bachelor

1.3 Grades of security 11
contract object, respectively (which can also be assumed to be one per
card.)
These values are probably available to the back-office system.
known that the card transaction number is, see page 52 in [6].
At least it is
1.3 Grades of security
One argument used in the defense of Rejsekortet has been that it implements
several layers of security, and that if one of the layers are broken the other ones
will act redundantly. The layers implemented are the Mifare proprietary crypto,
DES-MAC checksums for the important blocks on the card, and finally a nightly
inspection of the database to determine if users have tried to fool the system in
some way.
1.3.1 Mifare / Crypto-1
Mifare implements a proprietary cryptosystem, Crypto-1, to protect the contents
of the card. The cipher has been proved to be rather weak, and recent
attacks allow an adversary to decrypt and dump the contents of the card in
minutes, see 1.3.1.1.
Crypto-1 is a stream cipher with a key size of 48 bits, but further description is
not in the scope of this thesis. A more detailed description of the cryptosystem
can be found in [2].
1.3.1.1 Mifare insecurities
Because of the market penetration of Mifare it is a very attractive target for
cryptographic attacks. Mifare implements a proprietary cryptosystem called
Crypto-1, which has been proven insufficient by some recent scientific papers.
The most serious attack is presented by Garcia et. al. in a paper called “Wirelessly
Pickpocketing a Mifare Classic Card”[3]. The attack is called the Nested
Authentication attack, and allows an adversary to recover encryption keys for
any sector given the key for just one. This enables an attacker to quickly recover
all keys for a card, given just one. In short, the attack works by being able to