Re: Monitor radiation overlooking.

[bgomes@netcom.com (Bill Gomes)]

Victor A. Borisov (blaster@rd.relcom.msk.su) writes:

> Some words about DES - I spoke with one cryptoanalisyst from
> KGB and he sow, that for number crypto algotitm c(key, text)
> (key is keyLength tall) present f(key, text), that for all
> key1 and key2 present key with length keyLength, that
> c(key2, c(key1, text))==f(key, text).

> He also say, that now present f() for c()=des(), more f() wery
> like des().

> That`s why for decrypting of des(k1, des(k2, ... des(kN, text) ... ))
> we must try 2^56 keys with spetial function.

And Lyle_Seaman@transarc.com replies:

> I had a little trouble with the English, but I think I followed the
> math.  I believe Victor's KGB friend is claiming that DES is a group. 
> Victor, does the following text contradict your claim?
> 
> (Excerpt from sci.crypt faq deleted)

I think that Victor's friend proposes a second function, f(), which is
not the same as DES.  He is saying that for every set of three keys
used for triple-DES (k2,k3,k4), there is a key (k1) such that:

        f(k1,text) = DES(k2,DES(k3, DES(k4,text)))

It seems to me this is different than saying DES is a group, since f != DES.

Am I mistaken?