Re: [MLS] *re*joining a group with the same identity key

[Jon Millican <[e-mail]>]

One potential option that comes to mind is for the server to help it reinsert itself in the correct place. This would essentially amount to a join, but serving its own copath instead of the group’s frontier. We could then reject somebody double-joining their own identity key; under the assumption that this could only happen with a malicious server anyway.

I don’t have strong feelings about this vs your proposed solution though. The main benefit would probably be just in terms of keeping the tree cleaner and minimising remove operations that need to be done.

Jon

On 25/07/2018, 12:01, "MLS on behalf of Katriel Cohn-Gordon" <[e-mail]<mailto:[e-mail]> on behalf of [e-mail]<mailto:[e-mail]>> wrote:

Hi all,

Here'a s case we might want to think about: what should happen if a current member of a group asks to join, with the same long-term key that they're already joined with?

The simple answer is to forbid such joins, but this might happen if a device forgets its group state but remembers its identity key. (Perhaps it writes the group state to a local database and the write got corrupted.)

Alternatively I see a handful of different ways we could support these joins, if we wanted to. Perhaps the simplest is to allow the device to double-join but require it to immediately delete the old copy of itself.

best,
k