[10440] in cryptography@c2.net mail archive
RE: Losing the Code War by Stephen Budiansky
daemon@ATHENA.MIT.EDU (Trei, Peter)
Mon Feb 11 13:55:38 2002
Message-ID: <F504A8CEE925D411AF4A00508B8BE90A01E90C22@exna07.securitydynamics.com>
From: "Trei, Peter" <ptrei@rsasecurity.com>
To: Joshua Hill <josh@untruth.org>,
"'marius'" <marius.corbu@analog.com>
Cc: "'Ben Laurie'" <ben@algroup.co.uk>,
cryptography@wasabisystems.com
Date: Mon, 11 Feb 2002 10:21:36 -0500
MIME-Version: 1.0
Content-Type: text/plain
> marius[SMTP:marius.corbu@analog.com] wrote:
>
> > marius wrote:
> > > Not quite true. Encrypting each message twice would not increase the
> > > "effective" key size to 112 bits.
> > > There is an attack named "meet in the middle" which will make the
> > > effective key size to be just 63 bits.
> >
> > Peter Trei wrote:
> > > Don't forget that the MITM attack (which Schneier claims
> > > takes 2^(2n) = 2^112 time), also requires 2^56 blocks
> > > of storage.
> > [...]
> > > I don't lose sleep over MITM attacks on 3DES.
>
> 2^57 operations, with 2^56 blocks of storage manipulation can be
> approximated to: 2^56 * log(2^56) + 2^56 * log(2^56) = 2^62 + 2^62 =
> 2^63
>
> Betting on storage as a show stopper is not a good idea, regardless of
> sleep pattern.
>
> Marius
>
Oh, I totally agree - my first followup (Feb 4) read:
- start quote -
Either way, my point stands: any attack which requires 2^56 blocks
of storage is probably intractable for the time being, imho. 10 years
from now, I'm not so sure.
- end quote -
The expansion of storage over the last 20 years is even more
astonishing than the speedup of microprocessors. The first IBM
PC to ship with a HD (PC-XT ~1983) had a 5 Mb drive. When I
worked for Columbia U, undergraduates were given about 50kb
of diskquota for a semester.
Nevertheless, 2^56 blocks of centralized storage is a lot, and
will remain a lot for a while.
Peter Trei
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