It now is a lot more clear what's going on here. The discoverer of this issue is basing his argument on the fact that when you verify a fingerprint, you are now confident that your end-to-end encryption won't transparently send your encrypted data to someone with a different keypair. The other side of the argument is that if WhatsApp actually did what you expect, data would be lost when a person switched phones in the middle of someone sending them a message. As a person who doesn't switch phones very often, I would prefer an end-to-end encryption to never send data to a different public key than the one I've used before. I would rather lose data than divulge it to a third party who has the ability to spoof the recipient's phone. This would only come up whenever someone switched their phone when I was sending them a message, so it's pretty rare.<p>To me the trade off is a no brainer, and apparently to Facebook and Whisper Systems the trade off is a no brainer in the opposite direction.
For those not wanting to watch 14 minutes of video, here is the author's blog post explaining the vulnerability: <a href="https://tobi.rocks/2016/04/whats-app-retransmission-vulnerability/" rel="nofollow">https://tobi.rocks/2016/04/whats-app-retransmission-vulnerab...</a>
I could be wrong, but he just puts the sender phone in Airplane mode and then sends a few messages. Then he swaps the sim card from the receivers "Laura's" phone to the government's phone. Then the government's phone is able to view the messages sent while the sender's phone was in Airplane mode. Is that really the vulnerability?
Hmm doesn't WhatsApp puts a red system message when the phone or key is changed?<p>When I talked to my gf the other day noticed it when she switched her work phone.
There was another article claiming there's no backdoor. <a href="https://news.ycombinator.com/item?id=13394900" rel="nofollow">https://news.ycombinator.com/item?id=13394900</a>.<p>Anybody with any ideas what is happening exactly?
The premise here, being that powerful (or technically adept) people may have the capacity to impersonate a phone number, or clone a SIM card.<p>...since that part isn't directly stated, and might not be obvious to everyone.
I think the past few days of back-and-forth about this issue have made a few things clear:<p>1) The double-check was not widely understood as an indicator of any particular security state prior to the attention this has gotten.<p>2) Is it fairly easy to imagine a scenario in which the behavior of WhatsApp can be readily exploited - think of a journalist on the ground in Tahrir Square using WhatsApp to report on conditions, neither expecting nor receiving replies or confirmations, perhaps for hours at a time.<p>3) The matter of whether this is a "backdoor" or not is contentious, but also not terribly important to the stakeholders.<p>4) Moxie wholesale approves of the WhatsApp implementation.<p>5) WhatsApp does in fact provide substantial security for a common and important use case.<p>So, where do we go from here?<p>I think that those of us that care about freedom in the information age well-advised to remember that Moxie has done incredible, substantial, and landscape-shifting work in this space.<p>Nevertheless, I also think that Moxie can provide a few more details and thoughts that will be hugely helpful to the community in thinking through the coming years of IM security.<p>Specifically, I will quote the comment I made in the other article, addressing Moxie directly:<p>Moxie,<p>I think it's fair to say that you are the world thought leader on these matters right now.<p>One thing that the rest of us are wondering right now is:<p>> (Quoting Moxie, in response to my comment) I've been impressed with the level of care that WhatsApp has given to that requirement.<p>To what degree do you really know that? Is there a place where we can read about your interactions with Facebook, the level of access they've given you, and the degree to which they have allowed your recommendations to shape the contours of their implementation?<p>Nothing less than the strength of dissent lies in the balance of questions like these.<p>> I think we should all remain open to ideas about how we can improve this UX within the limits a mass market product has to operate within, but that's very different from labeling this a "backdoor."<p>I agree that the jump to scary terminology is dangerous.<p>However, at the end of the day, I think that many of us have been trying to make a simple point that shows that there is a sort of crossing of that line:<p>WhatsApp claimed that they were simply unable to intercept communications, and now we find out that, without any user interaction or approval, messages which haven't received the "double check" are re-transmitted when a new key is generated.<p>So look: nobody here is trying to diminish your tireless work and your accomplishments in bringing freedom into the information age.<p>But there are nuances here that are important, and fleshing them out is a big part of what this community is about.