TextSecure's Private Group Messaging
whispersystems.org
TextSecure's Private Group Messaging
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Re: TextSecure's Private Group Messaging
#2The 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 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.
That said, I strongly respect Open Whisper Systems. They usually release very well thought-out material. Perhaps they should have paid more attention though to this particular issue.
Re: TextSecure's Private Group Messaging
#3The 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…
They're not waving aside transcript consistency with their protocol, near as I can tell. ("We believe that it is possible to provide transcript consistency while preserving an asynchronous orientation.")
mpOTR, on the other hand, only shows transcript consistency at the end of a group chat session. This does seem problematic.
Re: TextSecure's Private Group Messaging
#4The 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…
They're not waving aside transcript consistency with their protocol, near as I can tell. ("We believe that it is possible to provide transcript consistency while preserving an asynchronous orientation.") mpOTR, on the other hand, only shows transcript consistency at the end of a group chat session. This does seem problematic.
Yes, per your quote, transcript consistency is discussed. But the discussion simply outlines problems with implementing it in their mobile use case — to my understanding the current version being offered to users doesn't have strong transcript consistency.
Re: TextSecure's Private Group Messaging
#5I've been using TextSecure for my private messaging and am a big fan.
I can't wait for WhisperSystems to release the iPhone version of the app -- at that point, all my family's communications will go through TextSecure.
Re: TextSecure's Private Group Messaging
#6The 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…
This post says that TextSecure implements transcript consistency in the protocol, and in a fashion objectively superior to that of mpOTR: the TextSecure protocol can provide continuous consistency checks, while mpOTR can do so only when the session is torn down. What the TextSecure client does not yet do is provide a UI for that feature of the protocol.
Further, it's hard to understand how transcript consistency could be a serious objection while lack of forward secrecy in the messages isn't, especially given the deniable messaging semantics of OTR.
So, to address your concluding sentence directly: it seems to me like Moxie has paid more attention to this issue than you have.
Re: TextSecure's Private Group Messaging
#7The 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…
This post says that TextSecure implements transcript consistency in the protocol, and in a fashion objectively superior to that of mpOTR: the TextSecure protocol can provide continuous consistency checks, while mpOTR can do so only when the session is torn down. What the TextSecure client does not yet do is provide a UI for that feature of the protocol. Further, it's hard to understand how transcript consistency coul…
I'm quite certain that the current TextSecure chat allows my proposed scenario with Alice, Bob and Carol to go through without issue. This is the main problem here. So while transcript consistency is discussed in the blog post, it remains the case that Alice can send a different message to Bob and Carol without being detected.
Re: TextSecure's Private Group Messaging
#8" ephemeral signing key pair along with K. ... hash-ratcheting K and including a signature in the transmitted ciphertext."
Can someone knowledgable comment about the crypto protocol here and how this provides guarantees that ensure the server can't reverse the messages for multicast (am happy to read academic papers here too)?
Re: TextSecure's Private Group Messaging
#9Earlier quoted context omitted.
This post says that TextSecure implements transcript consistency in the protocol, and in a fashion objectively superior to that of mpOTR: the TextSecure protocol can provide continuous consistency checks, while mpOTR can do so only when the session is torn down. What the TextSecure client does not yet do is provide a UI for that feature of the protocol. Further, it's hard to understand how transcript consistency coul…
I'm quite certain that the current TextSecure chat allows my proposed scenario with Alice, Bob and Carol to go through without issue. This is the main problem here. So while transcript consistency is discussed in the blog post, it remains the case that Alice can send a different message to Bob and Carol without being detected.
This is a comment you could have written without even reading my comment. You haven't responded to anything I just wrote. I'm not surprised; your function in TextSecure threads seems to be to pop out and complain about TextSecure without mentioning that you're the author of Cryptocat, a competing (and inferior) offering.
Re: TextSecure's Private Group Messaging
#10Earlier quoted context omitted.
I'm quite certain that the current TextSecure chat allows my proposed scenario with Alice, Bob and Carol to go through without issue. This is the main problem here. So while transcript consistency is discussed in the blog post, it remains the case that Alice can send a different message to Bob and Carol without being detected.
This is a comment you could have written without even reading my comment. You haven't responded to anything I just wrote. I'm not surprised; your function in TextSecure threads seems to be to pop out and complain about TextSecure without mentioning that you're the author of Cryptocat, a competing (and inferior) offering.
I think TextSecure is an excellent and inspiring project. All I'm trying to do is identify an area of concern for me. I'm not sure why you're attacking me personally here. I think my initial point of concern stands and I hope the TextSecure developers will work on addressing it.
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.