Subject: [dhcwg] Re: Authentication of DHCP Relay Agent Options Using IPsec

From: Michael Richardson <[email-masked]>
Date: Thu, 22 Sep 2005 14:27:00 -0400

>>>>> "Russ" == Russ Housley <[email-masked]> writes:
    Russ> The following document is on the agenda for the IESG telechat next
    Russ> week for approval as a Proposed Standard.  I would appreciate
    Russ> review from the members of this mail list in the next week.

    Russ>     Authentication of DHCP Relay Agent Options Using IPsec
    Russ> draft-ietf-dhc-relay-agent-ipsec-02.txt

  I think that I read this some time ago and commented about lack of clear
statement about how to do the keying.

  I have re-read it, and I still find the key management section too unclear:

>   Key management: Because the relay agents and servers are used within
>               an organization, public key schemes are not necessary.
>               Because the relay agents and servers must be manually
>               configured, manually configured key management may
>               suffice, but does not provide defense against replayed
>               messages.  Accordingly, if replay protection is required,
>               IKE [4] with preshared secrets must be used.  IKE with
>               public keys may be used.

  Are replays an issue? I think that threat model said clearly that they
were, so it seems to me that IKE "MUST" be used.

  I would like to see more clear statement about how to use IKE. In
particular, I think the DHCP relay agents are rather small boxes, and so the
full complexity of IKE is probably not desireable.

  My suggestions are:
     1) support IKE main mode only, and cookie-mode of IKEv2.

     2) support PSK authentication only. This works fine with MainMode
        in IKEv1 if your DHC relays are at known, non-changing addresses. 
        (If that isn't the case, please say so. I can think of situations
        where it might not be the case)

     3) I suggest modp1024 and modp1536 be supported. This is clearly easy
        to upgrade if you stick to mainmode, but if you decide you need
        aggressive mode, you have to pick one mode only.

     4) the relay does not need to support NAT-T, DPD, xauth, modecfg.

     5) in IKEv2, the relay does not need to support simultaneous SAs
        with the same selectors.

     6) phase 1 IDs of ID_IPV4_ADDR or ID_IPV6_ADDR will be supported.
        phase 2 IDs of ID_IPV4_ADDR (vs ID_IPV4_ADDR_RANGE with /32)
        will be supported. 

     7) You said transport mode already. Is fragmentation supported?
        Remember that the relay is adding stuff, and then you get to add
        ESP. 

     8) please recommend IKEv1 lifetimes, since they are not negotiated,
        and a mis-match still causes failure in many devices.
        (IKEv2 does not have this problem)

     9) The agent will support a PSK of between 16 and 64 bytes, and
        will accept hex (0x) and base64 (0s) encoded strings for entering
        the PSK in its' admin interface. This will encourage stronger PSKs
        and you won't find yourself in situation where you can only type
        a printable phrase.
        A 3-4 character hash of the PSK will be generated at each end to aid
        in confirming that the PSK has been entered correctly.
        
        I think that #6 is critical to specify if you actually want this
        security feature turned on during deployment.

-- 
]       ON HUMILITY: to err is human. To moo, bovine.           |  firewalls  [
]   Michael Richardson,    Xelerance Corporation, Ottawa, ON    |net architect[
] [email-masked]      http://www.sandelman.ottawa.on.ca/mcr/ |device driver[
] panic("Just another Debian GNU/Linux using, kernel hacking, security guy"); [
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From: "Van Aken Dirk" <[email-masked]>
Date: Mon, 26 Sep 2005 08:25:40 +0200

Hi Michael,

How do you come to the conclusion that DHCP relays are rather "small
boxes" and as a consequence don't need a full IKE implementation ?

As far as I know DHCP Relays are to be found in the complete range of IP
nodes which can range from very small to "huge".

Best regards - Dirk

> -----Original Message-----
> From: [email-masked] [mailto:[email-masked]] On Behalf
Of
> Michael Richardson
> Sent: donderdag 22 september 2005 20:27
> To: [email-masked]
> Cc: [email-masked]
> Subject: [dhcwg] Re: Authentication of DHCP Relay Agent Options Using
> IPsec
> 
> 
>     Russ> The following document is on the agenda for the IESG
telechat
> next
> particular, I think the DHCP relay agents are rather small boxes, and
so
> the
>         A 3-4 character hash of the PSK will be generated at each end
to
> aid
> ] [email-masked]      http://www.sandelman.ottawa.on.ca/mcr/
|device
> driver[