Dynamic trust management in computing platforms

A Dynamic Trusted Entity (DTE) 75 utilises a static register 78 and a dynamic register 79 for holding integrity measurements. An integrity measurement stored to the static register is combined with the existing value held in the register, i.e. it is extended, whereas an integrity measurement stored to the dynamic register replaces the previous value held in that register. When a change occurs in a software component 71, e.g. through a software update, the effected part is measured. For a critical change, which is a change to the component that has a potential impact on the ability of the component to implement its intended functionality, the resultant measurement is used to extend the value of the static register, effectively creating a permanent indication that a critical change has taken place; for a non-critical change, the new integrity measurement simply replaces the value held in the dynamic register. The arrangement enables a software component that has only been subject to non-critical changes to be restored to its trustable condition and have this reflected in its integrity metric values (see figure 8).