Hacker News new | ask | show | jobs
by infosechandbook 1621 days ago
> XMPP is as secure as Signal nowadays, it implements the same encryption scheme

Signal enforces E2EE, you can't disable it. If XMPP supports E2EE depends on the XMPP clients and servers, so it isn't enforced and can be disabled. Server admins can even inject XMPP messages that look like coming from the legitimate sender. This is far from "secure as Signal."
3 comments
zaik 1621 days ago
> Server admins can even inject XMPP messages that look like coming from the legitimate sender.

How should that be possible if OMEMO is enabled (which is the default in more modern clients)?

link
infosechandbook 1621 days ago
> How should that be possible if OMEMO is enabled (which is the default in more modern clients)?

See https://infosec-handbook.eu/articles/xmpp-aitm/#t5

TL;DR: XMPP clients can't distinguish between legitimate and injected messages, even if OMEMO is enabled. The XMPP client just displays injected messages as an unencrypted message from the sender.

link
zaik 1621 days ago
In Conversations unauthenticated messages are displayed with a red background, whereas OMEMO authenticated messages are displayed in green. They do not look the same.
link
infosechandbook 1621 days ago
Nobody claimed that they look the same.

As mentioned in the linked article, the behavior upon receiving an injected message is client specific. In any way, the injected message is somehow presented to the (non-technical) user who might then be targeted. We all know the same problem exists in the e-mail world.

link
MattJ100 1621 days ago
Signal operators can also inject messages to people. So this is a strange comparison.

What holds true in both systems is that if someone does this, it's detectable thanks to E2EE. Which is the entire point of E2EE.

link
infosechandbook 1621 days ago
> Signal operators can also inject messages to people.

Did you check this, and can you demonstrate a server-side message injection so that the Signal clients display the injected message correctly, leaving the recipient vulnerable to spoofed messages? Would be nice to see for the security community.

> What holds true in both systems is that if someone does this, it's detectable thanks to E2EE.

What also holds true: One system enforces E2EE; for the other system E2EE is optional, depends on the client, and while spoofing could be detected thanks to E2EE, all clients we checked didn't detect it (Gajim, Conversations, Psi+, Profanity).

link
Andrew_nenakhov 1621 days ago
Signal admins too can ship you an app version that would show injected messages like coming from legitimate sender. [1]

However, while you can be your own xmpp server admin, you can't be Signal admin.

[1]: And for god's sake pls don't even start on reproducible builds, nobody really verifies every app updates.

link
infosechandbook 1620 days ago
You just wrote it is "silly" to compare XMPP with Signal while constantly doing it yourself.

> Signal admins too can ship you an app

Or I could just use my own Signal client since it is open-source and there are several working forks such as https://molly.im/. How do "Signal admins" (whoever this is) manipulate these open-source forks?

Instead of providing any proof or details, you just post one assumption after another to distract from obvious problems with current XMPP servers and clients. As soon as we debunk a myth, the next assumption comes up.

link
jancsika 1621 days ago
> Signal enforces E2EE, you can't disable it.

Exactly!

It seems like there is a combination of tenuous assertions being made about XMPP security here, followed by naive questions from people who apparently don't understand the basic feature set of something like Signal. Any clue why this is happening?

link
topdancing 1620 days ago
XMPP is about choice.

I use OMEMO everywhere. However, I do know of people out there who simply do not see the point of OMEMO as, when they are the server admin, OMEMO adds no value over TLS. OMEMO also doesn't make sense in large public groups, cause you're not going to go and verify 100+ people's encryption keys one by one.

OMEMO and end-to-end encryption are also incompatible with keeping a reliable server-side archive of your messages - which will be accessible to all future XMPP clients that you add to your account - which apparently some people want. You can see this at the table at https://conversations.im/omemo/

Meanwhile, you occasionally find people on the Signal subreddit bemoaning that they lost their entire message history with a loved one because some backup file got corrupted and failed to restore or; they lost some device. Here's an example: https://www.reddit.com/r/signal/comments/rbtdtb/

As I said: XMPP is about choice.

link