are readable at a distance.
The previously proposed system would transmit all of the information stored on the inside cover of the passport – name, date and place of birth, (digitzed) photo, etc. – to any device that is close enough to beam a signal to the passport and receive the passport’s return signal.
The improved system, which is called “Basic Access Control” in the specification, would use a cryptographic protocol between the passport and a reader device. The protocol would require the reader device to prove that it knew the contents of the machine-readable text on the inside cover of the passport (the bottom two lines of textish stuff on a U.S. passport), before the passport would release any information. The released information would also be encrypted so that an eavesdropper could not capture it.
I have not done a detailed security analysis of the crypto protocols, so I can’t vouch for their security. Juels, Molnar, and Wagner point out some protocol flaws (in the Basic Access Control protocol) that are probably not a big deal in practice. I’ll assume here that the protocols are secure enough.
The point of these protocols is to release the digital information only to an entity that can prove it already has had access to information on the inside of the passport. Since the information stored digitally is already visible (in analog form, at least) to somebody who has that access, the privacy risk is vastly reduced, and it becomes impossible for a stranger to read your passport without your knowledge.
You might ask what is the point of storing the information digitally when it can be read digitally only by somebody who has access to the same information in analog form. There are two answers. First, the digital form can be harder to forge, because the digital information can be digitally signed by the issuing government. Assuming the digital signature scheme is secure, this makes it impossible to modify the information in a passport or to replace the photo, steps which apparently aren’t too difficult with paper-only passports. (It’s still possible to copy a passport despite the digital signature, but that seems like a lesser problem than passport modification.) Second, the digital form is more susceptible to electronic record-keeping and lookup in databases, which serves various governmental purposes, either legitimate or (for some governments) nefarious.
The cryptographic protocols now being considered were part of the digital-passport standard already, as an optional feature that each country could choose to adopt or not. The U.S. had previously chosen not to adopt it, but is now thinking about reversing that decision. It’s good to see the government taking the passport privacy issue seriously.
