Device-independent quantum key distribution aims to provide key distributionschemes whose security is based on the laws of quantum physics but which doesnot require any assumptions about the internal working of the quantum devicesused in the protocol. This strong form of security, unattainable with standardschemes, is possible only when using correlations that violate a Bellinequality. We provide a general security proof valid for a large class ofdevice-independent quantum key distribution protocols in a model in which theraw key elements are generated by causally independent measurement processes.The validity of this independence condition may be justifiable in a variety ofimplementations and is necessarily satisfied in a physical realization wherethe raw key is generated by N separate pairs of devices. Our work shows thatdevice-independent quantum key distribution is possible with key ratescomparable to those of standard schemes.
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