Composing large block cipher from smaller ones
in [Cryptography]
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From: J.D. on 6 Mar 2010 15:21 > As layman... You know, there's a cure for your condition. And it doesn't involve laying in bed, asking us to spoon-feed you for the rest of your life...
From: Mok-Kong Shen on 6 Mar 2010 15:31 [Sorry, my previous post was not complete.] Maaartin wrote: > Mok-Kong Shenwrote: >> DES was first raised in this thread not by me but by Maaartin. > > You're wrong, it was you ("I have omitted the swapping operation that > is present e.g. in DES, for that's irrelevant for security, if I > don't err."). Apology, I was wrong. >> You >> may be right in not (indirectly) 'propagating' DES, though on the other >> hand I am not clear of how 'only slightly longer' could be >> substantially argued. > > Quite obvious: DES has only 56 bit key, and you're going to us it in > CTR more. So where is the problem, just try all the keys. The point argued was whether to crack the "composite" ciphe, consiting of u DES, needs "only slightly longer" than cracking one single DES. As I said, that needs at least u times at much work. (In the now revised version, one uses u DESs, that from u keys generate the keys for the corresponding component DESs in the diverse rounds.) M. K. Shen
From: J.D. on 6 Mar 2010 15:35 > > Quite obvious: DES has only 56 bit key, and you're going to us it in > > CTR more. So where is the problem, just try all the keys. > > The point argued was whether to crack the "composite" ciphe, consiting > of u DES, needs "only slightly longer" than cracking one single DES. > As I said, that needs at least u times at much work. (In the now > revised version, one uses u DESs, that from u keys generate the keys > for the corresponding component DESs in the diverse rounds.) > > M. K. Shen That's exactly the version he was talking about. Does this really need to be spelled out for you even more clearly?
From: Mok-Kong Shen on 6 Mar 2010 15:38 Am 06.03.2010 21:21, schrieb J.D.: >> As layman... > > You know, there's a cure for your condition. And it doesn't involve > laying in bed, asking us to spoon-feed you for the rest of your > life... Should I behave like a few of others in this group in always attempting to (undeservedly) present oneself as an 'expert'? If you have concrete 'objective' scientific arguments, then please argue. But to do personal attacks unnecessarily wastes the bandwidth of the group and is a very 'mean' conduct in my personal view. M. K. Shen ------------------------------------------------------------------------ [A second time:] My favourite citation for scientific discussions: Was sich ueberhaupt sagen laesst, laesst sich klar sagen; und wovon man nicht sprechen kann, darueber muss man schweigen. L. Wittgenstein
From: Mok-Kong Shen on 6 Mar 2010 15:41
J.D. wrote: >>> Quite obvious: DES has only 56 bit key, and you're going to us it in >>> CTR more. So where is the problem, just try all the keys. >> >> The point argued was whether to crack the "composite" ciphe, consiting >> of u DES, needs "only slightly longer" than cracking one single DES. >> As I said, that needs at least u times at much work. (In the now >> revised version, one uses u DESs, that from u keys generate the keys >> for the corresponding component DESs in the diverse rounds.) > That's exactly the version he was talking about. Does this really > need to be spelled out for you even more clearly? So where is the foundation of "your" 'only slightly longer'?? We were talking about the entire composite cipher! M. K. Shen |