Issues With Electronic Machine Readable Travel Documents

Most of us have passports, and most of these passports are by now equipped with chips that store some data, including fingerprints. But six months ago I had no idea how that operates. Now that my country is planning to roll out new identity documents, I had to research the matter.

The chip (which is a smartcard) in the passports has a contactless interface. That means RFID, 13.56 MHz (like NFC). Most typical uses of smartcards require PIN entry from the owner. But the point with eMRTD (Eletronic machine readable travel documents) is different – they have to be read by border control officials anf they have to allow quickly going through Automatic Border Control gates/terminals. Typing a PIN will allegedly slow the process, and besides, not everyone will remember their PIN. So the ICAO had to invent some standard and secure way to allow gates to read the data, but at the same time prevent unauthorized access (e.g. someone “sniffing” around with some device).

And they thought they did. A couple of times. First the mechanism was BAC (Basic Access Control). When you open your passport on the photo page and place it in the e-gate, it reads the machine-readable zone (MRZ) with OCR and gets the passport number, birth date and issue date from there. That combination of those is a key that is used to authenticate to the chip in order to read the data. The security issues with that are obvious, but I will leave the details to be explained by this paper.

Then, they figured, they could improve the previously unsecure e-passports, and they introduced EAC (Extended Access Control). That includes short-lived certificate on the gates, and the chip inside the passport verifies those certificates (card-verifiable certificates). Only then the gate can read the data. You can imagine that requires a big infrastructure – every issuing country has to support a PKI, countries should cross-sign their “document verifier certificates”, and all of those should be in a central repository, where gates pull the certificates from. Additionally, these certificates should be very short-lived in order to reduce the risk of leaking a certificate. Such complexity, of course, asks for trouble. The first version of EAC was susceptible to a number of attacks, so they introduced EACv2. Which mostly covers the attacks on v1, except a few small details: chips must be backward-compatible with BAC (because some gates may not support EAC). Another thing is that since the passport chip has no real clock, it updates the time after successful validation with a gate. But if a passport is not used for some period of time, expired (and possibly leaked) certificates can be used to get the data from the chip anyway. All of the details and issues of EACv1 and EACv2 are explained in this paper.

Since BAC is broken due to the low entropy, SAC (Supplemental Access Control) was created, using the PACE (v2) protocol. It is a password-authenticated key agreement protocol – roughly Diffie-Hellman + mutual authentication. The point is to generate a secret with high entropy based on a small password. The password is either a PIN, or a CAN (Card Authentication Number) printed in the MRZ of the passport. (I think this protocol can be used to secure a regular communication with a contactless reader, if used with a PIN). The algorithm has two implementations GM (General Mapping) and IM (Integrated Mapping). The latter, however, uses a patented Map2Point algorithm, and if it becomes widely adopted, is a bomb waiting to explode.

The whole story above is explained in this document. In addition, there is the BioPACE algorithm which includes biometric validation on the terminal (i.e. putting your finger for unlocking the chip), but (fortunately) that is not adopted anywhere (apart from Spain, afaik).

Overall, after many years and many attempts, the ICAO protocols seem to still have doubtful security. Although much improvement has been made, the original idea of allowing a terminal to read data without requiring action and knowledge from the holder, necessarily leads to security issues. Questions arise about brute-forcing as well – either an attacker can jam the chip with requests, or he can lock it after several unsuccessful attempts.

And if you think passports have issues, let me mention ID cards. Some countries make their ID cards ICAO-compliant in order to allow citizens to use them instead of passports (in the EU, for example, the ID card is a valid travel document). Leaving the question “why would a Schengen citizen even need to go through border control in Europe” aside, there are some more issues: the rare usage of the cards brings the EACv2 vulnerability. The MRZ is visible without the owner having to open it on the photo page – this means anyone who gets a glimpse of the ID card knows your CAN, and then authenticate as if it’s a terminal. And while passports are carried around only when you travel abroad, ID cards are carried at all times, increasing the risks for personal and biometric data leakage many times. Possibly these issues are the reason that by 2014 only Germany and Spain had e-gates that support ID cards as eMRTD. Currently there is the ABC4EU project that is aimed at defining common standards and harmonizing the e-gates infrastructure, so in 5-6 years there may be more e-gates supporting ID cards, and therefore more ID cards conforming to ICAO.

Lukas Grunwald has called all of the above “Security by politics” in his talk at DEF CON last year. He reveals practical issues with the eMRTD, including attacks not only on the chips, but on the infrastructure as well.

Leaking data, including biometric data, to strangers on the metro who happen to have a “listening” device is a huge issue. Stainless steel wallets shielding from radio signals will probably become more common, at least with more technical people. Others may try to microwave their ID cards, like some Germans have done.

It’s not about the automatic control, some say, it’s about the security of the document itself, and by that – the security of everyone. If your fingerprints are signed by your country, surely nobody can create a fake document. First, even when there are checks on the biometrics (photo, iris, fingerprints), they are far from perfect. Also, in order to identify a fake passport, you have to check the fingerprints of everyone. Which they do in the US, but they don’t rely on the ones on the passport – they specifically take your fingerprints when issuing a visa. And reasonably so – in the ICAO system, if the root certificate of any country gets compromised, it can be used to sign fake passports (rogue states aside, are we certain that all countries have proper security around their CA? I’m not). And besides – are fake passports really the threat? Even if passports are ultra-secure (which they aren’t), attackers don’t attack the strongest part of a security system – they attack the weakest part. For example unguarded borders. Arriving by car or bus (where comparing fingerprints is rather impractical). Or, actually, working with people that already have valid passports, like most of the terrorists in recent attacks.

But apparently the “political will” is aimed at ensuring the false sense of security, and at convenience at the airport, allowing for less queues and less human border control officers, while getting all possible data about the citizen. Currently all of that appears to be at the expense of information security, but can it be different? Having an RFID chip in your document is always a risk (banks allow contactless payments up to a given limit, and they accept the risk themselves). But if we eliminate all the data from the passport/ID card, and leave simply a “passport number” to be read, it may be useless to attackers (currently the eMRTD have names, address, birth date, photo, fingerprints).

There is a huge infrastructure already in place, and it operates in batch mode – i.e. rotating certificates on regular intervals. But the current state of technology allows for near-real time querying – e.g. you go the the gate, put your eMRTD, it reads your passport numbers and sends a query to the passport database of the issuing country, which returns the required data as a response. If that is at all needed – the country where you enter can simply store the passport numbers that entered, together with the picture of the citizen, and later obtain the required data in batches. If batches suffice, data on the chip may still be present, but encrypted with the issuer’s public key and sent for decryption. This “issuer database” approach has its own implications – if every visit to a foreign country triggers a check in their national database, that may be used to easily trace citizen’s movements. While national passport databases exist, forming a huge global database is too scary. (Not) logging validation attempts in national databases may be regulated and audited, but that increases the complexity of the whole system. But I think this is the direction this should move to – having only a “key” in the passport, and data in central, (allegedly) protected databases. Note that e-gates normally do picture verification, so that might have to be stored on the passport. (Note: I discovered this proposal for an online verification protocol after writing this post)

Technical issues aside, when getting our passports, and more importantly – our ID cards, we must be allowed to make an informed choice – do we want to bear the security risks for the sake of the convenience of not waiting in queues (although queues form on e-gates as well), or we don’t care about automatic border control and we’d rather keep our personal and biometric data outside the RFID chip. For EU ID cards I would even say the default option must be the latter.

And while I’m not immediately concerned about an Orwellian (super)state tracking all your movements through a mandatory RFID document (or even – implant), not addressing these issues may lead to one some day (or has already lead in less democratic countries that have RFID ID cards), and at the very least – to a lot of fraud. For that reason “security by politics” must be avoided. I just don’t know how. Probably on an EU level?

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