From: John Payson Subject: Re: 2x Isolated Double-DES: Another Weak Date: 21 Feb 1994 12:31:02 -0600 Organization: /usr/lib/news/organi[sz]ation Lines: 25 NNTP-Posting-Host: mercury.mcs.com In article <9402192242594.davesparks.DLITE@delphi.com>, Dave Sparkswrote: > >> This works for the normal double-DES construction because it is > >> possible to check for matches between B and C; the weakness seems > >> to be the ability to check for a match. > >How would this be implemented? Wouldn't you have to keep all of your Bs and >Cs in active memory, and perform a comparison each time? This could total as >many as 2^56 of each, correct? Not only would each have to be kept in >memory, but as the search progressed, the number of comparisons would >increase each time. I suppose you could keep the list of intermediate B and >C values in a sorted array and do a binary search each time, but it still >seems quite memory-intensive. By my calculations, 2^60 bytes of >storage would be needed. Am I missing some optimization that would make this >sort of an attack practical? Yes. Given two lists of numbers in which you would like to find duplicates, all you need to do is SORT the lists of numbers; then the time to do a matchup is linear in the size of the lists. While your tape (I can't really see using any other kind of I/O) would have to be really huge, it would probably not be impossible. -- ------------------------------------------------------------------------------- supercat@mcs.com | "Je crois que je ne vais jamais voir... | J\_/L John Payson | Un animal si beau qu'un chat." | ( o o )