Re: Wired query on Windows 2000 and DES/3DES

[Markku-Juhani Saarinen <mjos@cc.jyu.fi>]

> * 3DES is up to 10^17 (2^(112-56)) times as resistant as DES to an 
> exhaustive search. I assume that differential cryptanalysis cuts this 
> substantially, but I haven't been able to find any figures. I have come 
> across a related key attack that cuts total effort to 2^56 to 2^72, but I 
> understand this isn't practical.

Hi,

- Biham's related key attack [1] uses assumptions that do not hold in
  IPSec.

- Differential and linear cryptanalysis against 3DES requires more than
  2^64 known ciphertexts and can't work for that reason.

- The best attack (that I know of) is by Stefan Lucks [2]. He describes an
  attack that breaks 3DES in 2^108 steps. If you only count the single DES
  operations (and assume that memory access is fast etc) you only require
  2^90 of these. This is consistent with the overall IPSec security level.

[1] Eli Biham, "New Types of Cryptanalytic Attacks Using Related Keys,"
    Technical Report CS0753, Technion CS Department, 1992

[2] Stefan Lucks, "Attacking Triple Encryption," Proc. FSE'98, Springer
    LNCS series, 1998
    
Cheers,
- mj

Markku-Juhani O. Saarinen <mjos@jyu.fi>  University of Jyv”skyl”, Finland

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References:

• Wired query on Windows 2000 and DES/3DES
• From: Declan McCullagh <declan@well.com>

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