msieve | C library implementing a suite of algorithms to factor

Q. I want to factor much bigger numbers. Can't Msieve solve problems larger than you say? Q. I'm trying to break my ex-girlfriend's RSA key with Msieve, and it's not working. What's wrong? A. The quadratic sieve really is not appropriate for factoring numbers over ~110 digits in size. On a fast modern CPU, a 110-digit QS factor- ization takes nearly 120 hours for Msieve, and the time increases steeply beyond that. If you have really big factorization needs, there are several packages that you can use to make up for the low-performance parts of Msieve's NFS code:. See later for a list of web resources that give an idea of the largest actual factorizations that Msieve has performed. Q. Can you make Msieve network aware? Can you make it a client-server thingy? Can I use the internet to factor numbers? A. The demo application for the Msieve library is just that, a demo. I don't know anything about network programming and I'm not qualified to build a client-server application that's safe in the face of internet threats. If you have these kinds of smarts, you can use Msieve in your own code and I'll help as much as I can. The demo is good enough for people with a few machines on a small private LAN, and this is ~100% of the user community right now. Q. Where's all the documentation on how your library actually works? A. There really isn't any. Msieve is a spare-time project, and I have so little spare time that if I tried to produce formal documents on the internals of the library then I'd never have time to actually work on those internals. The parts of the code that are relatively stable have extensive in-line documentation, but whatever I happen to be working on currently is pretty much comment-free. If you have specific questions about how a specific part of the code works, just ask... Q. How can I modify Msieve to work on a cluster? A. Distributed sieving is so easy that you don't need high-performance parallel programming techniques or message passing libraries to do it. If you're lucky enough to have a cluster then the batch scheduling system that comes with the cluster is more than enough to implement cluster-aware sieving. Of course if you have access to that much firepower you owe it to yourself to use an NFS package of some sort. Q. Can you modify Msieve to run on multi-core processors? A. As described above, the really intensive part of the QS and NFS algorithms is the sieving, and it's a waste of effort to multithread that. You won't save any time compared to just running two copies of Msieve. The final stage can benefit from multithreading, and the intensive parts of that are already multithread-aware. This can be improved, but multithreading more parts of the library is a low priority for me. Q. Why put Msieve into the public domain and not make it GPL? Wouldn't GPL-ed code protect your work and encourage contributions? A. Msieve is a learning exercise, not a collaborative effort per se. I don't expect other developers to help, though many have and it's appreciated. As for protection, there's only one way to generate income from this code: use it to win factoring contests. While the number field sieve can win factoring contests, you personally do not have the resources to do so. So there's no reason to put licensing restrictions on this code. Q. Your multiple precision library sucks. Why didn't you use GMP? A. I know it sucks. Using GMP would have left MSVC users in the cold, and even building GMP is a major exercise that requires essentially a complete and up-to-date unix environment. The nice thing about sieve- based factoring is that for big factorizations the actual multiple precision math takes about 1% of the total runtime, so it actually doesn't matter all that much which low-level multiple precision library is used. Actually, the parts of the code that use my own library are pretty old, and new development does require GMP. This became necessary after modifications to the NFS code started to require arithmetic on very large numbers, so GMP is now a requirement. One of my eventual goals is to phase out (most of) my own bignum library in favor of GMP.