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On Ghost Users and Messaging Backdoors

blog.cryptographyengineering.com

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Re: On Ghost Users and Messaging Backdoors

#31

Post by baroffoos »

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?

The problem is this situation is all or nothing. You can't break the encryption only for criminals, its either secure for everyone or its broken for everyone and not just in a way the government can exploit. Hackers will find a way to exploit it as well. Can you imagine the damage if the worlds IM history was leaked. This is probably the most sensitive data in the world.

Allowing governments access to IM history gives them way more power than they ever had. This is not just restoring lost powers. Never has to government been able to see your entire history of every conversation going back for years. I think most of us would be ok if it were actually possible to create a system where only the government after going through proper court process was able to intercept the messages from that time and forward but currently there is no good proposed solution and very dangerous laws like those in australia are being approved.

Re: On Ghost Users and Messaging Backdoors

#32

Post by burkaman »

pariahHN wrote: post #26
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.

I don't think that's entirely true, sometimes tools have only one purpose. It would not be ethical to manufacture nukes and sell them to people, for example.

Even with a messaging app, imagine that you created a new one, and then found that for some reason 90% of your user base is hitmen communicating with their clients. Maybe that's not your fault, but I think you would be ethically obligated to shut it down, or significantly modify it to stop enabling hitmen.

Obviously these are contrived examples, and often in real life it's impossible to make a tool that can't be used for evil. But I don't think you're devoid of responsibility just because you didn't intend for your creation to be abused. If you accidentally created something dangerous, you have an obligation to take reasonable measures to mitigate the danger.

Re: On Ghost Users and Messaging Backdoors

#33

Post by tptacek »

"Ghost users" are also a class of protocol and UX bug in secure messengers that are worth looking for; you will find secure chat programs where it's possible to add a member to a group with a very strong chance of not alerting other members of the group, whereupon the E2E encryption scheme of the system does all the work of decrypting the messages for you.

Re: On Ghost Users and Messaging Backdoors

#34

Post by hinata »

maxerickson wrote: post #27
gepoch wrote: post #23

Earlier quoted context omitted.

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.

Are these analysis efforts publically viewable?

Re: On Ghost Users and Messaging Backdoors

#35

Post by bigiain »

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…

Moxie and Whispersystems have got some interesting thinking around using Intel's SGX:

"Modern Intel chips support a feature called Software Guard Extensions (SGX). SGX allows applications to provision a “secure enclave” that is isolated from the host operating system and kernel, similar to technologies like ARM’s TrustZone. SGX enclaves also support a feature called remote attestation. Remote attestation provides a cryptographic guarantee of the code that is running in a remote enclave over a network.

Originally designed for DRM applications, most SGX examples imagine an SGX enclave running on a client. This would allow a server to stream media content to a client enclave with the assurance that the client software requesting the media is the “authentic” software that will play the media only once, instead of custom software that reverse engineered the network API call and will publish the media as a torrent instead.

However, we can invert the traditional SGX relationship to run a secure enclave on the server. An SGX enclave on the server-side would enable a service to perform computations on encrypted client data without learning the content of the data or the result of the computation."

https://signal.org/blog/private-contact-discovery/#trust-but...

I don't know if they've got that in production yet - and I don't know just how strong the "cryptographic guarantee" of the secure enclave code is, but the fact that they're trying it fills me with joy...

Re: On Ghost Users and Messaging Backdoors

#36

Post by joecool1029 »

bigiain wrote: post #35
gepoch wrote: post #23

Earlier quoted context omitted.

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…

Moxie and Whispersystems have got some interesting thinking around using Intel's SGX: "Modern Intel chips support a feature called Software Guard Extensions (SGX). SGX allows applications to provision a “secure enclave” that is isolated from the host operating system and kernel, similar to technologies like ARM’s TrustZone. SGX enclaves also support a feature called remote attestation. Remote attestation provides a c…

Yeah... about that: https://www.eteknix.com/intel-sgx-speculative-exploit/

Re: On Ghost Users and Messaging Backdoors

#38

Post by xorcist »

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…

> The build is reproduceable. You can build it yourself and sideload your own APK, or compare it to the APK

Have you tried this? Most people seems content that there is some source available and trust the binary. That may not be an option for everyone.

Re: On Ghost Users and Messaging Backdoors

#39

Post by SmellyGeekBoy »

rosser wrote: post #19
Spooky23 wrote: post #14

Earlier quoted context omitted.

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.

That's a little hard to do in a world where this kind of thing is done by National Security Letter.

I'm pretty sure NSLs are only enforceable in the US.

Re: On Ghost Users and Messaging Backdoors

#40

Post by dingaling »

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?

Meta, but this parent comment is a good example of the mis-use of downvoting on HN.

If you don't agree with the poster then engage in debate, don't just click the little arrow to try to grey it into oblivion.

We're all here to learn. Why not learn how to challenge this fairly widely-held view. Imagine you're talking with a 'normal' at a Christmas party and they say that; do you just stomp away singing LALALA?

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