Argthtjtr

I'm building a world for a role-playing game campaign using the Stars Without Number system.

Some background information first:

Stars Without Number Original Setting: In the original story provided by the SWN book, humanity has reached a post-scarcity level of technology and has traveled and settled to other star systems using (a) FTL travel, and (b) worm-hole-like portals. However, at some point, a cosmic event happened called The Scream which destroyed the portals and drove many people mad across the universe, effectively cutting out colonies from one another. As a result most planets were set back centuries both from a technological and a social/cultural perspective.

Quantum Entanglement Communication: In the Mass Effect series there is a type of communication based on quantum entanglement. The upside of QEC is that it allows two ends to communicate instantly no matter the distance. The downside is that, the way quantum entanglement works, you can only create a communication channel between points A and B, as opposed to other ways of communicating where you can broadcast your message to several/countless endpoints.

My setting:

In my setting FTL travel is being discovered and humanity starts settling on hundreds of nearby systems. There are no wormhole-like portals, the only way to get to a star is via FTL travel.

As it happens every time a powerful nation establishes colonies, Earth attempted to maintain control. The way Earth did that was via setting up QEC systems between itself and most of the planets and acted as central hub of communication for everyone, similarly to how telephone centers used to operate. Remember, the downside of QEC is that it establishes communication only for points A and B. This means that if Colony B wants to send a message to Colony C they will have to go through Earth (Point A).

However, at some point, Earth was overtaken by unbraked/sentient AIs and this communication hub was destroyed leading the colonies to panic and chaos.

My question:

Earth would want to keep QEC technology a secret. Otherwise, some of the colonies may establish QEC systems between themselves. If you attempt to keep the technology secret from a single colony you can guard it using a substantial force. But that becomes increasingly difficult when the colonies number in the order of hundreds. So, how is it possible that Earth kept the how-to of this technology a secret for a long time on so many different worlds?

p.s. There is a similar question however the answers specifically address the scenario described by the OP and thus they are not suitable for my setting.

The technology for locating the quantum entangled pairs is not integral to the actual communication device. In a heavily guarded bunker on Earth, a supercomputer and some very specialized equipment locate a pair of quantum entangled pairs. (Actually two sets of pairs) It then puts one particle from each pair in a transceiver to be transported at FTL to the colony world. The other particle of each pair goes into a transceiver which stays on Earth. Only the technology to use the particles for communication ever leaves Earth. The tech which finds them and isolates them for this usage, stays at home.

In this way, the colony world scientists can fully understand how the communications works (which is vital since they have to maintain their transceiver). But they cannot locate new pairs on their own; so they cannot create communications channels of their own. Earth remains the center of the universe.

If the Internet and all its component parts (routers, DNS servers, certificate authorities, etc) vanished tomorrow, would you know how to rebuild it?

To most people on most of these worlds, the QEC system is "magic" -- not literally magic, but it's there, it works reliably, and for most people that's enough. If the system was installed by experts from Earth and has no user-serviceable parts inside, then there's been no need for people on the remote worlds to become experts or to be granted access to schematics etc.

This doesn't mean that there aren't curious people, tinkerers, and hackers, of course, so this "make it uninteresting + no need to know" policy needs to be accompanied by consequences for people who try to reverse-engineer or hack it. This can take the form of physical security (high-voltage shock if you don't do the secret 17 steps to open the door in the right order), remote surveillance (Earth is immediately alerted and they can remotely monitor and trigger stuff¹), or local policing (this is super-important to us and we can't risk letting you break it,²or this is super-dangerous and we can't risk you getting fried).

¹ Consider the chilling effects if, at setup, Earth installed transmission points in, say, three places on the planet. The response to tampering is a building-flattening explosion plus messages at the remaining locations: "don't do that again". That might disincentivize hacking.

² Doesn't heavy guarding mean it's interesting? Well, depends on how you spin it. Maybe what you're guarding is access to the super-expensive communication channel to Earth -- it's about the money, not the technology. Or maybe it's because this is the "red phone" and only authorized people are supposed to use it. You can have reasons to guard it that aren't about protecting technological secrets, in the same way that protections on ATMs and credit-card readers protect money, not the underlying technology.

Like Henry Taylor's answer, I'm assuming that the entanglement is done in Sol, with them shipping out one half of a pair of something like SIM cards to anyone who wants internet.

TL;DR the same way no one makes backyard nukes: no exact steps, no infrastructure, no institutional knowledge, it's also a military secret

Consider nuclear weapons. A fair number of people on the internet know how they work in the very broad strokes. And yet, the number of nukes built in crazy people's garages is zero. Why's that?

Because going from "smash chunks of sub-critical radioactive rocks together to get a supercritical mass" to an actual nuclear weapon is hard, and that information isn't available on the internet. Likewise, even if the physics behind QECs is publicly available (like nuclear physics) the information needed to actually make QECs is not.

Also, making nuclear weapons requires a lot of specialized, expensive, easy-to-identify infrastructure. Likewise, QEC production could also require some very large and expensive components that are quite obviously for QEC production. As such, not only are potential QEC manufacturers discourged by this high startup cost, it's also obviously going to be a QEC plant to anyone who's looking. More on that later.

There's also the matter of institutional knowledge. Basically, not everything written down is going to be understood, and not everything that needs to be written down will be. "Use water" said the Roman concrete makers, but it took us until very recently to realize that they used salt water. "No duh! You use salt water!" the ghosts of the Romans shouted at the researchers who published that finding. The same thing applies here: knowledge of some steps in the process may not be written down, or they might get misunderstood by whoever reads them much later.

If you want to make microchips, you need a degree. You also need a thousand other people with degrees. Even if one person who knows about making QECs is out of Sol at the time of the Apocalypse, it won't be enough to preserve that institutional knowledge. You're going to need to train a lot of people in how to make QECs, and that's probably going to require a specialized school. There's probably one in Sol, and it's probably mandetory to sign NDAs and/or work for QECcomm or whoever makes them.

But finally, the military is going to want this under control. Why? Because they need to be in communication and synchronize. They also want it centralized because that way they can monitor QEC traffic for intelligence reasons. If a bunch of rebels had QECs that didn't go through a centralized, monitored hub, then it would be much harder to track them down.

Perhaps the QECs on the remote colonies have a 'tamper seal' of sorts that destroys the entanglement if opened/modified. Communication technicians in the colonies could know how to use the QEC but wouldn't be able to actually take it apart.

It is not secret. Earth didn't understand it either.

The communication tech is based on found alien artifacts, discovered on a dead world. Also on this world were clues to FTL travel. FTL was more tractable to hack and copy but the spooky communication technology proved absolutely inscrutable. It is not even certain that the intended primary function of these devices was communication.
Fortunately a fair amount of working devices were found, enough to distribute around and use. But the Earthers were unable to figure out how they worked or replicate any of them.

The technology is not completely secret, or it can be rediscovered by the colonies - but it has an Achilles heel that the Earth Directorate uses to maintain an iron grip: all the communication paths created using this technology are plainly visible to each other in another dimension, and the Earth Directorate destroys any new channels which appear and are in the process of connecting; the Earth Directorate is able to rapidly detect, and destroy, nascent channels because they are much further advanced in this technological regime than the colonies, which are still taking their first steps here.

Destruction of a nascent communication channel in this alternate QEC dimension may cause real-universe destruction of the machinery responsible for forming or controlling the channel. This would repeatedly set back experimentation on the colonies, albeit not permanently. Eventually a colony may figure out what is going wrong and figure out how to defeat the Earth Directorate's brutal ban.

This concept also allows for an unknown "outer space" area beyond the Earth Directorate's purview where unknown parties, much older and more advanced than humanity, lurk. Perhaps some among the Earth Directorate's scientists have seen glimpses of some of their ancient, unimaginably large and apparently strong communication links, but they kept it to themselves and they were unable to learn more because their bosses never authorized them to expand research beyond maintenance and defense within the colony volume...

The concept of a device which the primary government authority uses to prevent others from gaining an equal device is a central component in my all-time favorite book, Alan Dean Foster's "The Peace War".

However in that book, the device is not for communication, it is a weapon, and it is so powerful it actually elevated a minor faction to global authority status prior to the start of the main portion of the tale.

We alredy have that. There are many countries using the internet today that wouldn't be able to rebuild it nor control it if they had to because they lack the industries and the know-how to build or control. You don't have to keep it secret, you just have to keep them poor.

And in the case of wealthy network nodes secrecy would be useless. Using the internet as an example, the technologies needed to rebuild it are naturally present in all rich countries. It may not be a 100mb connection, but it will work.