Computer Laboratory

DigiTally

DigiTally is an overlay payment scheme for use on mobile phones, whose goals are to extend mobile phone payments to areas with poor connectivity and reduce transaction fees. DigiTally enables two people to do a payment transaction by simply copying short strings of numbers between their phones. This doesn't need either smartphones or a network connection. Either phone can upload the transaction later, once it gets a network connection.

Overview

DigiTally phones

Mobile payments are available in many less developed countries. There are over 200 operators worldwide, and mobile payments have been transformative in as many as 20 such countries. They can support local payments, migrant remittances, and other financial services such as microcredit, savings, and access to government welfare and subsidies.

The Bill & Melinda Gates Foundation called for proposals for a means of extending mobile payments to people living in areas with poor or no network service. We now have a model, called DigiTally, that enables two people to do a payment transaction by simply copying short strings of numbers between their phones. This doesn't need either smartphones or a network connection. Either phone can upload the transaction later, once it gets a network connection.

The goal of the project is to develop and test a mobile electronic purse system, whose design and implementation will be put in the public domain, so that anyone can use it. The idea is to extend phone payment systems so that people can make payments in areas that have no network, or where service is intermittent or congested. It can also enable payment service providers who are not phone companies and who therefore face nonzero marginal network costs to cut these costs by making small or repeat transactions on a store-and-forward basis.

We collaborated with researchers from Strathmore University (Nairobi, Kenya), and I made the trip to evaluate the prototype and visit rural areas of Kenya in August-September 2016. Our paper summarising the results of a pilot study was accepted to the Symposium on Usable Privacy and Security (SOUPS), the leading security usability event, which I presented at SOUPS 2017 in Santa Clara, California in July 2017.

More information is available at our Security Group's blog.

Resources

Documents

  • Slide deck: DigiTally slides
  • SMAPs: Short Message Authentication Protocols (International Workshop on Security Protocols 2016, SPW24) [PDF]
  • SMAPs: Short Message Authentication Protocols (Transcript of discussion) [PDF]
  • DigiTally: Piloting Offline Payments for Phones (13th Symposium on Usable Privacy and Security, SOUPS 2017) [PDF] [Slides] [Blog]
  • Can we redesign mobile payments to deal with poor networks and cut transaction fees? public lecture given with Ross Anderson at Strathmore University (Nairobi, Kenya), 29 August 2016. [Slides]
  • CCS 2016 Keynote by Ross Anderson: Is it practical to build a truly distributed payment system?, 23rd ACM Conference on Computer and Communications Security, Hofburg Palace, Vienna, Austria, 26 October, 2016. [CCS 2016 keynote slides]

Videos

  • CCS 2016 Keynote by Ross Anderson: Is it practical to build a truly distributed payment system?, 23rd ACM Conference on Computer and Communications Security, Hofburg Palace, Vienna, Austria, 26 October, 2016. [CCS 2016 keynote Youtube video]
  • Main model video on feature (basic) phones: DigiTally (Note: this video is about 214 MB)
  • Model video on iPhones (screen grab): DigiTally on iPhones

Media coverage

New Scientist, Engadget, PC watch, Payment week, NFC world.

Acknowledgment

This project is supported by a grant from the Bill & Melinda Gates Foundation.

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