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blog.cryptographyengineering.com
- cross-posted to:
- [email protected]
Blog post by crypto professor Matthew Green, discussing what Telegram does (I wasn’t familiar with it) and criticizing its cryptography. He says Telegram by default is not end-to-end encrypted. It does have an end-to-end “secret chat” feature, but it’s a nuisance to activate and only works for two-person chats (not groups) where both people are online when the chat starts.
It still isn’t clear to me why Telegram’s founder was arrested. Green expresses some concern over that but doesn’t give any details that weren’t in the headlines.
Are there any programs that can do e2e in a group chat? My limited knowledge of e2e and encryption makes me think that’d be extremely difficult and even clunkier
Element (really any Matrix client that supports e2ee) but rooms with hundreds I’d people and having encryption enabled is going to to have lots of messages with key exchange errors.
Signal
Ah yes, the metadata collection app for the NSA.
Isn’t Signal’s whole thing that they reduce metadata as much as they can? What do you recommend? Matrix and XMPP certainly aren’t options if you value metadata protection.
The phone number is the most important piece of metadata, and collecting numbers of people who want to use e2ee and are willing to use an app that’s inconvenient, then building graphs of these people and cross referencing the numbers with all the other data the government has is clearly valuable.
Whether other apps are better or worse in terms of collection of metadata is completely irrelevant when evaluating whether Signal itself is safe. However, as far as alternatives go Simplex https://simplex.chat/ seems to be one of the better options.
Even if no chat app protected metadata properly, that’s still an important fact to acknowledge. Furthermore, it may be more important for people to protect their metadata from a specific government that has agency over them. If you live in US or a US protectorate, then data being leaked to the US government is your primary concern.
I mean, Signal has over 100 million downloads on the Play Store alone. Even on the odd chance those phone numbers do somehow end up in the hands of the NSA or whatever the chances of it actually relaying any real information about you is second to none.
Even then, you can’t assume everyone who uses Signal wants to use e2ee explicitly. Some might just like the app’s style, some might have family members who only use Signal, some might have an ethical problem with corporate apps but aren’t computer-brained enough to know how SimpleX or Jabber or some other obscure alternative works.
Is the phone number requirement bad? Yes, absolutely. Does that instantly rule out all opportunity for it being a good app, privacy wise? Definitely not.
Further; privacy should be simple. Signal is designed to be as close to perfect as it can be without compromising too much privacy. They have decided that a phone number is necessary to prevent spam, and to combat the privacy implications of that they have chosen not to block temporary numbers for those who are more concerned.
Private chat apps are useless if noone knows how to use them. Signal tries to fix that, and I think they’re doing a pretty good job even if it does have it’s pitfalls.
I think you missed the point there. The value for the NSA is in knowing which phone numbers communicate with other phone numbers which is precisely the metadata that Signal leaks. This allows you to build networks of users who are doing private communication. Next, you can cross reference the phone numbers with the data from Google, Meta, etc. and then if you see that one of them is a person of interest, then you immediately know the other people they talk to who are now also of interest.
The fact that people keep trying to downplay this is truly phenomenal to me. Once again, Signal is an app that uses a central server based in the US, that almost certainly shares data with the government. Anybody who minimally cares about their privacy should be concerned about this.
Signal is not an app that’s private. Period. If you don’t understand this then you don’t understand what the term privacy means.
Has this been confirmed? I had this theory before but got told this ain’t true…
If the metadata is being leaked then you have to assume it’s being used in an adversarial way. Privacy can’t be trust based. Either the protocol is secure and it guarantees that your metadata is private, or you’re taking it on faith that people operating Signal servers are good actors and will never leak this data to anybody you wouldn’t want them to.
Also worth noting that thanks to US laws, Signal would not even be allowed to say they’re sharing data with the government even if they wanted to.
Even then, you’re jumping to the conclusion that
a) Signal sends this data to the NSA and b) Signal doesn’t protect phone numbers in somr way
Neither of these do I care about enough to keep entertaining this conversation. Goodbye.
Assuming that data that can be leaked is being leaked is the only sensible thing to do if you care about privacy. Clearly this is too difficult a concept for you to wrap your head around.
Thanks for at least being honest that you don’t actually care about privacy. Bye.
Messages app by Apple. Not extremely difficult, but has its trade offs, and easier when all devices share a CA.
CA?
Certificate Authority
Doesn’t the concept of using a CA (which are generally also central authorities) go against the idea of E2EE that only required to (or more) endpoints or am I missing something? Signal group messages (and the protocol/concept behind it) work without a CA. I think I’m missing something, can you connect the dots for me?
The CA is purely a way to provide validation that the endpoints being connected are who they say they are; the actual signing certificates are still private. Apple uses a central directory; Signal depends on certificates linked to one way hashes of phone numbers.
Group chat is a tricky problem and the modern crypto group (moderncrypto.org) talked about it at great length a few years back. I don’t know whether any software exists that incorporates all those ideas, but that’s mostly because I haven’t really been looking for it.
There is the MLS standard now that was explicitly developed with e2ee group chat applications in mind. From what I have read so far, this new standard seems well regarded by cryptography experts.