Cryptography Reference
In-Depth Information
Targeted use of public-key cryptography
. Payment cards uses public-key
cryptography precisely when it delivers substantial benefits, namely in
simplified key management for the support of offline data authentication.
Balance of control and flexibility
. PCOs strictly control the part of the key
management infrastructure that they need to, but otherwise devolve control to
participating banks. This provides scalable key management and allows banks
to develop their own relationships with their customers.
Efficient use of related data
. Payment cards use data in a number of imaginative
ways. For example, PANs are used to derive keys, and items of transaction data
are used as challenges in authentication protocols. This is both efficient and
clever.
The next application that we will examine is fundamentally different from
the previous ones. This is the use of cryptography to protect digital video
content that is being broadcast, sometimes referred to as
pay-TV
. What is most
fascinating about this application is that the security service requirements are fairly
straightforward but the key management is very sophisticated. This is because the
environment poses some unusual operational restrictions that require special key
management techniques.
12.5.1
Video broadcasting background
Commercial television broadcasters have traditionally financed the provision
of their services either through government subsidy or advertising revenue.
This is primarily because most analogue broadcast content can be received
by anyone with access to a suitable device, such as a television set. This
makes alternative business models, such as those based on annual subscription,
hard to enforce. For example, enforcement of the annual television license
in the UK involves locating devices and attempting to retrospectively collect
revenue.
An alternative option is to 'encrypt' analogue content using special techniques
that are developed for particular broadcast technologies. This process is often
referred to as
scrambling
. This requires a consumer of content to acquire dedicated
hardware in order to use decryption to recover the content. This requirement thus
presents an opportunity for revenue collection.
Digital video broadcast networks process digital content, thus making it
possible to use the full range of modern cryptographic mechanisms to protect
content. This, in turn, enables a wide variety of different business models. Most
of these require consumers to obtain specific hardware (or occasionally software)
in order to recover content. Common models include
full subscription services
