By IQT News posted 23 Jun 2021

(Space.com) Arqit, which recently announced collaborations with U.S. defense giant Northrop Grumman and the U.K. telecommunications behemoth BT, aims to launch two quantum key distribution satellites in 2023 from Spaceport Cornwall in the U.K. aboard Virgin Orbit’s LauncherOne.
“The problems with fibre optic is that at above about 300 kilometres (186 miles), it’s possible to get some quantum information transmitted but at less than about one bit per second,” David Williams, Arqit chairman and founder, told Space.com. “In a world that talks about megabits per second or gigabits per second, that’s not a practical product. In order to do QKD on a global scale, the only solution is to use satellites.”
However, in the vacuum of space, the information-carrying photons can easily travel across distances of hundreds of miles. A satellite orbiting at the altitude of 430 miles (700 km), such as the Arqit QKD satellites, can provide “a good quality transmission down to Earth,” Williams said.
But Williams (who is also a founder and former CEO of communication satellite operator Avanti) told Space.com that Arqit is “far ahead of the world in launching a commercial [quantum key distribution] service.”
The two satellites the startup plans on launching in 2023 are only part of Arqit’s solution, Williams explained. Arqit is already providing a regional commercial quantum key distribution service through fiber-optic cables using special software that, according to Williams, solves an old conundrum of quantum key distribution.
“The problem is that with the existing BB84 [quantum key distribution] protocol, if you want to send a key between London and New York, both sides benefit from the quantum security of space to Earth transmission,” Williams said. “But the satellite, as it flies over the Atlantic, is storing the key in an ordinary memory device on board, and that could be hacked.”
The satellite could send the quantum-encrypted key to the recipient immediately without storing it on board. But that would only work for certain distances as the satellite would have to “see” the sender and the recipient at the same time. With a low Earth orbit satellite like that of Arqit, that distance would be only about 430 miles (700 kilometers), Williams added.
Arqit, which has some cryptography heavy-weights on its board including Taher Elgamal who is dubbed “the father of SSL”, a widely used protocol that encrypts internet traffic, invented a completely new quantum key distribution protocol which, according to Williams, overcomes the problems of trustless versus global distribution.

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