Cryptography Reference
In-Depth Information
12.5.5
Video broadcast security issues
Digital video broadcast schemes appear to have the capability of providing strong
protection for broadcast content. This is extremely important for the broadcast
providers, since they rely on encryption to protect their source of revenue. The
protection of the content ultimately relies on the security of CSA, which despite
some concerns remains fairly well regarded. Although the key length is short by
modern standards, the keys are frequently changed. The security of these keys also
relies on the encryption algorithms and key management techniques deployed by
a specific broadcast provider to protect all the keys in the key hierarchy.
12.5.6
Video broadcast design issues
Video broadcast networks have provided us with a very interesting application of
cryptography, with the following design issues:
Use of symmetric cryptography
. The closed nature of a video broadcast scheme
facilitates the use of a fully symmetric cryptosystem.
Use of a symmetric key hierarchy
. Video broadcast schemes provide a good
example of the benefits of deploying a key hierarchy to support symmetric key
management.
The influence of operational constraints
. While the security requirements for
video broadcast networks are fairly straightforward, the operational constraints
require some innovative key management controls. Of particular interest are
the techniques used in order to provide instant and synchronised access to
broadcast content across a potentially large consumer base.
Partially standardised infrastructure
. Video broadcast schemes follow some
common standards, for example, for content encryption, while leaving other
aspects such as higher-level key establishment open to custom design by
individual broadcast providers. While this provides the opportunity for a
diverse market of interoperable schemes, it also presents a potential source
of vulnerability in specific systems.
Note that the security of video broadcast networks is just one example of a larger
set of applications relating to the wider problem of
digital rights management
,
which concerns technologies for limiting the access of users to digital content.
The applications that we have looked at so far have all had fairly specific goals, and
hence well-defined specific security requirements. Our next use of cryptography
is quite different in this regard. National (citizen) identity cards are normally
