Subject: [mobile-ip] Home and COA cookie generation

From: Samita Chakrabarti <[email-masked]>
Date: Thu, 15 Aug 2002 18:48:16 -0700 (PDT)

Section 5.2.5 of draft 18, specifies the following algorithm  for
home cookie and coa cookie:

  home cookie = First64(MAC_Kcn(home address | nonce))
  
  care-of cookie = First64(MAC_Kcn(care-of address | nonce))

  Previously,  (draft 16) talked about concatanating 0 and 1 for
  home cookie and care-of cookie, i.e:
  home cookie = MAC_Kcn (home_address | nonce| 0)
  coa cookie  = MAC_Kcn (coa_address | nonce | 1)
  
  Have we decided not use 0 and 1 any more to distinguish the cookies ?
  
  Thanks,
  -Samita

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From: Vladislav Yasevich <[email-masked]>
Date: Fri, 16 Aug 2002 10:10:01 -0400

Hi Samita

Why would you need to distinguish the cookies like this?

-vlad

-- 
+++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++
Vladislav Yasevich	       Tru64 UNIX - IPv6 Project Lead
Hewlett Packard 	       Tel: (603) 884-1079
Nashua, NH 03062	       ZKO3-3/T07

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From: Jari Arkko <[email-masked]>
Date: Mon, 19 Aug 2002 11:45:41 +0300

Samita Chakrabarti wrote:
>   home cookie = First64(MAC_Kcn(home address | nonce)

The rules have been simplified in draft 18. There does not
seem to be any advantage in making the cookies truly different
this way. (A long time ago we debated whether the cookies must
depend on both addresses, but that was another issue.)

The inclusion of the 0 or 1 in the input of the MAC has the
effect of requiring the MN to use specifically the Home Test
and the Care-of Test messages to retrieve the corresponding
cookies. If these values are not included, an attacker could
use the value acquired through a Care-of Test message as a
home cookie. However, this does not appear to make the life
of the attacker any easier; if the attacker can send a particular
MH message then he can most likely send another MH message as
well. Obviously, the cookies are still dependent on the addresses
so the attacker can't get a home cookie without being able to
receive traffic at the home address.

Tuomas or Mike may comment on this, as the values were included
in BAKE/2. My proposal is to not include the values unless we
have an explicit reason to do so.

Jari