Cryptography Reference
In-Depth Information
also maintained on the card and is communicated to relying parties during a
transaction.
KEY ESTABLISHMENT
The advantage of a closed system of this type is that the keys stored on a card
can be pre-installed during the manufacturing (or personalisation) process. This
is slightly more complex for RSA key pairs, since they cannot be mass generated
as efficiently as symmetric keys. The session keys used in individual transactions
are established on the fly during the transaction, as just discussed.
A PCO's verification key is installed into terminals during their manufacture.
PCOs also oversee an important symmetric key hierarchy. At the top level are
zone control master keys
, which are manually established using component form
(see Section 10.3.3). These are used to establish the acquirer working keys and
issuer working keys.
KEY STORAGE
All the long-term secret or private keys used in EMV payment card systems are
protected in tamper-resistant hardware, either in the form of an issuer's hardware
security module or the chip on the payment card.
KEY USAGE
In general, key separation is enforced in EMV. The two main security functions
that involve encryption using keys stored on a card are conducted using separate
symmetric keys.
12.4.7
Payment card security issues
APCO's overall security goal is to keep fraud using its cards down to amanageable
level. PCOs such as Visa and MasterCard thus maintain a risk management
division whose function is to assess whether the current security controls are
good enough. The evolution from magnetic stripes to EMV cards also reflects an
adaptation to cope with new perceived threats.
3DSecure is a further response to the growing problems of online fraud. Of
course, 3DSecure is only as secure as the authentication mechanism deployed by
the issuing bank to authenticate its customers. Nonetheless, it seems to offer a
reasonable compromise between security and usability that has helped to reduce
the amount of CNP fraud.
12.4.8
Payment card cryptographic design issues
The main cryptographic design issues concerning payment card cryptographic
security mechanisms are:
Use of well-respected cryptographic algorithms
. Payment cards use 2TDES and
RSA, which are well-established algorithms.
