Tuesday, February 5, 2019

Quantum repeaters are worthless

"University of Toronto Engineering professor Hoi-Kwong Lo and his collaborators have developed a prototype for a key element for all-photonic quantum repeaters, a critical step in long-distance quantum communication," reports Phys.Org. This proof-of-principle device could serve as the backbone of a future quantum internet. From the report:

In light of [the security issues with today's internet], researchers have proposed other ways of transmitting data that would leverage key features of quantum physics to provide virtually unbreakable encryption. One of the most promising technologies involves a technique known as quantum key distribution (QKD). QKD exploits the fact that the simple act of sensing or measuring the state of a quantum system disturbs that system. Because of this, any third-party eavesdropping would leave behind a clearly detectable trace, and the communication can be aborted before any sensitive information is lost. Until now, this type of quantum security has been demonstrated in small-scale systems.
So if this technology becomes commercially available, you can set up a network that would have to be shut down if anyone tries to spy on it.

Or you can use conventional cryptography that has been in common use for 30 years, and continue to communicate securely regardless of how many people might be trying to spy on you.


  1. It would be also good to note that you could easily disrupt your enemey's communication if it shut down every time someone spied on it. Think about the Enigma machine, the allies could listen in all day, but until they were able crack the code, they could do nothing about the germans issuing their encrypted commands right in front of them. If the Enigma machine had shut down the moment the allies listened in....well, that wouldn't have been very useful to the germans in any way, except to tell them the obvious, that the allies had radios.

  2. If they really wanted a secure system, they could use some version of SIGSALY. SIGSALY even gets around possible weaknesses in AES by physically distributing the noise. Otherwise, you can just have a physical swap of keys. It's incredibly cheaper!