  This paper studies how to implement a privacy friendly form of ticketing for
public transport in practice. The protocols described are inspired by current
(privacy invasive) public transport ticketing systems used around the world.
The first protocol emulates paper based tickets. The second protocol implements
a pay-as-you-go approach, with fares determined when users check-in and
check-out. Both protocols assume the use of a smart phone as the main user
device to store tickets or travel credit. We see this research as a step
towards investigating how to design commonly used infrastructure in a privacy
friendly manner in practice, paying particular attention to how to deal with
failures.
