Re: [dhcwg] more thoughts about draft-ietf-dhc-sedhcpv6-02.txt

[Francis Dupont <[e-mail]>]

 In your previous mail you wrote:

>  > => I can't see why you say that or do you mean timestamps have another
>  > role than anti-replay?
> My point is that giving the attacker the means to synchronise the
> replay attack with the target will give replay attacks a considerable
> time window in which to play.

=> synchronization allows to offer a smaller window.
I have two other arguments:
 - IMHO it is better to consider clients will be synchronize than
  to allow a large window and expect attackers to be never synchronized
 - it is clear timestamps by themselves are not enough, this is why
  I proposed to add nonces (note transaction IDs already provides
  24 bit of unpredictable data but 24 bits are not enough for high
  speed LANs)

> If signing messages in itself protects against replays, why bother
> with synchronising time?

=> signing is for origin and integrity, timestamps and/or nonces
are for anti-replay. Note it seems we need more analysis about
the usefulness of the anti-replay (I thought about the obvious
RELEASE replayed after a long delay but anyway a good security
threat analysis is (*again*) hardly needed... argh!)

Regards

[e-mail]