[Hipsec] a state machine proposal for mm-03

[Miika Komu <[e-mail]>]

Simplified State Machine without Peer Initiated Rekeying
========================================================

Note1: since there are no other HIP header types for mobility and
multihoming (other than UPDATE), the actual packet processing depends
on the parameters in the HIP packet.

Note2: the state machine is simpler to design if we leave out the peer
initiated rekeying (section 3.2.1.2 in the draft). This way, we can
assume that the UPDATE exchange consists of three packets and that
each packet can be distinguished from each other by the precence of
LOCATOR, ECHO_REQUEST or ECHO_RESPONSE.

Note3: reusing the same state variables on both hosts. At the mobile
host (the sender of LOCATOR) it is related to the data structures of
the source IP. On the corresponding node (receiver of LOCATOR), it is
related to the destination IP.

Note4: need some fresh eyes to verify that this is actually sensible :)

Send UPDATE with LOCATOR:
  - Triggered at the MN depending on changes in network attachments
    and according to local policies
  - Removed addresses are DEPRACATED (and not included in the
    LOCATOR)
  - All other addresses are UNVERIFIED (and included in the LOCATOR)
  - Set preferred LOCATOR depending on local policies
  - Send UPDATE with LOCATOR for the CN

Receive HIP UPDATE:
- Verify the HIP packet: HMAC, SIG, the presence, dependencies and
  validity of the parameters.
  - If the result is failure, goto DROP.
  - If success, proceed based on presence of LOCATOR, ECHO_REQUEST or
    ECHO_RESPONSE (only one of them can be contained in the packet)

Received LOCATOR:
- For each MN address in the received LOCATOR
  - State is DEPRACATED or UNKNOWN
    - Goto UNVERIFIED and send ECHO_REQUEST
  - State is UNVERIFIED
    - Resend ECHO_REQUEST and decrease retransmission timeout
  - Any other state, DROP

Received ECHO REQUEST:
- For each MN address in the corresponding LOCATOR
  - State is UNVERIFIED
    - Goto ACTIVE and send ECHO_RESPONSE
  - Any other state, DROP

Received ECHO_RESPONSE:
- Goto DEPRACATED for all old addresses not present in LOCATOR
- For each MN address in the corresponding LOCATOR
  - State is UNVERIFIED
    - Otherwise goto ACTIVE
    - Change preferred LOCATOR when necessary
  - Any other state, DROP

Receive ESP:
- For the ESP address
  - State is UNVERIFIED
    - Verify ESP validity. Goto DROP if failed
    - Change preferred LOCATOR when necessary
    - Process ESP if there are credits left, and decrease credits.
    - Otherwise DROP
  - State is ACTIVE
    - Process ESP
  - Any other state, DROP

Send ESP:
  - Increase credits

UPDATE retransmission timeout for LOCATOR (at MN):
  - State is UNVERIFIED
    - Resend and decrease retransmission counter
  - Any other state
    - DROP and zero retransmission counter

UPDATE retransmission timeout for ECHO_REQUEST (at CN):
  - State is UNVERIFIED
    - Resend and decrease retransmission counter
  - Any other state
    - DROP and zero retransmission counter

UPDATE retransmission timeout for ECHO_RESPONSE (occurs at the MN when no
ESP was received from the CN from a new address?):
  - State is ACTIVE
    - Resend and decrease retransmission counter
  - Any other state
    - DROP and zero retransmission counter

Handling of CLOSE with ESP_INFO:
- TBD

-- 
Miika Komu              [e-mail]          http://www.iki.fi/miika/

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