Tree-creation with exceptions

[ineiti]

If we know a server is faulty, we could even say so when calling cosi.SignMsg so that the faulty server(s) are not included in the tree.

[nikkolasg]

If we know a server is faulty

How do you know if it is faulty ? By checking it first ? We should provide that as an option because it induces more latency to check every servers individually before doing the collective signing. Stg like --alive or --best . not good with names this morning >< What do you think ?

[ineiti]

I thought of taking the exception-bitmap of an old signature to chose which servers to use in the signature.

[nikkolasg]

From my point of view, the average use case for someone/software that needs to use CoSi is:

• try first the full set of witnesses
• if some do not reply, start again without the failed server
• Loop again if it still does not work

The question is largely how to know which server failed. For the moment, the node only know about their direct children / parent, but not about the whole topology in the tree. We need kind of a failure protocol so the root can re-start a round..

[jeffallen]

These are done in dedis/cothority.