Re: New SPI when renegotiate keys?

[Bill Sommerfeld <sommerfeld@apollo.hp.com>]

> > If so, why?
> 
> Because IP has no delivery guarantees, and changing the keys on an existing
> SA will scramble packets that arrive AFTER the rekeying, but were
> encrypted/authenticated BEFORE the rekeying.  Hey, it's IP, anything can
> happen.
> 
> Consider the following SA:
> 
> 	A -> B, AH HMAC-MD5, SPI = 0x84001100, key = <foo>
> 
> So I receive some packets for SA {B, 0x84001100}.  Suddenly I perform an
> ISAKMP regnegotiation and change the key from <foo> to <bar>.
> 
> But say before that happened, a packet left A.  Let's say that the packet got
> caught in a routing loop while the ISAKMP exchange took place.  Suddenly this
> old packet arrives at B, and the SA lookup succeeds.  But now, the key is
> different so it won't authenticate.

I agree 100% with this analysis..

In addition, I believe that most if not all significant properties of
SA's need to be "immutable".. because any changes to SA's might be
reordered around traffic to/from them..

					- Bill

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References:

• Re: New SPI when renegotiate keys?
• From: Dan.McDonald@eng.sun.com (Dan McDonald)

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