Quantum key distribution is a technique that permits the secure distribution of a bit string, used as key in cryptographic protocols. The security is guaranteed by suitable coding of the information in a quantum property and from the fact that a quantum cannot be both split and cloned. In this paper, we give details and show the results of an experimental realization of the B92 quantum key distribution protocol in 1550 nm telecom window.Index Terms-quantum key distribution, single-photon detector, light polarization.

In this work, we present active and passive linear optical setups for error correction in quantum communication systems that employ polarization of single-photon and mesoscopic coherent states. The proposed systems are analytically analysed and their applications in quantum communication systems are described. In particular, we show a security analysis of a QKD system employing the active error correction system when an eavesdropper uses the Fuchs-Peres-Brandt attack.

In this work, we propose a quantum bit string commitment protocol using polarization of mesoscopic coherent states. The protocol is described and its security against brute force and quantum cloning machine attack is analyzed.Bit commitment is one of the most important cryptographic protocols that can be used to realize, among others, coin tossing, zero-knowledge proofs and electronic voting.Due to its importance, it was one of the firsts cryptographic protocols that researchers tried to find a quantum version [1][2][3][4], believing that a quantum bit commitment (QBC) protocol could be unconditionally secure. However, it was proved that it is impossible to construct an unconditionally secure QBC protocol using qubits encoded in single-photon pulses [5,6], that is, when Alice sends a single-photon to Bob. Nevertheless, this does not mean that QBC has security similar to classical versions. In fact, limiting the power of the participants, it is possible to construct QBC protocols resistant to some types of attacks [7,8].On the other hand, aiming to improve the performance of practical quantum communication systems (limited by the use of single-photons that are hard to produce,

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