From: Karl Lui Barrus <klbarrus@owlnet.rice.edu>
Date: Sat, 30 Oct 93 08:53:27 PDT
To: cypherpunks@toad.com
Subject: Re: Paranoid
Message-ID: <9310301553.AA00702@elf.owlnet.rice.edu>
MIME-Version: 1.0
Content-Type: text/plain


-----BEGIN PGP SIGNED MESSAGE-----

I'm not exactly sure what this thread is about :-) but I do have some
numbers:

Differential cryptanalysis of DES requires 2^47 = 140737488355328 =
1.4 10^14 known plaintexts.

The complexity of a brute force DES attack (keysearch) is 2^56 =
72057594037927936 = 7.2 10^16, or 2^55 = 36028797018963968 = 3.6 10^16
if you are efficient.

Similary, brute forcing IDEA is 2^128 =
340282366920938463463374607431768211456 = 3.4 10^38

The best factoring algorithm (gopher plug: check in Misc/ for
a recent "bits and difficulty factoring post") for a 1024 bit key is 
a complexity of 4.42 10^29.

Somewhere around 1600 bits comes a point where it is "easier" to
attack IDEA than factor the resulting number.

Karl Barrus
<klbarrus@owlnet.rice.edu>

-----BEGIN PGP SIGNATURE-----
Version: 2.3a

iQCVAgUBLNKNqYOA7OpLWtYzAQFlkwP+PdenJNJOKm9zcxkL4Zaq22aujfa2SAgk
1NILjQzZI8uZe9FIn8p2uEoS3YjYskg40tEMeohhGqZ371s/ndlTjDDhga0PCXLj
Q4UHoowTVR9hx/cVGzLhuZbyAwbbqAvygGQNKN1iXn3IqpLoNV3Do+TtUj0xLt1l
0j1gl055YL4=
=Vl2r
-----END PGP SIGNATURE-----