Improving the Security of EMV Contactless Payments
Student : Martin Emms – Supervisor : Aad Van Moorsel
School of Computing Science
Aims
Protocol Analysis
In order to improve security of EMV contactless payments
protocol, we must first meticulously analyse the current
protocol and identify any potential vulnerabilities. To perform
the analysis we have created an emulation of an EMV contactless
Point of Sale (POS) terminal. The POS emulator aims to
precisely implement the EMV contactless protocol. To prove
that any security flaws that we find are “real” we must be able
to show that the emulator is a true representation of the EMV
specification.
Our analysis of the EMV protocol is guided by the application of
this methodology. The feedback loops add significant detail to
our analysis of the EMV protocol and have allowed us to build a
list of anomalies identified in the protocol.
From the identified anomalies we build test cases. The
emulator code is used run the test cases against real credit /
debit cards.
Methodology
We have employed a systematic methodology to implement the
POS emulator. The key to our approach is to provide a
documented linkage between EMV specification(s) and the
resultant POS emulator code.
UML diagrams are used to provide a concise overview of each of
the five EMV transaction protocol sequences. The UML diagrams
are linked to the EMV specification documents with descriptive
text for each protocol step which contains a list of references to
the EMV specifications.
The emulator code is linked to the EMV specification using the
same descriptive text and list of references that were provided
with the UML diagrams.
The diagram illustrates our methodology. The feedback loops
provide the mechanism by which we refine (and document) our
understanding of the EMV specification. The emulator code is
derived from the UML diagrams, descriptive text and EMV
references.
Results
The anomalies we have identified reside in areas of the EMV
protocol specification(s) where the specification is unclear or
contradictory.
Contactless Verify PIN – Contactless transactions do not
require a PIN to be entered. A large number of cards in
circulation in the UK allow contactless access to the secure
functionality of Verify PIN which compromises their security by
allowing an attacker to probe for their PIN number without the
cardholders knowledge.
Currency Limits Conversion – EMV transactions can be
approved quickly offline by the card for low value transactions
or less quickly online by the bank for higher value transactions.
The card will decide to force the transaction online if the value
is above the card’s transaction limits. However the EMV
specification does not clearly specify what the card should do
in the case of foreign currency transactions. Testing shows that
the cards will approve offline transactions of any value in
another currency (for instance €5,000,000).
Cardholder Verification Method (CVM) – EMV cards contain the
CVM field which specifies the method that should be used to
identify the cardholder as the valid cardholder (i.e. PIN,
signature or for contactless no validation of cardholder). Our
testing shows that the cards accept the POS terminal’s choice
of verification method even when that contradicts the rules
encoded into the CVM
Conclusion
The purpose of the emulator is assist us in our analysis of the
security of the existing EMV protocol to discover any potential
weaknesses / anomalies. Once anomalies are discovered the
emulator can assist us in developing and testing practical
solutions.
It is therefore vital that we ensure a rigorous but practicable
design and implementation process in the development of the
emulator software. At the centre of the process is the
identification of a set of UML sequence diagrams and the
associated EMV reference lists that precisely capture the EMV
transaction protocol sequences.
Feedback from the insights gained in coding the emulator and
the insights from assisting to creating the abstract model are
used to ensure the quality and accuracy of the EMV emulator.