Erik Lindquist wrote: ] On Tue, 14 Mar 1995, Dr. Frederick B. Cohen wrote: ] ] > > In the tech notes that I have, it would seemt that RC2 uses a 128bit key and ] > > RC4 uses a 256bit key. ] > > ] > > Both these keys seem rather small in comparison to something like PGP's ] > > 1028bit key. ] > ] > 128bit key is about 40 digits - NSA approved - breakable by a PC ] > in a few hours. ] > FC ] > ] You have actually done this with a PC? With what kind of hw/sw??? ] Seems other comments would suggest that this would be an unlikely occurence. ] Can you expand on your statement. I cannot speak for Cohen, but *I* have factored 128-bit numbers in minutes, not hours, on a PC. Specifically, my 25MHz 386+387. A reasonable 486 Linux box could factor 70-digit integers in a few hours, using Lenstra and Manasse's PPMPQS code. I've never actually done such a thing on a 486, but I've factored many integers of about that size in a similar time on Sun 4/110 and DEC 5000/25 machines. I've factored numbers up to 104 digits (344 bits) using only my own resources and helped organize the factoring of the original RSA challange, a number of 129 digits or 426 bits. I have contributed to the factoring of a number of integers between 100 and 129 digits. With fairly good resources, but nothing exceptional, factoring 300-400 bit numbers is routine (but tedious!) these days. A 384-bit key can be broken in a few weeks with the idle time on the network of an average university department. For general purpose factorizations on MS-DOG machines, the UBASIC interpreter is the best I know. Library routines supplied with it provide ECM and MPQS algorithms for factoring moderate sized integers. My 386 could probably factor any integer of up to 80 digits with MPQS in a reasonable time (a few weeks) and can find 25 digit factors of integers up to a reasonable limit -- say 250 digits -- in the same time. Paul