Changes file for feature 15056 (prop220, extend cell side)

changes/feature15056

@@ -0,0 +1,28 @@
+  o Major features (ed25519 identity keys):
+    - Relays now understand requests to extend to other relays
+      by their Ed25519 identity keys. When an Ed25519 identity key
+      is included in an EXTEND2 cell, the relay will only extend
+      the circuit if the other relay can prove ownership of that identity.
+      Implements part of ticket 15056; part of proposal 220.
+    - Clients now support including Ed25519 identity keys in the EXTEND2
+      cells they generate.  By default, this is controlled by a consensus
+      parameter, currently disabled.  You can turn this feature on for
+      testing by setting ExtendByEd25519ID in your configuration. This might
+      make your traffic appear different than the traffic generated by other
+      users, however.
+      Implements part of ticket 15056; part of proposal 220.
+
+  o Code simplification and refactoring:
+    - The code to generate and parse EXTEND and EXTEND2 cells has
+      been replaced with code automatically generated by the "trunnel"
+      utility.
+    - Remove data structures that were used to index or_connection objects by
+      their RSA identity digests. These structures are fully redundant with
+      the similar structures used in the channel abstraction.
+
+  o Minor features (directory authority):
+    - Add a new authority-only AuthDirTestEd25519LinkKeys option (on by
+      default) to control whether authorities should try to probe relays by
+      their Ed25519 link keys.  This option will go away in a few
+      releases--unless we encounter major trouble in our ed25519 link
+      protocol rollout, in which case it will serve as a safety option.