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Re: ipsec error protocol



To repeat a previous suggestion I made to this list last year:

   If we have the system sign a "birth certificate" when it reboots
   (including a reboot time or boot sequence number), we could include
   that with a "bad spi" ICMP error and in the negotiation of the IKE SA.

   This pushes the burden of reestablishing state to the end which
   already thinks it has shared state and has traffic it wants to send.

   The system which is receiving packets to unknown SPI's merely has to
   respond with a simple message which involves no real-time cryptography
   (it should, of course, be rate limited).

   The system receiving the error message can discard it if it doesn't
   correspond to existing state or if it's "old news" (i.e., you get
   replay protection); if it's not old news, you can rate-limit how often
   you attempt to verify the signature.

I think that, in practice, a boot sequence number will suffice and
require minimal state.  Also, the "birth certificate" could be
included in an "unknown phase 1" IKE error, to allow for faster
recovery from loss of phase 1 state..

					- Bill


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