The passwords are stored in a database table, not a file, so that exact scenario won't work. But one could easily imagine some SQL injection attack or something like that making the passwords visible - which is a big reason I store them as MD5 hash values rather than plaintext. It certainly wouldn't be much work to add a salt, so no reason not to.
On Wed, May 20, 2009 at 3:07 PM, Jonathan Yu <jonathan.i...@gmail.com>wrote: > Bill: > > Perhaps there is a vulnerability in something else, like a PHP script > you use to show source code, that allows attackers to get the file. > You want to make sure the file is useless to people, even if they have > it, which I think is the worst-case scenario. > > They might not be able to download all files this way, as the program > might be restricted to showing ASCII files; so they will be able to > view your password file but not, say, the binary files stored on your > server in the passworded area that they want to get to. > > Never hurts to fix those things, really. It doesn't negatively impact > performance in a noticeable way, and the security benefits > dramatically outweigh the costs. > > Cheers, > > Jonathan > > On Wed, May 20, 2009 at 6:05 PM, Bill Ward <b...@wards.net> wrote: > > > > > > On Wed, May 20, 2009 at 2:55 PM, Jonathan Yu <jonathan.i...@gmail.com> > > wrote: > >> > >> Bill: > >> > >> To clarify why a salt is necessary, consider the classic time-space > >> tradeoff. Let's say I know that your password is exactly 8 characters > >> long and I know all of the possible characters it could be. So let's > >> say it's alphanumeric (a-z, A-Z, 0-9, hyphen, period, underscore) - > >> that's 26+26+10+3 = 65 possible combinations per character. > >> > >> Then you'd only have to generate a hash 65^8 = 318644812890625 times, > >> which for faster computers these days shouldn't take too long. Still, > >> it takes a lot of time, so you can store it all in a database (ie, > >> Rainbow Table). So if you map a bunch of arbitrary plaintexts and > >> calculate their hash, you can look up the hash and figure out what > >> text was used to generate that hash. Thus, you've either figured out > >> the password or an MD5 collision thereof; in either case, you'll be > >> able to log in. > >> > >> There are web sites that specialize in that sort of thing. So having a > >> 2-byte salt can really help stop those attacks, or at least make the > >> amount of space needed infeasible (since every different 2 character > >> salt will require you to generate an entirely different rainbow > >> table). > >> > >> For most uses it's probably unnecessary, however, if you can harden > >> security with just a few extra lines of code, why not? > > > > Yeah, but how would you get the MD5 hash without already having access to > > the database behind the web site, in which case the farm has already been > > given away? Still, it's not hard to add. > > > -- Check out my LEGO blog at http://www.brickpile.com/ View my photos at http://flickr.com/photos/billward/ Follow me at http://twitter.com/williamward
