In their Black Hat stage performance, employees of a security company showed how apps on certain mobile phones can access fingerprint data if the phone has a fingerprint sensor. The usual discussions ensued about rotating your fingerprints, biometrics being a bad idea, and biometric features being usernames rather than passwords. But was there a problem in the first place? Let’s start from scratch, slightly simplified:
- Authentication is about claims and the conditions under which one would believe certain claims.
- We need authentication when an adversary might profit from lying to us.
- Example: We’d need to authenticate banknotes (= pieces of printed paper issued by or on behalf of a particular entity, usually a national or central bank) because adversaries might profit from making us believe a printed piece of paper is a banknote when it really isn’t.
- Authentication per se has nothing to do with confidentiality and secrets, as the banknotes example demonstrates. All features that we might use to authenticate a banknote are public.
- What really matters is effort to counterfeit. The harder a feature or set of features is to reproduce for an adversary, the stronger it authenticates whatever it belongs to.
- Secrets, such as passwords, are only surrogates for genuine authenticating features. They remain bound to an entity only for as long as any adversary remains uncertain about their choice from a vast space of possible values.
- Fingerprints are neither usernames nor passwords. They are (sets of) biometric features. Your fingerprints are as public as the features of a banknote.
- We authenticate others by sets of biometric features every day, recognizing colleagues, friends, neigbours, and spouses by their voices, faces, ways of moving, and so on.
- We use even weaker (= easier to counterfeit) features to authenticate, for example, police officers. If someone is wearing a police uniform and driving a car with blinkenlights on its roof, we’ll treat this person as a police officer.
- As a side condition for successful attack, the adversary must not only be able to counterfeit authenticating features, the adversary must also go through an actual authentication process.
- Stolen (or guessed) passwords are so easy to exploit on the Internet because the Internet does little to constrain their abuse.
- Attacks against geographically dispersed fingerprint sensors do not scale in the same way as Internet attacks.
Conclusion: Not every combination of patterns-we-saw-in-security-problems makes a security problem. We are leaving fingerprints on everything we touch, they never were and never will be confidential.
We just finished reviewing the final, ready-to-print version of our article Electronic Identity Cards for User Authentication—Promise and Practice, which will appear in the upcoming issue of IEEE Security & Privacy Magazine (vol. 10, no. 1, jan/feb 2012, DOI: 10.1109/MSP.2011.148). We outline how the German eID system works and discuss application issues. Here is our abstract:
Electronic identity (eID) cards promise to supply a universal, nation-wide mechanism for user authentication. Most European countries have started to deploy eID for government and private sector applications. Are government-issued electronic ID cards the proper way to authenticate users of online services? We use the German eID project as a showcase to discuss eID from an application perspective. The new German ID card has interesting design features: it is contactless, it aims to protect people’s privacy to the extent possible, and it supports cryptographically strong mutual authentication between users and services. Privacy features include support for pseudonymous authentication and per-service controlled access to individual data items. The article discusses key concepts, the eID infrastructure, observed and expected problems, and open questions. The core technology seems ready for prime time and government projects deploy it to the masses. But application issues may hamper eID adoption for online applications.
We think that eID functions of government-issued ID cards will not replace means of everyday online authentication. With eID, there will be few new use cases for ID cards, eID just supports online versions of the traditional use cases. Most of the traditional use cases in Germany involve bureaucracy or legal requirements: legal protection for children and young persons, required identification of mobile phone users or bank account holders, or procedures of administrative bodies involving »Ausweis bitte!« at some point. For those who followed the debate and rollout in Germany, there should be nothing new in our article, but the article may come in handy as a reference for international audiences.
Our article will be in good company as it will appear in a theme issue on authentication. If I read the preprints collection correctly, there will be a user study by Amir Herzberg and Ronen Margulies, Training Johnny to Authenticate (Safely), and an article by Cormac Herley and Paul van Oorschot, A Research Agenda Acknowledging the Persistence of Passwords (authors’ version). It seems sexy to many to call the days of the password counted—IBM just predicted password authentication would die out soon—but if I had to make a bet I would follow Cormac and Paul.
The final version of our article will be paywalled by IEEE, but you can find our preprint with essentially the same contents on our website.