o Group Diffie-Hellman protocol for establishig key with two or more
users on a channel.
+ o Define that with CTR mode PFS MUST be enabled in SKE. CTR rekey
+ cannot be done without PFS because the counter block requires fresh
+ HASH value which requires PFS in rekey.
+
o Extend the Channel ID port to be actually a counter, allowing the
2^32 channels per cell, instead of 2^16 like now. The port with
compliant implementation would always be 706, and it could be used