And yes — I believe my work on Cryptocat does grant me some helpful perspective on the kind of issues faced in group chat. I'm more than happy try my best to offer some insight to other great open source projects. If I wanted to sneakily hide that I work on another encrypted messaging project (why would I? Open source projects discuss issues with one another all the time) it would have been simple for me to create another username.
https://hn.algolia.com/?q=author%3Akaeporan#!/comment/foreve...
I am, however, happy to attack your project, Cryptocat, which I believe to be incompetently interviewed, debugged into existence, and dangerous to its users.
Finally, you still haven't responded to my comment upthread.
The TextSecure protocol retains forward secrecy at the message layer and provides continuous transcript integrity. The TextSecure client hasn't worked out the UI for it, but the protocol supports it. TextSecure can provide continuous transcript integrity with a UI update --- something mpOTR clients can't do at all.
But here you are, sniping at TextSecure for lacking a UI feature that you've implemented a minimal and un-useful version of. Then, when called on it, you retreat to a position of "I'm inspired by TextSecure and am just trying to help". As if, after blogging about why transcript integrity is literally one of the reasons TextSecure doesn't use mpOTR, they were unaware of the importance of the feature.
mpOTR is a dead end. It's unfortunate you invested in it, but that is what it is.
This is apparently so much the case that Nadim has acknowledged jettisoning his existing protocol to come up with a new protocol that will support it.
You could disagree with me, but I don't think you can do so without acknowledging that the comment that introduced this issue to the thread was... let's say "not fully informative".
Also, the reason for us moving to a new protocol has more to do with formal security proofs than being able to adopt new properties.
Some context: http://tobtu.com/decryptocat.php
(Yes, we know you addressed these issues; the page I just linked to says that).
* 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".
> 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.
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 specifically (since TextSecure already has the asynchronous use-case figured out) without shouldering the bulkiness and obsolete nature delineated in mpOTR's original description. One of the things that is actually addressed better is transcript consistency: in mpCat, it will function on a level of reliability that is in fact continuous and not just occurs once per entire conversation.
We recently concluded mpCat's first review summit, and were very lucky to have the feedback of experts such as Trevor Perrin, Joseph Bonneau and Ximin Luo. We also invited members from TextSecure's team in order to help us understand the use-cases scenarios they have experience in. For what it's worth, the TextSecure members that were invited were seen as open source peers, and not as "competitors" as you put it. I should mention that TextSecure's research frequently came up while working on mpCat, and that they are contributing more to this field than most other projects. That's why I say they are inspiring.
An uninformed reader of your root comment on this thread would be surprised by that concession. Is my conclusion incorrect, or was your original comment deceptive? (Unintentionally, I'm sure.)
Just as a note, I'm sincerely discouraged from attempting to have an informative discussion with you by the fact that you keep assuming bad faith on my part, and generally responding in a needlessly rude and aggressive fashion. Consider that your general approach in this particular discussion might be why information security has a bad name as a poisonous field. If I don't reply to parts of your post, consider that it is because they are phrased in a way that assumes and implies a complete understanding, wrapped in aggression and the assumption of bad faith. I'm not here for that kind of discussion.
People can decide for themselves whether you meant to "point out a current problem in the protocol design" (a confusing question, given that your objection is about UI). You know what I think already.
Are you sure this is correct? From the blog post, it seems like this is impossible:
https://whispersystems.org/blog/images/groups-pairwise-optim...
However, there’s an optimization we can make for longer messages and media. The sending client generates an ephemeral symmetric key K, encrypts the message with K (C = EK(P)), and then transmits a single copy of the ciphertext (C) along with the pairwise encryptions of the plaintext hash and the small key K:
So, when a client wants to send a message to the group (like "How are you?") under this scheme, the client encrypts the message using a random encryption key K, yielding message ciphertext C. The client transmits to the server, then the server sends C to every other member of the group.
Since C can only be decrypted by someone who knows K, our client must of course send K to every other member of the group. This is easily accomplished: the client encrypts K once per other member. So, if there are N members in the group, this yields N-1 small ciphertexts. Let's call them "key ciphertexts". These "key ciphertexts" are sent to the server and routed to the appropriate recipient, who decrypts it, thus receiving K. Then the recipient decrypts C using K, yielding the client's original message ("How are you?").
So even though the client is indeed generating a ciphertext per recipient, that ciphertext contains nothing but the decryption key K. It doesn't contain the client's actual message. The actual message is contained in ciphertext C, which is generated by the client and sent to the server only once, and C is relayed verbatim to every other member. That's why I say your attack seems impossible: every member has the same message ciphertext, C, so there's no opportunity for a malicious client to send different message ciphertexts to different clients.)
As long as TextSecure uses this implementation of group messaging, then your attack shouldn't be possible, right?
As far as I know, it isn't possible for an attacker to generate a message ciphertext C such that two different decryption keys would both decrypt to valid plaintexts. There can only be one valid decryption key; trying to decrypt C using any other key would yield random output, wouldn't it?
https://news.ycombinator.com/item?id=7701510
Does your transcript consistency rely on the security of your server?
Zed Shaw was right: http://zedshaw.com/essays/thomas_ptacek_should_apologize.htm...
I agreed so much so that when I was invited to speak at CUSEC shortly thereafter, I was videotaped on stage opening my talk apologizing to him.
Zed didn't update his post on his site to account for that, although he was aware both of my plan to apologize (we spoke on the phone and I agreed the apology was warranted, though not without some debate), and of the fact that I apologized (I confirmed it for him afterwards). But Zed doesn't owe me an update to his page, and I didn't ask for one. You, on the other hand, do bear an obligation to know what you're talking about before you try to use this incident in a public discussion. You obviously haven't lived up to that obligation.
I owe you no apology. My opinion about you isn't concealed and you aren't misunderstanding me. However, you are misrepresenting my comments by referring to them as "abusive" and threatening. Unless you're threatened by criticism of your rhetoric and of the technical quality of your project.
You've ignored all my attempts to make discussion with you constructive. You are nothing but a great big bully and you should feel shame for your behaviour.
Every time I comment about anything on HN, and every time I am personally mentioned or my work is mentioned, you dutifully pop up to do your work. It's disgusting. You have a problem with me and anyone who cares to look into this can deduce the same.
I am not threatened by technical criticism, but you simply go so above and beyond reasonable discourse thanks to your irrational, mentally unfounded conviction that everything I ever do or write is necessarily either the result of incompetence or bad faith. Between me and you, it seems you never find the room for nuance and human respect!
That's my final say regarding you. Your technical knowledge is amazing and I've learned a lot from you. But you make HN a terrible place with your personality.
* Requesting the crypto challenges and receiving some of them.
* Repeatedly asking me to talk to you privately, which, as you've acknowledged here in the least charitable way possible, I refuse to do. I respond to these requests simply and directly, without insult or explanation.
That's the extent of our correspondence.
As any reader of this thread can see, you and your work weren't "mentioned" on this thread. You're the manager of a project that competes with Whisper, and you chimed in on a thread about Whisper to ding them for something. I believed that ding was unfair and explained why. You then proceeded to --- if I may be permitted an uncharitable interpretation myself --- freak the hell out.
You should have just conceded the point (it turned out later in the thread that you were wrong to have brought it up). Instead, you relentlessly personalized it. Now you're unhappy with how that went for you. Maybe this can be a learning experience.
I was fine with the meta tangent we went off on earlier today, even though it didn't have that much to do with Whisper, because it did have something to do with forward secrecy, transcript consistency, and the relationship between protocols and their implementations. This, however has nothing to do with anything. The thread shows how this meta-tangent started: with me asking a technical question about your offering, and you giving a little speech about how bad a person I am.
We should probably wrap this up now.
My initial issue remains valid, and anyone who reads through the thread can see that you repeatedly attempted to change the focus to personalize this issue towards me. It's like I'm not allowed to offer any feedback, no matter how polite, constructive or valid, while you're around. Your doublethink is egregious.