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WhatsApp Security Vulnerability

schneier.com

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Re: WhatsApp Security Vulnerability

#31

Post by aidenn0 »

folex wrote: post #2

I didn't quite grasp why attacking entity (e.g. government) has the ability to read messages. What does "WhatsApp has the ability to force the generation of new encryption keys for offline users" mean? Does it mean that WhatsApp backend has the ability to force sender to use pregenerated compromised key provided by attacker? In terms of WhatsApp security whitepaper, does that mean that attacker can force sender to us…

Let's say WhatsApp wants to read the next message sent to user X:

1) WhatsApp makes user X appear offline

2) User Y sends user X a message

3) WhatsApp sends user Y an indication that user X's key has changed, along with the public key for which they have the corresponding private key

With these steps, user Y's message will be resent with the new key that WhatsApp knows, and so they can read the message. There is a configuration setting that will display a notification that the key changed, but no way to prevent an undelivered message from automatically being resent with the new key.

Re: WhatsApp Security Vulnerability

#32

Post by Fnoord »

beambot wrote: post #8
ckastner wrote: post #5

The article mostly just quotes two other sources that have already been discussed here: WhatsApp backdoor allows snooping on encrypted messages , https://news.ycombinator.com/item?id=13389935 There is no WhatsApp 'backdoor' , https://news.ycombinator.com/item?id=13394900

Yep, this is an analysis by a trusted individual in the security field. His ultimate summary: > [WhatsApp's representative is] technically correct. This is not a backdoor. This really isn't even a flaw. It's a design decision that put usability ahead of security in this particular instance.

I prefer this quote by Bruce Schneier. FTA:

> How serious this is depends on your threat model. If you are worried about the US government -- or any other government that can pressure Facebook -- snooping on your messages, then this is a small vulnerability. If not, then it's nothing to worry about.

Re: WhatsApp Security Vulnerability

#33

Post by aylons »

xorcist wrote: post #24
aylons wrote: post #14

While people discuss about a possible state-actor stronghanding WhatsApp and the semantics of backdoor, the "design feature" of not showing the key changes are making real victims, at least in Brasil: The attacker first try to duplicate the mobile phone number of the first victim, probably by social engineering their phone company. This part may look difficult to do, but it is not hard if you realize you do not need…

> WA has no login, no password, so anyone receiving the SMS can impersonate anyone That sounds like a fatal flaw. Could not any GNU Radio user dump these by the thousands?

I don't believe it could be done by the thousands, it would be way more targeted:

You'll need to be next to the actual phone number user when you request, and the victim will receive the SMS. Also, the victim would be shut out of WhatsApp (it allows only one client to be active), which would probably trigger some reaction.

Sounds like a nice hack, nevertheless.

Re: WhatsApp Security Vulnerability

#34

Post by antihero »

FabHK wrote: post #15
pfg wrote: post #10

Earlier quoted context omitted.

That's why WhatsApp allows you to verify your recipient's key out of band. The scenario you describe would cause the identity key to change and trigger a notification if one of the potential clients has that option enabled. There's really no way to avoid out-of-band key verification in end-to-end encrypted messaging unless you fully trust the service. Other than that, the best you can hope for is after-the-fact detec…

> The scenario you describe would cause the identity key to change and trigger a notification if one of the potential clients has that option enabled. ... and that notification would be shown after that potential client's WhatsApp client had re-encrypted the undelivered messages and re-sent them.

So they could effectively leave the phone off for a while, then pop in the SIM and suck up any messages that had been sent in the mean time, and only then would the warning come up?

Re: WhatsApp Security Vulnerability

#35

Post by mschuster91 »

sschueller wrote: post #19
mschuster91 wrote: post #12

Earlier quoted context omitted.

> The scenario you describe would cause the identity key to change and trigger a notification if one of the potential clients has that option enabled. But only for messages sent by the sender AFTER the key-change notification. Those still in the send queue get re-encrypted with the new key of the cop phone and then resent without confirmation, and this is the attack window and the bug! Oh, and most people don't enabl…

How does Whatsapp re-encrypt a message if they aren't supposed to have a key to decrypt? Is this done on the senders phone? Is it possible to re-encrypt within decrypting?

No, the WA server sends the changed public key of the recipient to the client, which has the unencrypted messages. Then the client reencrypts all pending messages and resends them.

Re: WhatsApp Security Vulnerability

#36

Post by mschuster91 »

antihero wrote: post #34
FabHK wrote: post #15

Earlier quoted context omitted.

> The scenario you describe would cause the identity key to change and trigger a notification if one of the potential clients has that option enabled. ... and that notification would be shown after that potential client's WhatsApp client had re-encrypted the undelivered messages and re-sent them.

So they could effectively leave the phone off for a while, then pop in the SIM and suck up any messages that had been sent in the mean time, and only then would the warning come up?

yup

Re: WhatsApp Security Vulnerability

#37

Post by pfg »

agd wrote: post #25

The question for me is that posed by the hacker who discovered the vulnerability. Here's what he said [1]: "He (Moxie) said: “The choice to make these notifications ‘blocking’ would in some ways make things worse. 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 man-in-the-middle transparently and who it coul…

The blocking would occur when the server changes the identity key of a user. If the server does that with the goal of finding out if the user has enabled safety number change notifications, it could just change the identity key to one under the server's control and see whether it receives any garbage.

Re: WhatsApp Security Vulnerability

#38

Post by arrakeen »

conspicuously missing from this discussion is the self-healing capabilities of the signal protocol, which as far as i understand is a major feature. when marlinspike says, "This is called a \"man in the middle\" attack, or MITM, and is endemic to public key cryptography, not just WhatsApp," i find it odd that he wouldn't even address the fact that the signal protocol has protections against this built into the protocol.

Re: WhatsApp Security Vulnerability

#39

Post by kemayo »

agd wrote: post #25

The question for me is that posed by the hacker who discovered the vulnerability. Here's what he said [1]: "He (Moxie) said: “The choice to make these notifications ‘blocking’ would in some ways make things worse. 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 man-in-the-middle transparently and who it coul…

I think you're using a different meaning of "blocking" than Moxie is. I believe they mean "blocking" in the sense of waiting for the user to confirm that the message should be re-sent -- i.e. blocking on the user's input. Whereas you're using "blocking" to mean refusing to re-encrypt the message.

Presumably any message which would be detectable enough as garbage to not be displayed on the reader's phone could be treated as them having this feature enabled, allowing the information-leak Moxie mentioned.

(To be clear, I do think there's a argument to be had over which of these leaks is worse. I just don't think this suggested approach actually addresses Moxie's concern.)

Re: WhatsApp Security Vulnerability

#40

Post by andrewpi »

aylons wrote: post #14

While people discuss about a possible state-actor stronghanding WhatsApp and the semantics of backdoor, the "design feature" of not showing the key changes are making real victims, at least in Brasil: The attacker first try to duplicate the mobile phone number of the first victim, probably by social engineering their phone company. This part may look difficult to do, but it is not hard if you realize you do not need…

Whatsapp does have the option to add a password to your account: http://www.androidpolice.com/2016/11/10/whatsapp-enables-two...
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