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There is no WhatsApp 'backdoor'

whispersystems.org

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Re: There is no WhatsApp 'backdoor'

#71

Post by jMyles »

tyrust wrote: post #9

>The WhatsApp clients have been carefully designed so that they will not re-encrypt messages that have already been delivered. Once the sending client displays a "double check mark," it can no longer be asked to re-send that message. This prevents anyone who compromises the server from being able to selectively target previously delivered messages for re-encryption. Can this be verified? Can this be verified to be th…

Isn't it possible (in fact trivial) to sniff the traffic generated by WhatsApp and verify that it is indeed the message transmitted, encrypted by the key on the device?

Has anyone performed such an audit?

Re: There is no WhatsApp 'backdoor'

#72

Post by tucif »

MichaelGG wrote: post #46
tucif wrote: post #22

Earlier quoted context omitted.

He does address this: Once the sending client displays a "double check mark," it can no longer be asked to re-send that message. That means a user is able to verify visually that the end-to-end is working. "users might not notice" doesn't seem to me as a strong argument to state this as a backdoor. This would imply not noticing that you don't have a green padlock on chrome is a backdoor too, and it clearly is not.

Couldn't the server change keys after every message? The delay would be fairly small. Hold the original, change key, retransmit, change key back? Guess that is easily enough mitigated if the client won't allow switching back to the same key.

It could.

I guess the point here is: Can there be a backdoor in whatsapp? Of course!

Is there a backdoor on Whatsapp as described on the guardian article? No.

Can the UX be improved to alert the smaller percentage of users that rely heavily on the encryption features when their communication is not being actively protected without disturbing the UX of the rest of the users? Probably yes,

Re: There is no WhatsApp 'backdoor'

#73

Post by halomru »

enduser wrote: post #60
hackuser wrote: post #56

Earlier quoted context omitted.

Open source software can be verified.

Source code can be verified. Binaries distributed via app stores may or may not have behavior different from the published code.

Any open source project can allow you to verify binaries by making builds reproducible. The fact that most apps don't do this is indeed a security problem, but one that's far from unfixable.

Re: There is no WhatsApp 'backdoor'

#74

Post by ploxiln »

tucif wrote: post #22
jMyles wrote: post #5

Color me still-unconvinced. This retort does not address the fundamental point made in the Guardian piece: > “[Some] might say that this vulnerability could only be abused to snoop on ‘single’ targeted messages, not entire conversations. This is not true if you consider that the WhatsApp server can just forward messages without sending the ‘message was received by recipient’ notification (or the double tick), which u…

He does address this: Once the sending client displays a "double check mark," it can no longer be asked to re-send that message. That means a user is able to verify visually that the end-to-end is working. "users might not notice" doesn't seem to me as a strong argument to state this as a backdoor. This would imply not noticing that you don't have a green padlock on chrome is a backdoor too, and it clearly is not.

The "green padlock" was not considered enough because users would not be able to differentiate it from a big lock symbol within the page. Thus we got HSTS.

(There was a time when browsers would color the entire URL bar yellow to indicate https, but that went out of favor many years ago.)

Moxie deserves respect for the web vulnerabilities he discovered and raised awareness about years ago, and for his general competence at cryptography. But in recent years he's shown himself to be willing to make catastrophic sacrifices to make security applications popular and viable for the "lay person".

If the "lay person" ignores the non-obtrusive key changes, and difference between single and multiple checkmarks (and the timing of them, whether single changed to double after a key change), and just trusts that "I heard WhatsApp is secure, so I'm good to go", then so much is sacrificed that there wasn't any point in the exercise to begin with. Except that real solid systems, with direct user control over key continuity, and fully open-source, are undermined by the confusion with these "lay person" super-convenient closed-source systems.

Re: There is no WhatsApp 'backdoor'

#75

Post by jMyles »

FiloSottile wrote: post #61
jMyles wrote: post #5

Color me still-unconvinced. This retort does not address the fundamental point made in the Guardian piece: > “[Some] might say that this vulnerability could only be abused to snoop on ‘single’ targeted messages, not entire conversations. This is not true if you consider that the WhatsApp server can just forward messages without sending the ‘message was received by recipient’ notification (or the double tick), which u…

It wouldn't be a conversation. The attacker would have to rely Alice's messages to Bob before switching the key. But then if the attacker let Alice (the target) receive Bob's messages they will learn theirs got delivered and the attack would fail. So it only works once against a string of messages with no replies. That's not a conversation.

Another thing that's not clear to me: Is the receipt confirmation from Bob (used as the basis for the double-check) signed by Bob?

Re: There is no WhatsApp 'backdoor'

#76

Post by besselheim »

MichaelGG wrote: post #65
kingnight wrote: post #34

Earlier quoted context omitted.

Are reverse engineering techniques currently greater than known ability to obfuscate compiled iOS code?

And it'd have to work for other platforms, too. Android is Java right? Which is even easier to RE.

Android apps can also contain native code. Indeed, WhatsApp includes such libraries, to help with Curve25519 encryption, video encoding, voice over IP, and other functionality.

Re: There is no WhatsApp 'backdoor'

#77

Post by thesimon »

enduser wrote: post #60
hackuser wrote: post #56

Earlier quoted context omitted.

Open source software can be verified.

Source code can be verified. Binaries distributed via app stores may or may not have behavior different from the published code.

> Source code can be verified

But how often is that really done? And to be honest, it can be quite hard to spot critical bugs or backdoors, just look at http://www.underhanded-c.org/

Re: There is no WhatsApp 'backdoor'

#78

Post by tptacek »

avn2109 wrote: post #40
jMyles wrote: post #5

Color me still-unconvinced. This retort does not address the fundamental point made in the Guardian piece: > “[Some] might say that this vulnerability could only be abused to snoop on ‘single’ targeted messages, not entire conversations. This is not true if you consider that the WhatsApp server can just forward messages without sending the ‘message was received by recipient’ notification (or the double tick), which u…

Regardless of the merit of this specific accusational-and-denial cycle, the fact remains that Whatsapp is closed source crypto and there is no way in principle for the user to verify any security claims. I happen to trust Moxie's principles, but not as much as I distrust the relationship-with-government imperatives implied by FB's vast business interests.

There's "no way in principle"? How is this whole story not evidence to the contrary? The person who found this didn't use WhatsApp source code.

Why do you feel that there's no way to verify closed-source software?

Re: There is no WhatsApp 'backdoor'

#79

Post by frandroid »

joeblau wrote: post #23

There seems to be a pretty clear war going on between engineers and journalists lately. - Chris Latter [1] vs Business Insider [2] - Elon Musk vs (Bunch of outlets) - Moxie vs The Guardian I feel like journalists want to write a compelling story and engineers are on the other side like "No, those aren't facts!" I don't follow a lot of media outlets but it seems like journalists either lack the skills or don't care ab…

It would be a war if all these people were allied together. Neither the engineers nor the outlets mentioned here are allied parties. They're disparate across the board.

Re: There is no WhatsApp 'backdoor'

#80

Post by jlgaddis »

cypherpunks01 wrote: post #44
ycmbntrthrwaway wrote: post #12

> That would leak information to the server about who has enabled safety number change notifications and who hasn't , effectively telling the server who it could MITM transparently and who it couldn't; something that WhatsApp considered very carefully. I am not convinced. Why should this option exist at all? Even worse, it is disabled by default. Just enable notifications for everyone and demand verification. If you…

If we're talking about key change notifications, isn't SSH the thing that throws the following error when a key changes? @@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@ @ WARNING: REMOTE HOST IDENTIFICATION HAS CHANGED! @ @@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@@ IT IS POSSIBLE THAT SOMEONE IS DOING SOMETHING NASTY! Someone could be eavesdropping on you right now (man-in-the-middle attac…

FYI: indent those lines a few spaces for proper formatting.
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