Ben Laurie blathering

A Good Use of the TPM?

Back when the TPM was called Palladium I made myself unpopular in some circles by pointing out that there were good uses for it, too, such as protecting my servers from attackers.

Whether that is practical is still an interesting question – it’s a very big step from a cheap device that does some cunning crypo to a software stack that can reliably attest to what is running (which is probably all that has saved us from the more evil uses of the TPM) – but at a recent get-together for privacy and anonymity researchers George Danezis and I ran, Mark Ryan presented an interesting use case.

He proposes using the TPM to hold sensitive data such that the guy holding it can read it – but if he does, then it becomes apparent to the person who gave him the data. Or, the holder can choose to “give the data back” by demonstrably destroying his own ability to read it.

Why would this be useful? Well, consider MI5’s plan to trawl through the Oyster card records. Assuming that government fails to realise that this kind of thing is heading us towards a police state, wouldn’t it be nice if we could check afterwards that they have behaved themselves and only accessed data that they actually needed to access? This kind of scheme is a step towards having that kind of assurance.

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