http://zzzmirror.i2p/posts/15212
(Also, FYI, it's one of the two "ratchets" in our "double ratchet" scheme taken from Signal). No protocol changes were required. With both of our ratchets now working, transfers over 100 MB total between two peers should now work, even between Java i2p and i2pd. We also today went through the other unimplemented blocks and declared them optional for now.