1) At registration time, a client generates a random ID and
transmits to the the server.
2) The server provides that registration ID to any client
that requests a prekey.
3) Clients include that registration ID in any
PreKeyWhisperMessage.
4) Clients include that registration ID in their sendMessage
API call to the server.
5) The server verifies that the registration ID included in
an API call is the same as the current registration ID
for the destination device. Otherwise, it notifies the
sender that their session is stale.
1) In addition to the Recipient interface, there is now
RecipientDevice. A Recipient can have multiple corresponding
RecipientDevices. All addressing is done to a Recipient, but
crypto sessions and transport delivery are done to
RecipientDevice.
2) The Push transport handles the discovery and session setup
of additional Recipient devices.
3) Some internal rejiggering of Groups.
1) Added SMS transport support.
2) Keep track of whether a PreKeyBundle message has gotten
a response, and send them as subsequent messages until
one has been received.
1) Move all the crypto classes from securesms.crypto.
2) Move all the crypto storage from securesms.database.keys
3) Replace the old imported BC code with spongycastle.
