Matthew Green is on BlueSky Profile picture
May 12, 2024 13 tweets 4 min read Read on X
Telegram has launched a pretty intense campaign to malign Signal as insecure, with assistance from Elon Musk. The goal seems to be to get activists to switch away from encrypted Signal to mostly-unencrypted Telegram. I want to talk about this a bit. 1/
First things first, Signal Protocol, the cryptography behind Signal (also used in WhatsApp and several other messengers) is open source and has been intensively reviewed by cryptographers. When it comes to cryptography, this is pretty much the gold standard. 2/
Telegram by contrast does not end-to-end encrypt conversations by default. Unless you manually start an encrypted “Secret Chat”, all of your data is visible on the Telegram server. Given who uses Telegram, this server is probably a magnet for intelligence services. 3/
Signal’s client code is also open source. You can download it right now and examine the code and crypto libraries. Even if you don’t want to do that, many experts have. This doesn’t mean there’s never going to be a bug: but it means lots of eyes.
github.com/signalapp/Sign…
Pavel Durov, the CEO of Telegram, has recently been making a big conspiracy push to promote Telegram as more secure than Signal. This is like promoting ketchup as better for your car than synthetic motor oil. Telegram isn’t a secure messenger, full stop. That’s a choice Durov made.Image
When Telegram launched, they had terrible and insecure cryptography. Worse: it was only available if you manually turned it on for each chat. I assumed (naively) this was a growing pain and eventually they’d follow everyone else and add default end-to-end encryption. They didn’t.
I want to switch away from that and briefly address a specific point Durov makes in his post. He claims that Signal doesn’t have reproducible builds and Telegram does. As I said, this is extremely silly because Telegram is unencrypted anyway, but it’s worth addressing. Image
One concern with open source code is that even if you review the open code, you don’t know that this code was used to build the app you download from the App Store. “Reproducible builds” let you build the code on your own computer and compare it to the downloaded code.
Signal has these for Android, and it’s a relatively simple process. Because Android is friendly to this. For various Apple-specific reasons this is shockingly hard to do on iOS. Mostly because apps are encrypted. (Apple should fix this.)
I want to give Telegram credit because they’ve tried to “hack” a solution for repro builds on iOS. But reading it shows how bad it is: you need a jailbroken (old) iPhone. And at the end you still can’t verify the whole app. Some files stay encrypted. core.telegram.org/reproducible-b…

Image
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It’s not weird for a CEO to say “my product is better than your product.” But when the claim is about security and critically, *you’ve made a deliberate decision not to add security for most users* then it exists the domain of competition, and starts to feel like malice.
I don’t really care which messenger you use. I just want you to understand the stakes. If you use Telegram, we experts cannot even begin to guarantee that your communications are confidential. In fact at this point I assume they are not, even in Secret Chats mode.
You should do what you want with this information. Think about confidentiality matters. Think about where Telegram operates its servers and what government jurisdictions they work in. Decide if you care about this. Just don’t shoot your foot off because you’re uninformed.

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More from @matthew_d_green

Mar 27
Ok, look people: Signal as a *protocol* is excellent. As a service it’s excellent. But as an application running on your phone, it’s… an application running on your consumer-grade phone. The targeted attacks people use on those devices are well known. Image
There is malware that targets and compromises phones. There has been malware that targets the Signal application. It’s an app that processes many different media types, and that means there’s almost certainly a vulnerability to be exploited at any given moment in time.
If you don’t know what this means, it means that you shouldn’t expect Signal to defend against nation-state malware. (But you also shouldn’t really expect any of the other stuff here, like Chrome, to defend you in that circumstance either.)
Read 5 tweets
Mar 25
You should use Signal. Seriously. There are other encrypted messaging apps out there, but I don’t have as much faith in their longevity. In particular I have major concerns about the sustainability of for-profit apps in our new “AI” world.
I have too many reasons to worry about this but that’s not really the point. The thing I’m worried about is that, as the only encrypted messenger people seem to *really* trust, Signal is going to end up being a target for too many people.
Signal was designed to be a consumer-grade messaging app. It’s really, really good for that purpose. And obviously “excellent consumer grade” has a lot of intersection with military-grade cryptography just because that’s how the world works. But it is being asked to do a lot!
Read 9 tweets
Feb 21
New public statement from Apple (sent to me privately):

“As of Friday, February 21, Apple can no longer offer Advanced Data Protection as a feature to new users in the UK.”
Additionally:

"Apple can no longer offer Advanced Data Protection (ADP) in the United Kingdom to new users and current UK users will eventually need to disable this security feature. ADP protects iCloud data with end-to-end encryption, which means the data can only be decrypted by the user who owns it, and only on their trusted devices. We are gravely disappointed that the protections provided by ADP will not be available to our customers in the UK given the continuing rise of data breaches and other threats to customer privacy. Enhancing the security of cloud storage with end-to-end encryption is more urgent than ever before. Apple remains committed to offering our users the highest level of security for their personal data and are hopeful that we will be able to do so in the future in the United Kingdom. As we have said many times before, we have never built a backdoor or master key to any of our products or services and we never will.”
This will not affect:

iMessage encryption
iCloud Keychain
FaceTime
Health data

These will remain end-to-end encrypted. Other services like iCloud Backup and Photos will not be end-to-end encrypted.
Read 5 tweets
Dec 29, 2024
What is this new setting that sends photo data to Apple servers and why is it default “on” at the bottom of my settings screen? Image
I understand that it uses differential privacy and some fancy cryptography, but I would have loved to know what this is before it was deployed and turned on by default without my consent.
This seems to involve two separate components. One that builds an index using differential privacy (set at some budget) and the other that does a homomorphic search?

Does this work well enough that I want it on? I don’t know. I wasn’t given the time to think about it.
Read 5 tweets
Sep 19, 2024
Most of cryptography research is developing a really nice mental model for what’s possible and impossible in the field, so you can avoid wasting time on dead ends. But every now and then someone kicks down a door and blows up that intuition, which is the best kind of result.
One of the most surprising privacy results of the last 5 years is the LMW “doubly efficient PIR” paper. The basic idea is that I can load an item from a public database without the operator seeing which item I’m loading & without it having to touch every item in the DB each time.
Short background: Private Information Retrieval isn’t a new idea. It lets me load items from a (remote) public database without the operator learning what item I’m asking for. But traditionally there’s a *huge* performance hit for doing this.
Read 14 tweets
Sep 12, 2024
The new and revived Chat Control regulation is back. It still appears to demand client side scanning in encrypted messengers. But removes “detection of new CSAM” and simply demands detection of known CSAM. However: it retains the option to change this requirement back.
For those who haven’t been paying attention, the EU Council and Commission have been relentlessly pushing a regulation that would break encryption. It died last year, but it’s back again — this time with Hungary in the driver’s seat. And the timelines are short. Image
The goal is to require all apps to scan messages for child sexual abuse content (at first: other types of content have been proposed, and will probably be added later.) This is not possible for encrypted messengers without new technology that may break encryption.
Read 4 tweets

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