Dear tor relay operators,
we want to inform you that in future*, tor directory authorities will enforce a new security measurement that disallows relays to drop Ed25519 support in case they ever supported it at some point.
In practice that means that if you run tor 0.2.7.2-alpha or later you can not downgrade to an older tor version without Ed25519 support anymore. Tor directory authorities will reject such relays in the future.
You are safe if you do _not_ downgrade from any tor version >= 0.2.7.2-alpha to a version older than that.
We will send a second email to this list once we are near the actual enforcement of this new requirement (which will not be to soon from now).
kind regards, nusenu
* This will come into effect when the majority of tor directory authorities are on tor 0.3.4.x
ticket: https://trac.torproject.org/projects/tor/ticket/20522