In a mobile communication device, multiple sets of sensor measurement data are obtained, each from a corresponding hardware sensor resident on the device. Insufficiently random data is filtered from each of the data sets to produce random data sets which are combined to produce entropy data which is stored in an entropy data cache. An entropy pool is monitored to determine a level of entropy data available and, based on the level determined, entropy data is provided from the entropy data cache to the entropy pool. Entropy data from the entropy pool is then applied to perform a cryptographic operation such as the generation of an encryption key for encrypting communications sent or received by the mobile communication device.

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