[Hipsec] mm-03 CBA fixes

Returning to the mm draft comments from Miika.

> > 
> > > Figure 10.
> > 
> > Can the "+ address change" in the lower left corner be removed?
> > 
> 
> I will check with Christian about this figure, as your question has
> raised also a question in my mind whether it is correct.
> 

Christian has provided the following corrected figure.

        +-------+                        +-------+
        |   A   |                        |   B   |
        +-------+                        +-------+
            |                                |
    address |------------------------------->| credit += size(packet)
     ACTIVE |                                |
            |------------------------------->| credit += size(packet)
            |<-------------------------------| don't change credit
            |                                |
            + address change                 |
            + address verification starts    |
    address |<-------------------------------| credit -= size(packet)
 UNVERIFIED |------------------------------->| credit += size(packet)
            |<-------------------------------| credit -= size(packet)
            |                                |
            |<-------------------------------| credit -= size(packet)
            |                                X credit < size(packet)
            |                                | => do not send packet!
            + address verification concludes |
    address |                                |
     ACTIVE |<-------------------------------| don't change credit
            |                                |

             Figure 10: Readdressing Scenario

In the course of revising this, I discussed with Christian some
additional clarifying text and would like to propose the following text
that we worked out together:

- Section 3.3.2:  Add the following sentence right before the figure:

"Not shown in Figure 10 are the results of credit aging (Section
5.5.2), a mechanism used to dampen possible time-shifting attacks."

- Section 5.5:  At the beginning of this section (before reaching 5.5.1)
add:

"To prevent redirection-based flooding attacks, the use of
a Credit-Based Authorization (CBA) approach is mandatory when a host
sends data to an UNVERIFIED locator.  The following algorithm meets
the security considerations for prevention of amplification and
time-shifting attacks.  Other forms of credit aging--- and other values
for the CreditAgingFactor and CreditAgingInterval parameters in
particular--- are for further study, and so are the advanced CBA
techniques specified in [1]."

[1]
http://doc.tm.uka.de/2005/draft-vogt-mobopts-credit-based-authorization-
00.txt

(note to Christian:  This document [1] will need some official status or
republishing as a technical report)

- Section 6.  Add the following sentence just before starting Section
6.1:

"Security considerations for Credit-Based Authorization are discussed in
[2]."

[2]
http://doc.tm.uka.de/2006/draft-vogt-mobopts-simple-cba-00.txt

(note:  Christian says that he is working with Jari to publish this
draft)

Tom

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