Re: Slicing and dicing

"Michael C. Richardson" <mcr@sandelman.ottawa.on.ca> Fri, 12 September 1997 17:34 UTC

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Subject: Re: Slicing and dicing
In-reply-to: Your message of "Fri, 12 Sep 1997 12:35:56 EDT." <199709121635.MAA05295@dcl.MIT.EDU>
Date: Fri, 12 Sep 1997 13:47:35 -0400
From: "Michael C. Richardson" <mcr@sandelman.ottawa.on.ca>
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>>>>> "Theodore" == Theodore Y Ts'o <tytso@MIT.EDU> writes:
    Theodore> Note that this is also only a problem if we some how end
    Theodore> up re-encrypting the encrypted packet again, such as in
    Theodore> applications where you might be using two layers of ESP
    Theodore> for some reason.  In those cases, the probability of
    Theodore> trouble would be (20 * 2**-56 * 2**-56 * 20**-64), or
    Theodore> (20 * 2**-176), or 2 * 10**-52.

  Given this, I'd say forget about handling it.
  The world isn't just DES, though. The question about what to do with
weak keys in general. Are weak keys in other algorithms equally
improbable? 

  Given the difficulty in even test code to replace the weak keys with
other keys, I'd prefer to simply fail the SA, and cause ISAKMP to
start over again. I think even my vic-20 can afford to do this once
every (86400/300 * 365)/(2* 10**-52) years. 

   :!mcr!:            |  Network security programming, currently
   Michael Richardson | on contract with DataFellows F-Secure IPSec
 WWW: <A HREF="http://www.sandelman.ottawa.on.ca/People/Michael_Richardson/Bio.html">mcr@sandelman.ottawa.on.ca</A>. PGP key available.




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