Losing the Code War by Stephen Budiansky

[Trei, Peter]

> marius[SMTP:marius.corbu at 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

---------------------------------------------------------------------
The Cryptography Mailing List
Unsubscribe by sending "unsubscribe cryptography" to majordomo at wasabisystems.com