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nextleap-project / countermitm

thoughts on countering mitm-attacks on autocrypt
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Build verified group based on verified contacts rather than having two sligtly different protocols #67

Closed azul closed 5 years ago

azul commented 6 years ago

Part of the follow up on messaging list feedback (#61):

In https://moderncrypto.org/mail-archive/messaging/2018/002541.html Bryan commented:

In general, I’m not seeing why it’s either necessary or desirable to “roll together” the pairwise (Alice-Bob) verification workflow with the verified group-join protocol, instead of making them properly-linked but separate activities. As currently designed, the protocol seems to make it fundamentally necessary for Alice and Bob go through the rigmarole of person-to-person device verification each time Alice wants to invite Bob to a new verified group or vice versa. If Alice and Bob are longtime friends, which I expect and hope will be the common case especially for the most sensitive verified groups, then it seems more likely that Alice and Bob will likely already have a relationship verified via person-to-person secure connect (section 2.1), and just want to reuse or refer to that when one of them wants to invite the other to join a verified group.

In fact, the current rolled-together process seems like it’s optimized for, and perhaps even incentivizes, the less-secure behavior of inviting people to sensitive groups on first meeting them. Suppose Alice meets Bob in-person at a meeting or party, for example, and let me try to channel Alice’s potential thought process: “Hmmm, Bob seems interested in that topic that might make him a good potential member for this sensitive group I’m in… But I just met him and don’t know him very well yet; I wonder if I should hold off on inviting him and first ask around to see if anyone else knows anything good or bad about him? Oh crap, no, if I do that then Autocrypt is going to insist that I re-run that device connect rigmarole and re-verify him later once I decide to invite him to the group, and by then I’ll be back in Foozloo. So @#$% security, I’ll just chance it and invite him to the group now.” Maybe not really the user behavior we want to be incentivizing?

hpk42 commented 5 years ago

I think with the recent PR merges we addressed this issue already. The switch of terminology to "second channels" also leads away from the "device-to-device" physical vicinity ... maybe it's good to make it clearer that "verifications" are supposed to not only happen for very sensitive groups but as part of everyday-getting-in-contact? (especially with the "setup contact" protocol which allows two people to get a chat channelw ith each other without having to type phone numbers or email addressees).