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There is no WhatsApp 'backdoor'

whispersystems.org

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Re: There is no WhatsApp 'backdoor'

#321

Post by kazinator »

tptacek wrote: post #140
lisper wrote: post #124

Earlier quoted context omitted.

You can demonstrate the presence of a vulnerability in closed source software but there's no way to demonstrate (or even provide evidence of) the absence of any vulnerabilities.

That's identically true of open-source software. To put it in the theoretical terms you're probably most comfortable with: the programming language used to represent a computer program has nothing fundamentally to do with whether it can be verified. Obviously some languages are easier to verify programs in than others, but the gap between assembly and C in ordinary compiled programs is surprisingly small. Open vs. cl…

[T]he programming language used to represent a computer program has nothing fundamentally to do with whether it can be verified.

I would guess that programs in a Turing-incomplete language will be easier to verify than ones in a Turing complete one.

Re: There is no WhatsApp 'backdoor'

#322

Post by [deleted] »

tptacek wrote: post #167
akvadrako wrote: post #160

Earlier quoted context omitted.

Have you ever heard of the obfuscated C contest? Even with the code in front of your face and looking innocent it's hard to see what it does. When you only have decompiled assembly, obfuscation is much easier.

At the binary level, obfuscation is powerful but obvious . Is iOS WhatsApp meaningfully obfuscated?

[deleted]

Re: There is no WhatsApp 'backdoor'

#323

Post by akvadrako »

tptacek wrote: post #167
akvadrako wrote: post #160

Earlier quoted context omitted.

Have you ever heard of the obfuscated C contest? Even with the code in front of your face and looking innocent it's hard to see what it does. When you only have decompiled assembly, obfuscation is much easier.

At the binary level, obfuscation is powerful but obvious . Is iOS WhatsApp meaningfully obfuscated?

You are claiming that it would be easier to detect the obfuscation from the Obfuscated C Contest with only the binary and no access to the source code?

That is logically wrong - otherwise people would simply compile the source before looking for the bad intentions.

Having the source makes detection of backdoors strictly easier. Nothing you've said provides any evidence to the contrary.

Re: There is no WhatsApp 'backdoor'

#324

Post by danenania »

sfifs wrote: post #279
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…

Look if WhatsApp wants to read your messages without you detecting, there's nothing you can really do to prevent it apart from not using WhatsApp. For instance if you're on some list for message interception, they can give you MITMed keys when you first login. Or they can insert some subtle signal that tells the app on your specific phone to ignore key changes and avoid showing notification in some way you would stru…

Doing those sorts of things would leave a trail of evidence, though, since the attacks have to be included in public app store releases. A typical user might not be able to catch trojans in an obfuscated binary, but there are people who can, and the compromised client would be available to anyone who wanted to dig in.

Re: There is no WhatsApp 'backdoor'

#325

Post by kazinator »

jMyles wrote: post #234
tptacek wrote: post #140

Earlier quoted context omitted.

That's identically true of open-source software. To put it in the theoretical terms you're probably most comfortable with: the programming language used to represent a computer program has nothing fundamentally to do with whether it can be verified. Obviously some languages are easier to verify programs in than others, but the gap between assembly and C in ordinary compiled programs is surprisingly small. Open vs. cl…

tptacek, Over the years interacting with you here on HN, I think this basically sums up the worldview that puts you and I at odds: > Open vs. closed-source software is a concern orthogonal to verifiability. Is there a place where you have written at length, defending this assertion? I am open to it. But it does not resonate with my understanding, nor my (substantial, I think) experience in deployments of open- and cl…

Open vs. closed is obviously orthogonal to verifiability. Those who verify software have access to the source, open or not.

More parties have the opportunity to be verifiers of open software. However, a given OSS program might not attract skilled verifiers.

Re: There is no WhatsApp 'backdoor'

#326

Post by akvadrako »

edejong wrote: post #177
akvadrako wrote: post #157

Earlier quoted context omitted.

That's not true. It prevents replay attacks, as I said. More advanced tokens also do more. My bank uses a hardware token for signing transfers and other actions which can include a human readable message or part of the target account number, making MITM much harder.

I'd say the risk of replay attack is not proportional to the risk of authenticating and authorizing on a fully compromised machine. It's comparing a candle light with a blazing fire. A definition issue with regard to "token": I sincerely do not think a device with display and keyboard used to sign transactions can be called "token". I'd say something like: trusted signing processor. But then again, I'm not a security…

Well the big issue is that it prevents future access to your account. Let's say you have a simple 2FA device (no screen) and are using online banking. First you login via a compromised machine. The attacker MITM'ed you, so can see your account.

1. The bank should require a confirmation with your token to send money. If you don't send anything, the attacker can't either.

2. In the future, after the logout timeout, you know the attacker can't even read your account.

It greatly reduces the attack surface you need to worry about. Any attack they do must be right then.

Re: There is no WhatsApp 'backdoor'

#327

Post by fauigerzigerk »

tyfon wrote: post #319
fauigerzigerk wrote: post #315

Earlier quoted context omitted.

The problem is that most security technologies only provide protection against specific attack vectors and attackers under specific conditions. Without understanding these technologies very deeply, they are all creating a false sense of security to some degree. That doesn't make your statement false, just very difficult to apply. That's not to say it can never be applied. There are clearly cases in which people are d…

Yes, security is very hard. But whatsapp markets itself as a secure system when the client just blindly accepts re-keying from the server without notifying the user by default, It could easily have the notification on by default, and when a user turns it off actually explain that you are no longer secure. The very best would of course be to require the users to physically exchange keys whenever they get a new phone e…

I agree that there is much room for improvement. Instead of simply turning warnings on or off, they could let users enable warnings for some contacts but not others.

But my point is that the current approach is not simply "false security". It is incomplete or optional security against specific threats and not others. Depending on a particular user's expectations it may amount to false security. You're right about that. But it's not clear to me that having this sort of security is worse than nothing for the average user.

Also, you have to consider that this sort of optional and partial security used by a very large number of people allows those with real security needs to hide in the crowd. Taking a clear all or nothing approach, as you suggest, would put a bullseye on the back of those who do need security.

Re: There is no WhatsApp 'backdoor'

#328

Post by pepijndevos »

> We believe that WhatsApp remains a great choice for users concerned with the privacy of their message content.

What about meta-data? Even Signal uses Google's push service to send your messages, and WhatsApp is even known to collect meta-data. (IIRC they changed their EULA recently)

Re: There is no WhatsApp 'backdoor'

#329

Post by _b8r0 »

jMyles wrote: post #246
moxie wrote: post #207

Earlier quoted context omitted.

> This allows WhatsApp to MITM. Whatapps can rekey both Alice and Bob, decrypt both their messages from that point onwards (incl unsent messages) and forward them re-encrypted with their real keys. The only notification might be that rekeying warning, if the users have turned it on. In this scenario even the double-checkmarks are present. This is contrary to WhatsApp's claim that even they cannot snoop. You've just d…

Moxie, I think it's fair to say that you are the world thought leader on these matters right now. One thing that the rest of us are wondering right now is: > I've been impressed with the level of care that WhatsApp has given to that requirement. 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 whi…

I've little to add to this, other than the point that the UK's IP Act allows GCHQ (and other UK government agencies) to abuse this issue individually or en-masse against anyone, anywhere, more or less at will.

That's the world we're in now. I respectfully disagree with Moxie's point about key verification. I think the point you raise about easy-to-imagine-scenarios would've been laughed away years ago, but is not only realistic, but also distinctly possible now.

Whatsapp told the original reporter that they had no plans to fix the issue. The question is that in light of mass spying by the intelligence services, what else will Whatsapp not fix?

Re: There is no WhatsApp 'backdoor'

#330

Post by akvadrako »

taneq wrote: post #242
moxie wrote: post #237

Earlier quoted context omitted.

> That defense, which happens to be the only defense, is turned off by default in WhatsApp. > You seem to argue they do so because it's bad UX to present such notification by default. That's - in my humble opinion - like suggesting browsers should turn off TLS chain errors by default because it's bad UX and just proceed with the connection as if nothing happened... One thing we've learned over the years is that secur…

Why are unsigned key changes a 'normal' thing? It'd be trivial to sign the new public key with the old private key, maintaining a chain of trust.

That is basically how 2FA works with Apple devices. You use an old device to approve new ones. Sure, if you lose your cloud account, laptop and phone all at once you'll need to start from scratch. But under normal circumstances it reduces the amount of blind trust.
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