Update core changelog.

core/CHANGELOG.md

@@ -1,3 +1,18 @@
+# 0.22.0 [unreleased]
+
+- Remove `PeerId` compatibility mode for "identity" and SHA2 hashes.
+  Historically, before 0.12, `PeerId`s were incorrectly always hashed with SHA2.
+  Starting from version 0.13, rust-libp2p accepted both hashed and non-hashed keys as
+  input.  Starting from version 0.16 rust-libp2p compared `PeerId`s of "identity" and
+  SHA2 hashes equal, which made it possible to connect through secio or noise to nodes
+  with an identity hash for the same peer ID. Starting from version 0.17, rust-libp2p
+  switched to not hashing the key (i.e. the correct behaviour) while retaining
+  equality between peer IDs using the "identity" hash and SHA2. Finally, with
+  this release, that will no longer be the case and it is assumed that peer IDs
+  whose length is less or equal to 42 bytes always use the "identity" hash so
+  two peer IDs are equal if and only if they use the same hash algorithm and
+  have the same hash digest.
+
 # 0.21.0 [2020-08-18]
 
 - Remove duplicates when performing address translation