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There is no WhatsApp 'backdoor'

whispersystems.org

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Re: There is no WhatsApp 'backdoor'

#51

Post by contravariant »

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…

No there's nothing stopping WhatsApp from lying to you, although if they are then the double checkmark seems like the least of your worries.

As far as I can tell this 'backdoor' is only relevant for the scenario where WhatsApp is not actively malicious, but gets taken over by a malicious entity, which wants to target someone who's disabled updates.

Re: There is no WhatsApp 'backdoor'

#52

Post by matthewmacleod »

quickben wrote: post #16

I don't user whatsapp, but a general question to these that do: Can the server change keys twice? Change once to server keys, ask for the entire history retransmission. Change again to revert to original receipient keys. Will the receipient be prompted in that case?

Change once to server keys, ask for the entire history retransmission.

No. the WhatsApp client will not retransmit messages that have already been acknowledged by the recipient device.

Of course, you'll have to trust that this is the case; but obviously you'd have to trust the the WhatsApp client app isn't backdoored in the first place, so there is no change in security posture.

Re: There is no WhatsApp 'backdoor'

#54

Post by phreack »

azinman2 wrote: post #27
kingnight wrote: post #15

This main flagrant or off-topic, but something that nags at me when thinking about truly secure messaging apps from the App Store: Even with perfect e2e encryption protocol added, what's preventing WhatsApp developers (FB) from adding in a feature of the app: if local.user is "TargetUser007" { takeDeviceSnap(); sendDeviceSnapshotToFBOverSameEncryption(); } Wouldn't this not be ever verifiable unless you ARE that spec…

I'm sure some security researcher somewhere has run the app through a debugger/disassembler to verify exactly this.

Has it happened before in a similar case?

Re: There is no WhatsApp 'backdoor'

#55

Post by na85 »

sebleon wrote: post #18

At the end of the day, it comes down to trusting WhatsApp. Even without a backdoor in their protocol, they can easily do all kinds of things. For instance, it could instruct specific clients to encrypt and send each message twice: one for the recipient, and one for the WhatsApp server. As long as this was off for 99.9% of users, it's unlikely that security researchers would ever detect this.

Trusting WhatsApp == trusting Facebook

I can't think of a company I trust less than Facebook.

Re: There is no WhatsApp 'backdoor'

#56

Post by hackuser »

UncleMeat wrote: post #24
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…

If your threat model includes using a malicious app to send messages then you lose anyway. Nothing can ever be done to send messages securely using whatsapp if the client is neither trusted nor verified. This is true for basically all software that you use.

Open source software can be verified.

Re: There is no WhatsApp 'backdoor'

#57

Post by psranga »

I take this blog post as confirmation that:

1) ANY one message can be intercepted even if the sender exhibits ideal levels of alertness [Whatsapp server drops message to recipient; sends a rekey request with a fake key; message is intercepted since fake key was generated by server. Sender will see a warning if they turned on that setting (default is to show no warning), but it's too late].

2) Only Whatsapp has this vuln, not Signal app.

3) Depending on sloppiness of sender, more extensive interception is possible. [E.g., server not supplying delivery reports + sender doesn't have warning for key changes + sender sloppy about noticing lack of double check mark => full transcript can be generated]

Re: There is no WhatsApp 'backdoor'

#58

Post by zorked »

LinuxFreedom wrote: post #30

We can learn one important thing here - it is not possible to trust closed source software. Enough said, next issue please.

The problem is that we can't trust open source software either.

Software being closed source doesn't make it impervious to analysis. Software being open source does not mean it has been analyzed.

Re: There is no WhatsApp 'backdoor'

#59

Post by runn1ng »

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.

A little. Without reading the Guardian piece, I wouldn't even guess that delivery notifications have anything in common with security properties.

In other words, the messages are secure only when there is a double checkmark, not just a single checkmark. How am I supposed to know that?!? I am not even sure what do the checkmarks mean.

Frankly, that's not a "backdoor", that's just a poorly thought out GUI (in my opinion), that might eventually lead to backdoors with an evil server.

Re: There is no WhatsApp 'backdoor'

#60

Post by enduser »

hackuser wrote: post #56
UncleMeat wrote: post #24

Earlier quoted context omitted.

If your threat model includes using a malicious app to send messages then you lose anyway. Nothing can ever be done to send messages securely using whatsapp if the client is neither trusted nor verified. This is true for basically all software that you use.

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.
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