An integrated circuit assembly having monitoring circuitry for observing the internal signals of the system so that its properties are captured. The system properties are manipulated so that they can be used as a pseudo random number and or as the basis number for an encryption key. The monitoring circuitry having: manipulation circuitry to transform monitored data and combine it with previously manipulated values; and registers to store previously manipulated values; and counters to count events; and condition detection circuitry for detecting when a signal is at a specific value or range of values. Optionally the monitoring circuitry which has the functionality for capturing system properties may be combined with other monitoring circuitry, which has the functionality required by a debug support circuit. The monitoring circuitry avoids replication of resources by sharing parts of specific monitoring circuits like counters.