Quantum cryptography [1], the first application of the promising field of quantum information processing, allows to implement secure communications over optical fiber networks by distributing a symmetric cryptographic key. This distribution takes place in two distinct phases. First, a raw key is produced by exchanging qubits over a quantum channel. Second, the raw key is distilled to produce a secure key. The distillation phase requires that the legitimate users communicate over a classical channel. The laws of quantum physics are exploited to reveal attacks performed by an eavesdropper on the quantum channel and to estimate the information he has extracted.
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