E-Payments: Cardholder Privacy and Non-Repudiation

by David John Boyd

RHUL-MA-2009-25

Abstract:

The development of electronic payment cards has been
evolutionary, of late pushing to protect the card issuers'
financial interests by counteracting an increase in the number
of fraudulent payments made with falsified cards. The
cardholders have a different emphasis: only to be liable for
their own payments and to be able to evidence the payments that
they have or have not made. Card payments tend not to keep the
cardholder's details private, which can facilitate fraud, and
it can be exceedingly difficult for a cardholder to repudiate a
completed payment. This thesis aims to support cardholders by
enhancing their privacy and non-repudiation capabilities.

This thesis is divided into four parts.

The first part looks at how privacy and non-repudiation fit
into the information security hierarchy, and then the
cryptographic mechanisms and algorithms used in this thesis are
described. The widely-used EMV electronic payment card system
is reviewed; followed by card-not-present transactions, which
are particularly problematical.

The main contribution follows where four novel schemes are
proposed that provide enhanced privacy and non-repudiation
services for both card-present and card-not-present payments.
Each of these four categories of payment and security service
requires its own scheme. Privacy is enhanced by stripping out
personally identifiable information and using a different
account number for each transaction. Non-repudiation is
enhanced by leaving an electronic footprint after each
transaction.

Web payments require particular attention. Banks are adept at
authenticating clients. The third part of this thesis brings
together those factors and proposes two further schemes that
provide a single sign-on service to the Web and client
authentication for the Transport Layer Security communications
protocol. The card issuer provides privacy by vouching that it
knows the cardholder and some non-repudiation properties by
maintaining an audit trail.

Finally the thesis concludes and outlines some opportunities
for further research.