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Re: key change for TCP-MD5
- From: Steven M. Bellovin
- Date: Mon Jun 26 20:44:53 2006
On Tue, 20 Jun 2006 17:06:27 -0400, Ross Callon <email@example.com>
> At 12:12 PM 6/20/2006 -0700, Bora Akyol wrote:
> >The draft allows you to have a set of keys in your keychain and
> >the implementation tries all of them before declaring the segment
> >as invalid.
> DoS against routers is of course a major concern. Using
> encryption has the potential of making DoS worse, in the
> sense that the amount of processing that a bogus packet
> can cause is increased by the amount of processing
> needed to check the authentication. If the router needs to
> check multiple keys in the keychain before declaring the
> segment as invalid, then this multiplies the effect of the
> DOS by the number of keys that need to be checked.
You're quite right, and the next version of the draft contains the
following additional text in the Security Considerations:
Having multiple keys makes CPU denial of service
attacks easier. This suggests that keeping the
overlap period reasonably
short is a good idea. In
addition, the Generalized TTL Security Mechanism
<xref target="RFC3682" />, if applicable to
the local topology, can help.
Note that there would almost never be more than
two keys in existence at any one time in any event.
--Steven M. Bellovin, http://www.cs.columbia.edu/~smb