summary.tex~

\chapter{Summary}
This bachelor's thesis is completed in spring 2010, and deals with the new Danish ticketing system called Rejsekortet, which is expected to be in nationwide production in metros, busses and trains sometime in 2012. The system is designed to completely replace paper tickets with the reasoning that it will become easier to administer fare prices, as well as being able to set forth very precise models for the traffic flow, which in turn will be able to aid in possible reorganization of the public transit net.

Rejsekortet is designed to function offline, which entails that data such as the card balance and active tickets are stored on the card. To prevent card-based fraud, a series of security mechanisms has been set in place, each providing to a layered security model.  One of these mechanisms is the card itself, which from the factory has a cryptographic mechanism securing against unauthorized reading or writing to the card. Another mechanism is a recognized authenticity verification algorithm, put in place to ensure overall safety of the card in case the card is compromised. The third layer is a nightly run-thorough of the transaction database, in order to prevent cards being copied, etc.

The thesis presents an attack on one of these security measures, namely a \emph{time-memory trade-off} that allows recovery of a secret key for the aforementioned authentication algorithm that is executed during Rejsekort transactions. In addition, the thesis presents an analysis of possible exploitation opportunities if the key for the authenticity check becomes publicly known.