It really depends on who is behind it and how much political power they have relative to their next election prospects.
And it doesn't come from companies. Originally it comes from academics, but nobody actually gets their copy of AES from Joan Daemen and Vincent Rijmen. It's software on the internet. You can get it from Mozilla or Google. If you can't get it from them then you can get it from anyone at CCC or Debian servers in France or Brazil or your cousin in Russia or the Venezuelan government that loves any excuse to stick it to the US.
But let's pretend they're willing to cut all the fiber and close all the borders to keep encryption from crossing in from other countries. Your proposal is that they're going to go house to house and search your attic for the last of those t-shirts the EFF printed the last time this happened?
Now mind you, that doesn't mean banning encryption would have no effect. It would mean that your bank and your doctor couldn't use it to protect your finances and medical records, and they're the type of organization that could be compelled to comply with such a thing.
As every comms is under surveillance its vastly easier than that. You just need to look for traffic you can't read. And then go after the sender. If you make encrypted communication a criminal offense, that's an easy task.
And what precisely is that supposed to mean?
If I send you a spreadsheet purporting to be "the latest numbers for the current period" but the low bits of each field (which would reasonably be statistically random) are really encrypted data, how do you propose an observer can figure that out?
The amount of ways around this is kind of silly.
And smartphones are pretty close to that. If vendors enforced their walled gardens a bit more and disallowed cryptography apps you would already have a crypto-free zone on billions of devices.
And while we're at it we can prevent traffic accidents by banning the wheel and prevent heart disease by banning food.
Mandating that they (or carriers) should not turn a blind eye because terrorists/think of the children is not a big leap either, because ostensibly rooting is a security flaw anyway.
That way only apps compliant with government regulation (read: backdoored) would run on most devices.
Sure, a small percentage of people might still find their way around it. But should we only care about the most tech-savy while leaving everyone else exposed to a snooping government?
The step from walled gardens to demanding that the the gatekeeper keeps out certain crypto apps is what causes the walls to fall.
If you can't get secure messaging on an iPhone but you can get it on Android or Ubuntu phone and many people start buying competing hardware because of it, Apple would sooner give up the walled garden than lose that much business.
And you can't draw any kind of meaningful distinction between a phone and a 7" touchscreen laptop, so the only way this would actually work is to ban PCs.
Javascript is Turing-complete. Microsoft Office is Turing-complete. So you would have to stop people from running Javascript or Office or shell scripts or Minecraft or graphing calculators.
And you would obviously have to ban anything that resembles a REPL, which might create some difficulties for software development or anyone trying to learn it.
It's not possible for the enemies of general purpose computing to win the war. What is possible is that they be allowed to make the attempt and end up killing lots of innocent people, both figuratively and literally.
If you try to run your "free" software stack inside a javascript engine inside an approved browser inside an approve operating system then your data is neither secure nor do you actually have control over the execution.
If they can blacklist apps they can also blacklist domains from which you load javascript. It cascades down and you're basically retreating to the position where you say "as long as I can do some computation everything is fine".
It's not fine if you lose control over more and more parts of your computer.
You think laptops are safe? Think about secure boot and those Windows RT devices which do not boot linux despite being capable ARM devices.
But people currently buy iPhones because they want iOS. When there is a jailbreak vulnerability in iOS, they install the patch that closes it because they want to keep using iOS. And if they want to run Android or Ubuntu, they don't buy an iPhone, and they don't have to.
If tomorrow the only hardware you can get runs iOS or Windows RT then people who want something else will keep using today's hardware, in exactly the same way and for the same reasons as normal people keep using Windows 7 and nobody buys Windows RT. And they'll keep doing that until there is a jailbreak vulnerability in the new hardware. Then they won't install the patch, they'll use the vulnerability to wipe the unwanted OS and replace it with something else (or have someone else do it, but the more common it becomes the easier it gets).
The other obvious problem is that today Apple doesn't want you to jailbreak iOS. They try really hard to prevent it and still people can do it, and those people don't even have a huge incentive because you can still buy hardware that doesn't need a jailbreak. You try to impose that requirement by law on all the vendors who don't care and are selling to customers who are being forced into it and see how well it stops even everyday people from removing the backdoor or installing free software.
It would be a disaster of epic proportions. Every law abiding company would have to instantly shut down. All the stock markets would go to zero. The whole country would basically be reset to nothing. Millions would die.
T-shirt in question: https://upload.wikimedia.org/wikipedia/commons/9/96/Munition...
How successful has been the war on movie and music piracy? And the war on leaked documents?
A government can certainly make most if its residents give up on cryptography. But it takes more severe measures than banning a device or another.