Quantum key distribution (QKD) promises information theoretic secure key as long as the device performs as assumed in the theoretical model. One of the assumptions is an absence of information leakage about individual photon detection outcomes of the receiver unit. Here we investigate the information leakage from a QKD receiver due to photon emission caused by detection events in single-photon detectors (backflash). We test commercial silicon avalanche photodiodes and a photomultiplier tube, and find that the former emit backflashes. We study the spectral, timing and polarization characteristics of these backflash photons. We experimentally demonstrate on a free-space QKD receiver that an eavesdropper can distinguish which detector has clicked inside it, and thus acquire secret information. A set of countermeasures both in theory and on the physical devices are discussed.

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The use of Wireless Mesh Networks has growing use in areas without telecommunication infrastructure. One of the main problems is the network performance due to the low capacity of the processors used in intermediary mesh nodes. We propose a hardware implementation of IP Checksum incremental update in FPGA (Field Programmable Gate Array) or ASIC (Application Specific Integrated Circuits). Then, this implementation is compared with the kernel Linux TCP/IP implementation.Resumo-O uso das Redes Mesh está crescendo emáreas sem infraestrutura de telecomunicação. Um de seus principais problemasé a performance de rede devido aos processadores de baixa capacidade usados em nós intermediários. Neste trabalho, e proposta uma implementação em hardware do Recálculo Incremental do IP Checksum em FPGA (Field Programmable Gate Array) ou ASIC (Application Specific Integrated Circuits). Então, esta implementaçãoé comparada com a implementação em software da pilha TCP/IP do kernel Linux.

This works brings an optical setup for one-way quantum key distribution in the frequency domain. The optical setup and the quantum protocol are described and the security analysis is performed.