-----BEGIN PGP SIGNED MESSAGE----- There should be a new version of PGP Tools and Magic Money on csn.org soon. The PGP Tools will be called pgptl10b.zip and the Magic Money will be mgmny10b.zip. The new naming was warlord's idea: the "b" will be "c" etc in future releases, until some serious updating justifies a new version. The new Magic Money does not contain the PGP Tools files, so be sure to download PGP Tools as well. Will I run out of bugs or letters first? :-) The prime-multiplication problem appears to have gone away. The new Magic Money checks the whole coin, but the attack is probably impossible anyway. jkreznar@ininx.com quotes: Here we consider only {\em prime\/} divisors of $n$ and ask, for given order of magnitude of $n$. ``how many prime divisors are there typically?'' and ``how many {\em different\/} ones are there?'' Some of the answers will be rather counterintuitive. Thus, a 50-digit number ($10^{21}$ times the age of our universe measured in picoseconds) has only about 5 different prime factors on average and --- even more surprisingly --- 50-digit numbers have typically fewer than 6 prime factors in all, even counting repeated occurrences of the same prime factor as separate factors. We will also learn something about the distribution of the number of prime factors and its implications for the important factoring problem. Thus, we discover that even for numbers as large as $10^{50}$, the two smallest primes, 2 and 3, account for about 25\% of all prime factors! A number of several hundred digits, such as a Magic Money coin, if it were to be made of all small primes, would need 50 or 100 factors. These would probably be very rare, considering this average. hfinney@shell.portal.com wrote:
I was thinking over the attack I described on Magic Money and Chaum cash, and I now think it will not actually work, especially in the case of the Chaum cash. Specifically, it will take as much work to forge cash as to factor the modulus.
[ describes how finding smooth numbers is equivalent to factoring ]
So, unless there is in fact some trick that can be used to quickly find smooth numbers given that the low order 128 bits are free, I don't think there is any need to worry about my attack on Magic Money. And it looks like Chaum's online cash is completely invulnerable to this approach.
Unless something else comes up, it looks like we don't need to worry about this one. If it does become a problem, it would be easy to go to full Chaum cash - take the MD5 of a random number and use it, including the random number in the coin. But there is no reason to code this unless we find out we need it. As for the big-endian problem, andrewl@wtg20.wiltel.com wrote:
I retrieved the latest version of Magic Money from the mpj archive and compiled it on a big-endian machine (a 68k NeXT). It seems to work now... I was able to setup the server and client and move a little cash around whereas before the server would never sucessfully find a q....
This was the last version, which set all precision to max. The last version also had a bug in pgp_extract_rsa, again involving set_precision. The new one has defines which try to use lower precision and adjust pointers, for those functions which can be sped up this way. If that fails, another define will go back to setting everything max. Please test this on a big-endian machine and find out if it works without everything set to max. If it doesn't, please try to debug it and post what needs to be done. The code seems to be getting close to working. Does anyone want to set up a Magic Money server? You could run it through a remailer, if you want to. The server filters PGP messages from stdin to stdout, so you would not need root access to run one. It would probably be no harder than running a remailer. I compiled in the 8086.asm under DOS, and it is fast enough. Use the assembly for whatever system you are running on, because the server has to perform a lot of secret key operations: decrypt, sign message, and sign each coin. Pr0duct Cypher -----BEGIN PGP SIGNATURE----- Version: 2.3a iQCVAgUBLVdKTsGoFIWXVYodAQFGAgQAgNs7PiGe3KItFiouUs/iXoH5bfVsgdGs pVbf4sTZcF3c531KARJGxVkXsrTXH+VOU2QPi2zj3M/w06elCnov/KZYl/aSRerg viLquHK8sUymEq9KB7swIO+Kthk5G8fke/h/3xq1i4S0n6klajtU8HuOR5FdmcAU kfA05Czngzw= =gleH -----END PGP SIGNATURE-----