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TextSecure's Private Group Messaging

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Re: TextSecure's Private Group Messaging

#31

Post by kobeissl »

tptacek wrote: post #21
kaeporan wrote: post #17

Earlier quoted context omitted.

Thanks for agreeing to turn the discussion in a more constructive direction, Thomas. I agree that mpOTR is a dead end. The initial paper by Goldberg et al describes a protocol that is bulky and largely undefined. I should mention that for those reasons, Cryptocat's group chat effort has been relabelled to "mpCat" instead of "mpOTR" — we're moving on to creating a protocol suitable for synchronous use-cases specifical…

Despite the fact that you've fleshed your responses out from single sentences to whole paragraphs, there is still no technical content in this comment that addresses my comment. It appears that your response is "no, we don't properly do transcript consistency either, but we're working on it". But I had to read between the lines of your name-dropping comment to come to that conclusion. An uninformed reader of your roo…

jesus christ fuck already

Re: TextSecure's Private Group Messaging

#32

Post by kaeporan »

tptacek wrote: post #29
kaeporan wrote: post #27

Earlier quoted context omitted.

UI is absolutely a very difficult part of the problem, and here we see an example outlining this. Even a capable protocol still has problems if the UI fails to translate the capabilities into benefits and security increases for users. I speak from experience: Cryptocat has had some serious issues that were due simply to incomplete UI, the most recent of which was related to authentication. Also, the reason for us mov…

This is a comment that appears to endorse mpOTR's broken transcript consistency feature. Also: formal security proofs? Really? Some context: http://tobtu.com/decryptocat.php (Yes, we know you addressed these issues; the page I just linked to says that).

It really seems like you wrote this comment not to add anything to the conversation, but simply to discourage me from commenting. I really don't understand. I'm trying to be constructive here and I wish you'd join me. Your comment right now just flails around for abrasive things to put together into a statement that is completely incoherent and off-topic.

Re: TextSecure's Private Group Messaging

#33

Post by tptacek »

kaeporan wrote: post #32
tptacek wrote: post #29

Earlier quoted context omitted.

This is a comment that appears to endorse mpOTR's broken transcript consistency feature. Also: formal security proofs? Really? Some context: http://tobtu.com/decryptocat.php (Yes, we know you addressed these issues; the page I just linked to says that).

It really seems like you wrote this comment not to add anything to the conversation, but simply to discourage me from commenting. I really don't understand. I'm trying to be constructive here and I wish you'd join me. Your comment right now just flails around for abrasive things to put together into a statement that is completely incoherent and off-topic.

Your inability to respond to my actual comments appears almost willful. Let's break this down:

* You complained about TextSecure's "lack" of transcript integrity.

* I pointed out that transcript integrity was a prominent feature of the blog post we're talking about, and a feature that the actual TextSecure protocol does vastly better than mpOTR.

* Someone else objected to allusions to TextSecure's transcript consistency feature as vaporware, given that Cryptocat actually has a UI for this.

* I pointed out that the protocol Cryptocat builds that UI on is so bad that you conceded downthread that you're building a new protocol --- you made that concession in direct response to my point about mpOTR's inferior transcript consistency.

* Your response is to imply that improved transcript consistency is not a significant reason for abandoning your existing protocol.

* I point out the inconsistency.

* You object that I'm not "adding anything to the conversation".

Re: TextSecure's Private Group Messaging

#34

Post by [deleted] »

codelike wrote: post #11

I'm a big fan of TextSecure and recommended it to all my friends, both those in IT and 'normal' people. Usually, I managed to convince them that the open source nature of TextSecure and the crypto experts behind it (e.g. Moxie) make it more secure than Threema/... . However, the more sceptical ones among my friends always asked two questions, which I didn't have a good answer for: 1. What is TextSecure's business mod…

[deleted]

Re: TextSecure's Private Group Messaging

#35

Post by kaeporan »

tptacek wrote: post #33
kaeporan wrote: post #32

Earlier quoted context omitted.

It really seems like you wrote this comment not to add anything to the conversation, but simply to discourage me from commenting. I really don't understand. I'm trying to be constructive here and I wish you'd join me. Your comment right now just flails around for abrasive things to put together into a statement that is completely incoherent and off-topic.

Your inability to respond to my actual comments appears almost willful. Let's break this down: * You complained about TextSecure's "lack" of transcript integrity. * I pointed out that transcript integrity was a prominent feature of the blog post we're talking about, and a feature that the actual TextSecure protocol does vastly better than mpOTR. * Someone else objected to allusions to TextSecure's transcript consiste…

Thanks for laying out your thought process, it's very helpful.

> I pointed out that the protocol Cryptocat builds that UI on is so bad that you conceded downthread that you're building a new protocol --- you made that concession in direct response to my point about mpOTR's inferior transcript consistency.

This is the problem. You're assuming that my mention of mpCat was a concession made in "direct response" to your point about mpOTR, whereas it's actually brought up as a tangent. The reason we're building a new protocol is to be able to subject it to formal security proofs, as mentioned prior. It doesn't have to do with the existing protocol being "bad" or not or its current integration into the UI.

Regarding my other implied statements, I think it would be better to stick to claims I am explicitly making instead of assuming implications on my part. That being said, I apologize and will try to be more clear in my future comments in order to avoid assumptions.

I'm also not sure why you keep bringing up mpOTR. As I mentioned in my other post that you refer to, we're not using it anywhere nor do we plan to. We're building a modified version which is far less bulky, etc.

Re: TextSecure's Private Group Messaging

#36

Post by makomk »

phaer wrote: post #18
codelike wrote: post #11

I'm a big fan of TextSecure and recommended it to all my friends, both those in IT and 'normal' people. Usually, I managed to convince them that the open source nature of TextSecure and the crypto experts behind it (e.g. Moxie) make it more secure than Threema/... . However, the more sceptical ones among my friends always asked two questions, which I didn't have a good answer for: 1. What is TextSecure's business mod…

Afaik TextSecures server infrastructure consists mainly of Google Play Services which comes at no financial costs for them but with the downside of depending on Google to temporary store encrypted text.

Yeah. The more substantial downside is that Google effectively has remote root access to every device which holds decryption keys for that text. That's not exactly ideal.

Re: TextSecure's Private Group Messaging

#37

Post by tptacek »

kaeporan wrote: post #35
tptacek wrote: post #33

Earlier quoted context omitted.

Your inability to respond to my actual comments appears almost willful. Let's break this down: * You complained about TextSecure's "lack" of transcript integrity. * I pointed out that transcript integrity was a prominent feature of the blog post we're talking about, and a feature that the actual TextSecure protocol does vastly better than mpOTR. * Someone else objected to allusions to TextSecure's transcript consiste…

Thanks for laying out your thought process, it's very helpful. > I pointed out that the protocol Cryptocat builds that UI on is so bad that you conceded downthread that you're building a new protocol --- you made that concession in direct response to my point about mpOTR's inferior transcript consistency. This is the problem. You're assuming that my mention of mpCat was a concession made in "direct response" to your…

Maybe some other reader can tell me whether Nadim is saying that he endorses TextSecure's continuous transcript consistency model and is working on folding it into his new protocol, or whether he thinks the mpOTR model of consistency checking only at the conclusion of sessions is so useful that not providing it is worth dinging TextSecure over, or whether there's some third option I'm excluding. Because I can't even figure out what Nadim is trying to say anymore.

Re: TextSecure's Private Group Messaging

#38

Post by xyzzy123 »

makomk wrote: post #36
phaer wrote: post #18

Earlier quoted context omitted.

Afaik TextSecures server infrastructure consists mainly of Google Play Services which comes at no financial costs for them but with the downside of depending on Google to temporary store encrypted text.

Yeah. The more substantial downside is that Google effectively has remote root access to every device which holds decryption keys for that text. That's not exactly ideal.

I would be interested in your thoughts on alternative platforms / firmware /ecosystems which get around this?

Re: TextSecure's Private Group Messaging

#39

Post by kaeporan »

tptacek wrote: post #37
kaeporan wrote: post #35

Earlier quoted context omitted.

Thanks for laying out your thought process, it's very helpful. > I pointed out that the protocol Cryptocat builds that UI on is so bad that you conceded downthread that you're building a new protocol --- you made that concession in direct response to my point about mpOTR's inferior transcript consistency. This is the problem. You're assuming that my mention of mpCat was a concession made in "direct response" to your…

Maybe some other reader can tell me whether Nadim is saying that he endorses TextSecure's continuous transcript consistency model and is working on folding it into his new protocol, or whether he thinks the mpOTR model of consistency checking only at the conclusion of sessions is so useful that not providing it is worth dinging TextSecure over, or whether there's some third option I'm excluding. Because I can't even…

I endorse continuous transcript consistency, but believe that TextSecure currently does not allow its users to benefit from it and that this should be resolved. I think mpOTR is irrelevant to this discussion. I hope that's clear!

Re: TextSecure's Private Group Messaging

#40

Post by sdevlin »

kaeporan wrote: post #2

The fact that transcript consistency is waved aside, despite being an essential property of a messaging protocol especially in a group context, is problematic, from my perspective. Consider a group chat between Alice, Bob, and Carol. With this protocol, Alice can selectively send different messages to Bob and Carol with both of them thinking they got the same message. For example, Alice can tell Bob "The funds were t…

> For example, Alice can tell Bob "The funds were transferred, thanks!" and tell Carol "Bob is stealing money." — and the protocol will ascribe integrity to the messages for both participants and label them as the same message.

Isn't this trivially possible in Cryptocat for anyone who controls the server?

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