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North American Network Operators Group Date Prev | Date Next | Date Index | Thread Index | Author Index | Historical Re: TCP SYN attacks - a simple solution
> The idea has been floated before, and I believe it to be the right > solution to this problem. However, I have some suggested improvements: > > 1. The use of a "per boot" secret number allows an attacker to > poll your machine to deduce the secret, and then attack you with > that knowledge. > > A solution to this problem is to use a rapidly changing secret, the > pattern of which cannot be easily deduced, and a sliding window of > acceptance. (If the hash doesn't match the current scheme, but matches > the scheme we were using in the past N seconds, then accept the packet) > > The change interval needs to be short enough that, by the time an > attacker has been able to compute the next number, the window for > accepting that has closed. I figure that if you steal 4 to 12 bytes for mss storage, 2^20 is still enough possibilities that you can just rotate your secret every minutes and test against the old one for 30 seconds... > -matthew kaufman > [email protected] Yes. > ps. I've been meaning to write this entire scheme, with the enhancements > I propose here, as a draft specification, but I keep getting interrupted > by flooded phone rooms and the like this weekend. *sigh* Hopefully there will be a working implementation of this by week's end. Jeff Weisberg has code which runs on sun3s and (soon, I hope) on other Suns under SunOS. This has always seemed to me to be the best way to do things, though an OS patch to go to hashed-entry into arrays of PCBs is a definite win to back-implement into SunOS (for example) in general. Avi - - - - - - - - - - - - - - - - -
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