Erik Woodhead, Stefano Pironio
The ideal BB84 quantum key distribution protocol is based on the preparation and measurement of qubits in two alternative bases differing by an angle of pi/2. Any real implementation of the protocol, though, will inevitably introduce errors in the preparation of the states and in the alignment of the measurement bases with respect to this ideal situation. We illustrate the effects of such errors on the security of the BB84 protocol in the case of individual attacks, where necessary and sufficient conditions for security are known. Though the effects of these errors are small for expected deviations from the perfect situation, our results nevertheless show that Alice and Bob can incorrectly conclude that they have established a secure key if the inevitable experimental errors in the state preparation and in the alignment of the measurements are not taken into account. This gives further weight to the idea that the formulation and security analysis of any quantum cryptography protocol should be based on realistic assumptions about the properties of the apparatus used.
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http://arxiv.org/abs/1209.6479
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