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2.2 Attack classes 19
2.2 Attack classes
There are four basic kinds of attacks that can be applied to Rejsekortet, each
representing four different ways of approaching defrauding of the system. They
are as follows:
• Rollback attacks in which the attacker loads back an older state of the
card. This kind of attacks need not much more than the possession of a
card reader to be carried out.
• Attacking the MAC allows forging of valid data to make the system
think it issued it itself. This leads to the attacker being able to add
money, tickets, discount rates, etc. to his/her card. A successful MAC
attack would require the recovery of the key for the DES-MAC used, which
has a complexity of 2 56 .
• Masquerading attacks in which an adversary impersonates another (legitimate)
user of the system.
• Attacks on the infrastructure. These attacks will not be described
in much detail, only possible attack vectors will be set forward. It is
impossible to know how the system works without physical access to the
innards, therefore this kinds of attacks will remain speculative until more
details about the hardware is known.
Another thing that has to be taken into consideration is vandalism. Even though
this kind of attacks does not offer anything to the attacker, it must still be taken
seriously—one cannot leave out the possibility of people deliberately trying to
disrupt the system for fun.
2.3 Analysis of the security
As written in 1.3 Rejsekortet has three lines of defense. The first one is the
use of Mifare Classic itself; the user is not supposed to be reading or writing
to his/her card at all! However, as described in 1.3.1.1 some attacks on Mifare
makes it possible to do just that, making the Rejsekort security depend solely
on the DES-MAC and database sanity checks.
This section will describe some remarks—both positive and negative—to the
security system described in the available documents.