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Quantum Cryptography's Reach Extended

Foundation laid for device that will make unbreakable codes usable at any distance

4 min read

1 August 2003—Code makers dream of communicating using quantum states, such as the polarization of photons. Those quantum characteristics can encode and distribute the keys to unbreakable cryptography without fear of their falling prey to an eavesdropper [see ”Making Unbreakable Code,” IEEE Spectrum, May 2002, pp. 40�45]. While that dream has spawned several experimental demonstrations and even near-commercial products, quantum cryptography, as it stands, is severely limited in the distances it can bridge. In recent weeks, however, a number of breakthroughs have extended the distance we can send quantum messages beyond the few tens of kilometers of years past. Even more important to quantum cryptography’s future, physicists are laying the groundwork for so-called quantum repeaters, devices that will allow those messages to be transmitted around the world.

Earlier this year, Andrew Shields and his colleagues at Toshiba Research Europe Ltd. (Cambridge, UK) carried out quantum cryptography by encoding information in the polarization of individual photons sent over 100 km of optical fiber, breaking an earlier record by about 40 km. Photons are less and less likely to be detectable the farther they have to travel. So Toshiba designed new, highly sensitive detectors that can pick out individual photons from background noise. Shields says his detectors makes quantum cryptography possible over metropolitan distances.

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Why the Internet Needs the InterPlanetary File System

Peer-to-peer file sharing would make the Internet far more efficient

12 min read
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Carl De Torres
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When the COVID-19 pandemic erupted in early 2020, the world made an unprecedented shift to remote work. As a precaution, some Internet providers scaled back service levels temporarily, although that probably wasn’t necessary for countries in Asia, Europe, and North America, which were generally able to cope with the surge in demand caused by people teleworking (and binge-watching Netflix). That’s because most of their networks were overprovisioned, with more capacity than they usually need. But in countries without the same level of investment in network infrastructure, the picture was less rosy: Internet service providers (ISPs) in South Africa and Venezuela, for instance, reported significant strain.

But is overprovisioning the only way to ensure resilience? We don’t think so. To understand the alternative approach we’re championing, though, you first need to recall how the Internet works.

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