Visual Code Authentication Schemes

I bought a new security token and all I got was this lousy phish—
Relay attacks on visual code authentication schemes Graeme Jenkinson, Max Spencer, Chris Warrington, Frank Stajano
{graeme.jenkinson, max.spencer, chris.warrington, frank.stajano}@cl.cam.ac.uk University of Cambridge Computer Laboratory, Cambridge, UK

Abstract. One recent thread of academic and commercial research into web authentication has focused on schemes where users scan a visual code with their smartphone, which is a convenient alternative to passwordbased login. We find that many schemes in the literature (including, previously, our own) are, unfortunately, vulnerable to relay attacks. We explain the inherent reasons for this vulnerability and offer an architectural fix, evaluating its trade-offs and discussing why it has never been proposed by other authors.

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Introduction

We consider a relatively new class of web authentication schemes, currently attracting significant academic and commercial interest, which we refer to as visual code authentication schemes. A user may log into a website which supports such an authentication scheme by scanning a visual code, such as a Quick Response
(QR) code [1], using their hand-held authenticator device, henceforth scanner.
The scanner is generally a smartphone, but might be a dedicated hardware gadget. The user carries their scanner at all times, or at least whenever they might want to authenticate to a website; the scanner may have a mechanism to prevent its misuse if lost or stolen. Our own Pico system [2] is of course in this class too.
Such schemes are interesting because they have some important usability benefits which passwords do not; specifically, there is nothing for users to remember or type1 . Furthermore these schemes are resilient to conventional phishing2 because the long-term secrets never leave the scanner and so an attacker cannot trick the victim into revealing them. However, visual code authentication schemes present a new risk.

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