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RE: How to negotiate key length with ISAKMP?
Blowfish has a variable length key up to 448. Just throwing it out there, I know
people don't want to hear it because "Blowfish hasn't been tested." However....
In any case, there is a difference between the length of the key used for a
particular algorithm and the length of the keying material required.. Here we are at
slicing and dicing again.
I've haven't been following the discussion much lately due to some overwhelming
commitments.. In any case, were are we on the slicing and dicing issue. I
know there were concerns about entropy which I don't think were resolved.
Please forgive if any of my comments are counter to a resolution to slicing
and dicing made in this group. And if my comments are counter, could someone
please post the solution/resolution???
If we are allowing the IPSEC algorithms themselves to do the slicing and
dicing, then one big slab o' keying material should be negotiated by ISAKMP.
The IPSEC algorithm should be able to suggest its desired key length and
ISAKMP should provide a hunk of keying material of the requested size or
larger. How the keying material is used by IPSEC is irrelevant no? Whether it
be a variable length Blowfish key plus a key to do HMAC SHA with or simply
a 128 bit MD5 key doesn't matter, does it?
From: Michael C. Richardson [SMTP:firstname.lastname@example.org]
Sent: Monday, June 23, 1997 3:29 PM
Subject: Re: How to negotiate key length with ISAKMP?
>>>>> "Perry" == Perry E Metzger <email@example.com> writes:
Perry> Not to say that you aren't right about needing to negotiate
Perry> key lengths in general, and certainly with RC4 and RC5, but
Perry> I believe CAST-64 and CAST-128 are really different
Perry> algorithms, not a single algorithm with a variable sized
Perry> key length.
But, are we really going to want 76 bit and 72 bit rc4? I think
there might be three, maybe four key sizes, and that is it. I know
that there are two: 40 bit and 128 bit. Are there really more?
I think that algorithms of differing key sizes are as different from
a policy point of view as different algorithms.
:!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">firstname.lastname@example.org</A>. PGP key available.