On 10/19/14, 6:48 PM, Greg Troxel wrote:
Some of my friends have been moving away from XMPP/OTR to chat services that have centralized storage of plaintext (and proprietary software that only works on one platform, but that's not really relevant). While it's easy to criticize centralized plaintext, the usability issues are more complex. With the centralized plaintext service, one can continue chats across multiple devices, and move from computer to phone to tablet; turning on a device results in it connecting the serveer and getting the history. This has terrible security properties, but it's very handy. With xmpp, messages go to the current resource, more or less, so this history access doesn't work.
Not exactly. There are XMPP extensions (not yet universally implemented) to send messages to all resources and to store history on the server:
http://xmpp.org/extensions/xep-0280.html http://xmpp.org/extensions/xep-0313.html Naturally, it's best in that situation to run your own server.
With OTR, messages are encrypted to a particular xmpp client on one machine. That's a feature, really, in that there is no server plaintext, but it's also less usable. So, I wonder if it is time to think about how some new version of or improvements to xmpp and otr could result in a system that has the security properties of otr, more or less, and the usability properties of being able to continue across multiple devices. I wonder about having a server store more or less OTR ciphertext, but having each message encrypted to keys for all of a user's currently-set-up devices. One would lose integrity for off-line devices (when they connect and get old messages, the MAC keys would have been disclosed, so there's no guarantee they haven't been tampered with). But that seems like a small issue compared to now. One could argue that there's a loss of or risk of loss of confidentiality, due to multiple devices and keys. But it's much less Rthan the loss from using centralized plaintext storage.
Thanks for the interesting suggestions. Peter _______________________________________________ OTR-dev mailing list OTR-dev@lists.cypherpunks.ca http://lists.cypherpunks.ca/mailman/listinfo/otr-dev
