3.8 Secure coprocessors

In parallel to the development of trusted computing technologies described above, numerous alternative architectures, whose aim is also to develop a more secure and trustworthy platform, have been developed.

The most familiar of these alternative architecture types involves platforms which contain secure coprocessors. A secure coprocessor provides a tamper-resistant computing environment in which functions may be executed without interference, despite physical or logical access to the device. The IBM 4758 is an example of a user configurable, tamper-resistant coprocessor with the following properties ^[33]:

• A hardware tamper response;

• RNG;

• A layered design, where each device should have at least two layers, one responsible for implementing the code load security policy, which should be validated as correct, and a subsequent layer or layers for device personalisation;

• Self-initialisation, which implies that a programmable device must leave the factory ready to respond to tampering;

• Outbound authentication, which allows external entities to determine the exact applications running on the device;

• General coprocessor and auxiliary processors, which, for example, allow the efficient implementation of DES and modular arithmetic;

• Persistent storage, which may protect application data or arbitrary data directly using the 4758 tamper response in battery backed RAM, or indirectly by encrypting the data using keys stored in battery backed RAM; and also

• A third party programmable interface, which is as useable as possible.

Coprocessors essentially provide a tamper-resistant secluded area on a platform in which particular applications may be securely executed. As highlighted above, a variety of security services may...