[whispersystems] TextSecure version 3

[Sebastian Verschoor]

Hello,

It appears that the Axolotl protocol is at version 3, but I can find no
documentation on what has changed since version 2 of the protocol?

I am trying to understand the function of:

1. The signed prekey
2. The last resort key (this might already have been there in v2)

Can you point me at the documentation?

Thanks,
Sebastian