Importance

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Abstract

A first communication unit (101) comprises: a processor (203) for obtaining local key material defining a first key generating function from a Trusted Third Party (TTP). An identity processor (205) obtaining an identity for a second communication unit (103 and a key generator (207) determines a first cryptographic key from the first key generating function based on the identity. A generator (209) locally generates a perturbation value which is not uniquely determined by data originating from the TTP. A key modifier (211) determines a shared cryptographic key by applying the perturbation value to the first cryptographic key. The second communication unit (103) also obtains key modifying data and uses it to determine a cryptographic key for the first communication unit (101). It then generates possible values of the perturbation value, and subsequently possible shared cryptographic keys. It then selects one that matches cryptographic data from the first communication unit (101). The perturbation value may provide increased resistance against collusion attacks.

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First Claim