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Attack of the Week: Group Messaging in WhatsApp and Signal

blog.cryptographyengineering.com

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Re: Attack of the Week: Group Messaging in WhatsApp and Signal

#21

Post by baby »

arkadiyt wrote: post #7
problems wrote: post #3

So they didn't bother to check if the add to group message was from someone in the group? I mean no offense to the developers, but this seems like a fairly basic oversight and quite concerning that respected and popular products didn't get this level of review until now. No crazy cryptographic mess involving improper ordering of authentication or weird random number generation, this is a simple logic bug. One that I'…

> One that I'm sure many of us would have considered if we were implementing it, things like this do get missed too of course, but enough eyes on the design could have caught this. It wasn't a design flaw, it was an insecure-direct-object-reference implementation flaw. IDORs are extremely common, but since the group id is an unguessable 128 bits, the bug can only be used by someone who was already in the group previo…

> These bugs are not big deals

Entirely agree here, these are UI/UX bugs sure, but attacks? Come on...

Re: Attack of the Week: Group Messaging in WhatsApp and Signal

#22

Post by ktpsns »

"Do we trust the WhatsApp server?" -- could be also formulated as: "Do we trust the WhatsApp client?". It is obviously made by the same people. Both are closed source and the protocol is reverse engineered. What's the point if they made an auditing but do not communicate the results? It's probably not too surprising if reverse engineering points out vulnerabilities. It's a fenced ecosystem which claims to establish a secure communication but does not.

Re: Attack of the Week: Group Messaging in WhatsApp and Signal

#23

Post by forkerenok »

bjoli wrote: post #17
jgunsch wrote: post #5

Does anyone know what the disclosure story is here? Have WhatsApp and Signal had a chance to respond?

I follow the development of signal quite a bit. Moxie comitted fixes about what he called "old sins" concerning group messaging. This was quite some time ago, so they have been aware of that it was lacking somehow, possibly even before this was discovered.

I'm not sure what's worse. If they knew it then risks should have been communicated to their user base.

Re: Attack of the Week: Group Messaging in WhatsApp and Signal

#25

Post by brute »

WildGreenLeave wrote: post #11
arkadiyt wrote: post #7

Earlier quoted context omitted.

> One that I'm sure many of us would have considered if we were implementing it, things like this do get missed too of course, but enough eyes on the design could have caught this. It wasn't a design flaw, it was an insecure-direct-object-reference implementation flaw. IDORs are extremely common, but since the group id is an unguessable 128 bits, the bug can only be used by someone who was already in the group previo…

> The real harm comes from regular people reading articles like the Wired one or the famously wrong Guardian one and switching to much worse alternatives, like SMS or Telegram. I can understand why you give SMS as an example, because it is just plaintext. But why Telegram? As far as I know Telegram is probably better secured over a service like Whatsapp. Edit: the latter is an assumption from me, I do not have any cl…

People are in jail because they felt secure using Telegram. It's the kind of people who should be in jail, but nonetheless it is beyond me how anyone could still use it.

Re: Attack of the Week: Group Messaging in WhatsApp and Signal

#26

Post by bjoli »

forkerenok wrote: post #23
bjoli wrote: post #17

Earlier quoted context omitted.

I follow the development of signal quite a bit. Moxie comitted fixes about what he called "old sins" concerning group messaging. This was quite some time ago, so they have been aware of that it was lacking somehow, possibly even before this was discovered.

I'm not sure what's worse. If they knew it then risks should have been communicated to their user base.

I suspect it was more of a "this is old and crufty and isn't how we would do it today".

Guessing the 128-bit number is non-trivial, and once someone has the ability to access the group id, all is already failed.

Re: Attack of the Week: Group Messaging in WhatsApp and Signal

#27

Post by sasas »

ktpsns wrote: post #22

"Do we trust the WhatsApp server?" -- could be also formulated as: "Do we trust the WhatsApp client?". It is obviously made by the same people. Both are closed source and the protocol is reverse engineered. What's the point if they made an auditing but do not communicate the results? It's probably not too surprising if reverse engineering points out vulnerabilities. It's a fenced ecosystem which claims to establish a…

> It's a fenced ecosystem which claims to establish a secure communication but does not.

Your concern extends for all systems that require centralisation. Possibly one example of a chat client which addresses the concerns you raise is Ricochet [1].

Your Ricochet messaging client instance acts as a Tor hidden service. Your add contacts by their ricochet ID which is derived from an onion address. There is no central server / service involved. Everything is direct p2p between your messaging client and your peers.

The source code has been audited by NCC group [2].

It's limited - text only, no attachments, no voice.

If your threat model includes adversaries such as nation states, then this is perhaps the tool to use for simple text messaging.

[1] https://ricochet.im/

[2] https://ricochet.im/files/ricochet-ncc-audit-2016-01.pdf

Re: Attack of the Week: Group Messaging in WhatsApp and Signal

#28

Post by george3383 »

ktpsns wrote: post #22

"Do we trust the WhatsApp server?" -- could be also formulated as: "Do we trust the WhatsApp client?". It is obviously made by the same people. Both are closed source and the protocol is reverse engineered. What's the point if they made an auditing but do not communicate the results? It's probably not too surprising if reverse engineering points out vulnerabilities. It's a fenced ecosystem which claims to establish a…

Having an open source client and server would help how? How would you know the server is running that software? Or that the binaries distributed via the App Store don't have some special spice?

And as far as I know the whatsapp protocol is simply tokenised XMPP.

Re: Attack of the Week: Group Messaging in WhatsApp and Signal

#29

Post by george3383 »

baby wrote: post #19

I wrote a brain dump about my thoughts on that here: https://www.cryptologie.net/article/437/on-real-world-crypto... tl;dr is "I'd say the problem is in the reaction, not in the published analysis."

The problem once again are the journalists making up stuff for clicks. Remove the journalists from the equation and you will see there's no problem.

Re: Attack of the Week: Group Messaging in WhatsApp and Signal

#30

Post by Karliss »

george3383 wrote: post #28
ktpsns wrote: post #22

"Do we trust the WhatsApp server?" -- could be also formulated as: "Do we trust the WhatsApp client?". It is obviously made by the same people. Both are closed source and the protocol is reverse engineered. What's the point if they made an auditing but do not communicate the results? It's probably not too surprising if reverse engineering points out vulnerabilities. It's a fenced ecosystem which claims to establish a…

Having an open source client and server would help how? How would you know the server is running that software? Or that the binaries distributed via the App Store don't have some special spice? And as far as I know the whatsapp protocol is simply tokenised XMPP.

If you have proper end to end encryption protocol and client which correctly implements the protocol without additional backdoors then it doesn't matter what the server runs. If the client is open source you can verify and build it yourself or download the binary from source that you trust.
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