End-to-end encryption is useless without client freedom

Today, many companies claim to provide “end-to-end encryption” of user data, whether it be text messages, saved pictures, or important documents. But what does this actually mean for your data? I’ll explain what “non-end-to-end” encryption is, why end-to-end encryption is important, and also when it might be absolutely meaningless.

If you just want to read about end-to-end encryption, click here. Otherwise, I’ll start the story all the way back to how computers talk to each other.

A game of telephone in a noisy room

Computer networks essentially operate like a bunch of people yelling at each other at a public gathering, where everyone is kind of hearing everyone else’s messages, but only really paying attention to ones addressed to them. Let’s say I wanted to grab some Chipotle with my roommate. I’d yell “HEY NATHAN, WANNA GET CHIPOTLE?” over this public network, where Nathan would see his name, identify it as a message that is intended for him, and then reply accordingly. Notably, everyone else listening to the network also hears this, and knows that I’m itching to get some Mexican food.

That’s not even the worst part, because well… how does your computer connect to the internet? Your router hears your computer’s message, and passes it through a series of middlemen, who all perform this broadcasting ritual through some local network, until it gets to wherever your computer wanted to talk to in the first place. But in order for the middlemen to pass on the message, they’d have to hear the message, so now my lunch has become a public gathering known to everyone who’s heard or passed on the message.

Encryption saves the day

That’s where encryption comes in. Encryption lets me change the message to something that the middlemen and everyone else listening on the network can’t understand, but the person that I actually wanted to send the message can turn it back into the original. This way, I can be sure no one except Nathan got the memo of where we were grabbing lunch.¹

So the way encryption’s being used here is known as transport encryption, since I’m sending a message somewhere. Transport encryption is standard practice now through a technology called transport-layer security, or TLS, which is used by almost everything that talks to the internet, your browser, your email client, your phone. If it’s not using TLS, it should be considered insecure.

If you’re thinking ahead, you might be thinking that the other place encryption can be used is encryption at rest. This is for documents and pictures that need to sit somewhere in storage for a while but shouldn’t be visible to everyone. Many businesses require that their employees’ laptops use full-disk encryption, so their data doesn’t get compromised.

When you put these together, your data is actually pretty safe from prying hands. If I put some tax documents on Google Drive, it’ll use transport encryption to make sure no one steals my identity while I’m sending it, and encryption at rest to make sure someone breaking into Google won’t be able to just pull the hard drive out and read the files off it.

Two halves don’t equal a whole

It turns out just putting together these two types of encryption isn’t enough. There’s someone else we haven’t protected ourselves against in this case, which is the party responsible for decrypting the transported data and then re-encrypting it at rest. Google can read all the documents I upload to Drive after decrypting it from transit and before encrypting it to disk. Facebook can read all the messages I send to my friends after decrypting it from transit and before re-encrypting it to send to my friends.

And this is a lot smaller of a problem than it was before! Companies usually have privacy policies to protect user data from being used against what they expect, and many industries have laws like HIPAA and FERPA to make sure the people handling your data don’t leak it.

But we don’t have to just trust them on that, because we already know how to protect data from middlemen who are simply taking a message and sending it somewhere else unchanged, like the ISPs from our networks. We just need more encryption!

End-to-end encryption is just encrypting the data in a way that the only parties allowed to read the data are the people it was intended for. Password manager services like 1Password and Bitwarden use end-to-end encryption so that they’re not decrypting your passwords when you store them online, they’re just storing the encrypted data as-is, and then handing it back to your device which then decrypts it offline. Signal famously provides end-to-end encrypted chat, so that no one, not even the government², will be able to read the messages you send if they’re not the intended recipient.

It’s still not enough

End-to-end encryption seems like it should be the end of the story, but if there’s one thing that can undermine the encryption, it’s the program that’s actually performing the encryption. Cryptographic operations are usually handled by clients, but unless you want to sit there adding points on an elliptic curve in a finite field, that client is your device or your browser, not you.

The big problem here is how do you know your device is actually performing the encryption? How do you know the apps on your phone are only sending the data it needs to send, and not a lot more? Traditionally, independent researchers or bounty hunters may reverse-engineer client software and discover that they didn’t quite operate as advertised, but we can’t just rely solely on people from reddit with too much time on their hands to uphold security.

Imagine if Google Drive was actually a physical vault service and the website was just a person you would hand your valuables to to keep safe. They could say “we’re keeping this in military-grade security,” but unless you watched what they did, how do you know they didn’t cheap out on you and just shove it under the mattress where hackers breaking in could just steal everything?

Same applies to Apple’s recent child protection system. Their white paper goes in painstakingly great detail about how photos are protected by “multi-layer” encryption before it’s able to be decrypted by Apple. But typical users are not allowed to pick apart your iPhone to make sure it’s encrypting everything correctly, or that the perceptual hashing algorithm it uses to filter pictures isn’t just trivially flagging everything for manual review.

WhatsApp data is stored unencrypted to the running application in order to store a database of messages locally. Additionally, this database can be backed up to iCloud, and according to WhatsApp themselves, that data is stored unencrypted, which means that it may benefit from transport security and encryption at rest independently, but ultimately the people moving data around are still able to read it.

I’ve also seen discussion of undermining end-to-end encryption in a ghost proposal, a method that abuses multi-party encryption to add in a “ghost” listener, which can be the company or the government or anyone else that the vendor chooses. In theory, this backdoor could be prevented by an open-sourced client that properly checks each recipient to make sure it’s the expected person before encrypting the message and sending it.

Given that end-to-end encryption solely exists because trusting companies that run services is insufficient, it’s safe to say that trusting companies to make client software that act in the interest of their users is just as useless as trusting companies to make services that act in the interest of their users.

What can i do?

Although inconvenient, trusting different vendors for different pieces of this technological assembly line is the best way to prevent it from becoming abused. Many software use open protocols, communication schemes that are agreed upon and freely available to everyone³. Then, independent parties develop and maintain lots of different software that all speak the same protocol, so if you don’t trust a particular service to have an app that doesn’t encrypt its data properly, you can just choose to use a different one by someone who you trust more.

Email is a famous case of this: if I sign up for an email account with Outlook, I don’t have to use a proprietary Outlook client. I could if I wanted, and I imagine that there may be some features that Microsoft has added specifically to the Outlook website and apps, but since they claim to conform to the open email specifications, I can just choose to use a different one.

On top of that, email is federated, which means that if I didn’t like Outlook’s services, I could switch to a different provider and still be able to chat with people on Outlook, unlike many of today’s siloed services where I can’t just message people on Facebook if I only have an account on Twitter, since they don’t talk to each other using the same protocol.

Matrix is a new chat network that also follows in the same spirit as email, but also has the benefits of multi-party encryption. There are multiple apps and servers, and servers can federate with each other using an open protocol. I would strongly recommend people who are interested in privacy to consider it.

Conclusion

Why care? This might just seem to be some superficial political concern by privacy advocates who warn of dangerous edge cases that only matter to people whose rights are being violated by some dystopian government. Well, to put it bluntly, that dystopia is now, and it’s not just the government we should be afraid of, but tech megacorps who possibly have even more power.

We live in a digital world, so it’s important to know how it works and who’s in control.