Monthly Archives: October 2016


Last week I gave a keynote talk at CCS about DigiTally, a project we’ve been working on to extend mobile payments to areas where the network is intermittent, congested or non-existent.

The Bill and Melinda Gates Foundation called for ways to increase the use of mobile payments, which have been transformative in many less developed countries. We did some research and found that network availability and cost were the two main problems. So how could we do phone payments where there’s no network, with a marginal cost of zero? If people had smartphones you could use some combination of NFC, bluetooth and local wifi, but most of the rural poor in Africa and Asia use simple phones without any extra communications modalities, other than those which the users themselves can provide. So how could you enable people to do phone payments by simple user actions? We were inspired by the prepayment electricity meters I helped develop some twenty years ago; meters conforming to this spec are now used in over 100 countries.

We got a small grant from the Gates Foundation to do a prototype and field trial. We designed a system, Digitally, where Alice can pay Bob by exchanging eight-digit MACs that are generated, and verified, by the SIM cards in their phones. For rapid prototyping we used overlay SIMs (which are already being used in a different phone payment system in Africa). The cryptography is described in a paper we gave at the Security Protocols Workshop this spring.

Last month we took the prototype to Strathmore University in Nairobi to do a field trial involving usability studies in their bookshop, coffee shop and cafeteria. The results were very encouraging and I described them in my talk at CCS (slides). There will be a paper on this study in due course. We’re now looking for partners to do deployment at scale, whether in phone payments or in other apps that need to support value transfer in delay-tolerant networks.

There has been press coverage in the New Scientist, Engadget and Impress (original Japanese version).

Security Economics MOOC

In two weeks’ time we’re starting an open course in security economics. I’m teaching this together with Rainer Boehme, Tyler Moore, Michel van Eeten, Carlos Ganan, Sophie van der Zee and David Modic.

Over the past fifteen years, we’ve come to realise that many information security failures arise from poor incentives. If Alice guards a system while Bob pays the cost of failure, things can be expected to go wrong. Security economics is now an important research topic: you can’t design secure systems involving multiple principals if you can’t get the incentives right. And it goes way beyond computer science. Without understanding how incentives play out, you can’t expect to make decent policy on cybercrime, on consumer protection or indeed on protecting critical national infrastructure

We first did the course last year as a paid-for course with EdX. Our agreement with them was that they’d charge for it the first time, to recoup the production costs, and thereafter it would be free.

So here it is as a free course. Spread the word!