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On Ghost Users and Messaging Backdoors

blog.cryptographyengineering.com

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Re: On Ghost Users and Messaging Backdoors

#21

Post by jeklj »

RcouF1uZ4gsC wrote: post #9
jeklj wrote: post #5

Earlier quoted context omitted.

Maybe we should consider that goods can still be worthwhile despite their mitigations.

I agree, but when you do that, you need to actually make an accounting of the costs/benefits. If you look among programmers and security specialists on say HN there is not even a debate or discussion about this, but rather an absolutist position that this is good and that the only reason to think this is bad is if you are a totalitarian government wanting to oppress your people.

Yeah yeah, but ultimately this all comes down to whether you think government interception of private messages is ultimately better than the messages staying private. People here obviously don't feel the same way you do about that.

Myself, I'm not quite so convinced as you seem to be of the harm of "absolutist" positions. Maybe the truth isn't always somewhere in the middle

Re: On Ghost Users and Messaging Backdoors

#22

Post by pariahHN »

zzzcpan wrote: post #16
vonseel wrote: post #7

Earlier quoted context omitted.

Signal groups are managed by the client devices. The details are quite complicated, but some are documented here: https://signal.org/blog/private-groups/ Perhaps another user with stronger familiarity on the subject can expand on this (ELI5 would be great!).

Signal client is centrally managed and can be updated for every user. And it's quite ridiculous claim that Signal can't implement a backdoor in the client because of some arbitrary design choice.

Yes but they would have to alter the clients code - this would be reflected in the source and comparing hashes of the binary (as Signal would have to keep that code change out of the public repo). So yes, the design of the system quite effectively prevents a client side backdoor from going unnoticed.

Edit: also, this is a deliberate design choice not an arbitrary one.

Re: On Ghost Users and Messaging Backdoors

#23

Post by gepoch »

zzzcpan wrote: post #16
vonseel wrote: post #7

Earlier quoted context omitted.

Signal groups are managed by the client devices. The details are quite complicated, but some are documented here: https://signal.org/blog/private-groups/ Perhaps another user with stronger familiarity on the subject can expand on this (ELI5 would be great!).

Signal client is centrally managed and can be updated for every user. And it's quite ridiculous claim that Signal can't implement a backdoor in the client because of some arbitrary design choice.

Yeah security is not really "proveable" in any software system.

However, a few points to consider:

1. The signal server can't "see" the group. Clients are just sending N messages to everyone in the group with some encrypted metadata that says it's a group message.

2. The client app is open source. You can go look for a ghost user or backdoor mechanism yourself.

3. The build is reproduceable. You can build it yourself and sideload your own APK, or compare it to the APK coming from the play store.

I don't think it's impossible to put a backdoor in, but I think it at least makes vigilance a good defense. Smart serious people are paying attention.

Re: On Ghost Users and Messaging Backdoors

#24

Post by manicdee »

Spooky23 wrote: post #14
bigiain wrote: post #11

Earlier quoted context omitted.

So we should just go ahead and put Orwell's Telescreens in everyone's house so the governments can see what we're plot^h^hannng all the time? (Looks around the office and sees the Echo and Google Home, remembers how many friends have those and/or Samsung "Smart TVs" in their home, or who have their phones constantly listening for "OK Google" or "Hey Siri". Right. As you were...)

No. The state should be able to get a warrant to intercept communications for reasonable cause, and the accused should be able to litigate the validity of the search.

How will the accused know about the search when they aren’t told about it?

Re: On Ghost Users and Messaging Backdoors

#25

Post by manicdee »

RcouF1uZ4gsC wrote: post #3

With the spread of misinformation and rage using messaging apps that have literally resulted in people getting killed by mobs (see for example https://www.nytimes.com/interactive/2018/07/18/technology/wh... ) maybe we should re-evaluate our belief that making it impossible for governments to see what is spreading through messaging apps is an unmitigated good?

How would the ability to intercept everyone’s communications have mitigated that incident?

Re: On Ghost Users and Messaging Backdoors

#26

Post by pariahHN »

RcouF1uZ4gsC wrote: post #3

With the spread of misinformation and rage using messaging apps that have literally resulted in people getting killed by mobs (see for example https://www.nytimes.com/interactive/2018/07/18/technology/wh... ) maybe we should re-evaluate our belief that making it impossible for governments to see what is spreading through messaging apps is an unmitigated good?

How people use a tool is not the fault of the tool - there is an underlying issue that drives that behavior. It would be like mandating that hammers have to be soft enough that they can't damage a skull because people use them to bash in peoples heads, which yes would prevent hammers from being used as weapons but would render them ineffective at their original purpose.

Re: On Ghost Users and Messaging Backdoors

#27

Post by maxerickson »

gepoch wrote: post #23
zzzcpan wrote: post #16

Earlier quoted context omitted.

Signal client is centrally managed and can be updated for every user. And it's quite ridiculous claim that Signal can't implement a backdoor in the client because of some arbitrary design choice.

Yeah security is not really "proveable" in any software system. However, a few points to consider: 1. The signal server can't "see" the group. Clients are just sending N messages to everyone in the group with some encrypted metadata that says it's a group message. 2. The client app is open source. You can go look for a ghost user or backdoor mechanism yourself. 3. The build is reproduceable. You can build it yourself…

Binaries are not opaque gibberish, it is possible to analyze them.

And of course for major apps, there are people doing so.

Re: On Ghost Users and Messaging Backdoors

#28

Post by maxerickson »

tjoff wrote: post #17
bigiain wrote: post #12

Earlier quoted context omitted.

In a "properly designed system", the service only ever sees public keys not private keys.

If the point of a law is to circumvent encryption you shouldn't be surprised that it doesn't satisfy anyone who wants the encryption to be safe. Either the backdoor works and the system is bad. Or the backoor doesn't work and the system is illegal. At least if the law doesn't have a loophole. So not sure why the article complains about the design whereas the intent and goal are the real issue. Seems like the design w…

Consider that the article may be written for people on the law enforcement/policy side of the debate.

Re: On Ghost Users and Messaging Backdoors

#29

Post by zzo38computer »

merlincorey wrote: post #2

Apparently some researchers from the GCHQ in the UK are proposing that "secure" messaging systems like iMessage and WhatsApp which manage group chats centrally in a manner that bypasses the end to end encryption should: - Add "ghost" users/devices to existing chats - Suppress notifications of these additions to users This would perpetuate a currently known bug in secure communication protocols, effectively turning it…

What is need is open protocols. Users can write their own implementation if they do not want to use the existing ones. WhatsApp uses XMPP according to Wikipedia, so you could implement your own according to XMPP, I suppose. You might also just use your own programs and protocols. If the messages are encrypted with the recipient's key then nobody else can know what is the message, but only that there is a message. So, you can implement encryption on client the server does not need to know about it.

Re: On Ghost Users and Messaging Backdoors

#30

Post by int_19h »

Spooky23 wrote: post #13
vonseel wrote: post #10

Earlier quoted context omitted.

What makes you think these "mobs" used WhatsApp for its security reasons? I'd expect it's far more likely they use WhatsApp because it's the most popular messenger in that part of the world.

People aren’t dumb. Remember Nextel direct connect? It was known that those communications weren’t tappable initially, and for a time every street level drug salesman had them.

The way WhatsApp was used in e.g. Myanmar included group chats involving dozens of random acquaintances - basically the equivalent of gathering in a town square to gossip. Needless to say, there isn't any security to speak of in such an arrangement. Nor did anyone ever complain that WhatsApp encryption is the obstacle. It's the part where everybody can gossip to everybody, with transparent scaling, that enables flash mobs - and it could just as well be a plain text SMS otherwise.
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