Re: Nortel CES (3DES version) offers false sense of security when usi ng IPSEC

[Rogier Wolff <R.E.Wolff () BITWIZARD NL>]

spitko () HOTMAIL COM wrote:
> CES 1510D; D stands for domestic == 128 bits version). For some reason
> stickers on shipping package says 128 bit encryption and documentation
> states 168 bits (== 3*56 bits DES) encryption.

I don't know where people get their information, but tripple-DES uses
a 112 bit key. How they can advertize 128, or even 168 bits of keys I
don't know.

Triple DES is triple because you run the plaintext through DES three
times, however you use only two different keys.

Why? There is a "meet in the middle" approach that allows you to figure
out the keys on a "triple-DES-with-three-keys" in a brute-force attack
of complexity 2^112. (*)

So even if they don't do the standard triple-DES with two keys, they
should only claim 112bit security, not one bit more.

Now this "meet in the middle" attack is over my head. I haven't the
foggiest how one would go about this. And it's been over 10 years
since I last took a cryptography class. So, better trust the experts
on this than me.

                        Roger.

(*) Remember a few years ago, some guys from Israel managed to "break"
single-DES with a meet-in-the-middle attack. Turns out their attack is
of complexity 2^56 (or thereabouts), even if the original DES would've
used a 64 bit key instead of the 56bit key in the standard.


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