Comment by dan-robertson | Hacker News Reader

Comment by dan-robertson | Hacker News Reader

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If one assumes that WhatsApp are implementing the protocol as well as signal are (which I do), then I think there are three questions in deciding what is more secure:

1. Do you trust Facebook (or open whisper systems) with your metadata/expect them to delete it?

2. How likely are there to be bugs (in the app, not in the protocol itself) which lead to exploits. On the one hand WhatsApp probably have more people working on the app and likely more security people too. On the other hand they may be pushed to add more features and having lots of code churn may introduce security holes.

3. How much work will be put into exploiting each app. On the one hand more people use WhatsApp but on the other, I guess security conscious people may be more likely to use signal.

A known exploit to WhatsApp happened due to 2 with a bug in how audio calls were initiated. I don’t really have a good guess as to how the apps compare on points 2 and 3 but I guess WhatsApp loses on 1. A more practical point is that it’s likely easier to convince someone to use WhatsApp than signal, especially for group chat.

WhatsApp will rekey and send old messages without notifying the user. This means MITM is possible and not always detectable. This is their intended design (but you can change the preference so that you at least get notified when it happens).

(Widely reported, see Guardian article)

That guardian article was pretty bad. It scared a lot of people from WhatsApp (which is still in general mode secure than most options) to text messaging by claiming that this was somehow some huge security flaw.

From WhatsApp’s point of view this was a reasonable ux trade off. It is a major pain point of signal when it does this (particularly in group chats where it is more likely to happen).

But I agree that from a strict security focused point of view this is a disadvantage to WhatsApp.

Sorry, but his is a major security flaw. WhatApp, their mothership Facebook, or any party who can coerce them into doing so (e.g. the US government), can use this to rekey targets with their own keys, virtually undetectable by most regular users, thereby completely MITMing the message exchanges.

Even moxie, who created this stuff, more or less admitted this[0], by saying the rekeying notification is the only defense, but that one is off by default in whatapp last I checked (which moxie confirmed[1]), which makes whatapp insecure by default at the very least. I wouldn't be surprised if WhatApp servers know if this notification setting is on or off, which would enable them to e.g. target people with insecure default settings only to avoid detection.

I already said this in [0], but let's repeat it: This is essentially the same as if a webbrowser would just accept any TLS certificate without showing a warning no matter if valid or the issuer trust.

Sure, this is hard problem to solve UX-wise and user-education-wise, but that doesn't excuse that you advertise your known-and-deliberately-insecure-by-default default-MITMable product as "secure communication using end-to-end encryption".

[0] https://news.ycombinator.com/item?id=13395869

[1] https://news.ycombinator.com/item?id=13396393

Anyone expecting secure messaging from WhatsApp must have Rekeying Notification set ON. Compare it to having a lock installed and using the key to close the lock.

Personally I can not imagine Human Rights Activist having the Rekeying Notification set OFF.

This is not like a lock and using the key. Not in the very least. It has as much to do with a psychical lock as it has to to with a toaster or a banana. Nothing.

>Personally I can not imagine Human Rights Activist having the Rekeying Notification set OFF.

I can. A lot of those people are not tech savvy. And the targets of e.g. the most recent NSO story weren't just activists, but a lot of other people too, politicians, state officials, lawyers, journalists, etc.

And on top of that, this system becomes MITMable as soon as one of the communicating parties has notifications off (or ignores them, which then comes back to the UX and education issue).

'On the one hand WhatsApp probably have more people working on the app'

From a career in software development, I tend to feel that the more devs, the buggier. Maybe, MAYBE (number of QA)/(number of devs) = reliability coefficient.

The size of the red team could also be significantly larger. The more people you have looking for security holes the more likely to find them

Correlates with my experience, too, however size of the QA team is not a reliable indicator. I've seen it first hand where the QA is huge, but doesn't have good devs, only people that point out process flaws.

A QA team is trying to find bugs with the current release. They are not looking for mitm attacks or misuse. That would be more security who are generally looking for more obvious issues at the network level.

Keep in mind also that WhatsApp also demands full access to ALL your contacts in order to really work properly, as opposed to Signal where you just add the people you want to use Signal with

Even of they implement the Signal protocol, they have additional modifications to support ads, which increases the attack surface.

Well, and as pointed out elsewhere the signal protocol only covers messages in transit. How keys are managed, etc. also strongly affect security. In the signal app, the phones own the keys rather than another entity (hence why messages get rekeyed on whatsapp and why you're easily able to load messages on a new phone).

Reread my comment. If you have additional code to support things like ads, you add attack surface for people to find a way to inject code execution in the context of the WhatsApp process, which has access to the decrypted messages.

Does WhatsApp have ads?

They are already onboarding advertisers and will have ads appear in the app very soon. https://www.independent.co.uk/life-style/gadgets-and-tech/ne...

It doesn't. At first, it used an SMS IIRC that charged you a dollar every month or year, not sure. Then they scrapped that and they are now basing the income on WhatsApp for Business, although I don't know if they are charging yet. But as operating costs were actually low, they mostly ran off of papa Facebook's dollars.

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