If you want DoS-resistant hash tables, I'm working on adding SipHash to the kernel.
This is a keyed pseudo-random function designed specifically for that application. I am starting with ext4 directory hashes, and then intended to expand to secure sequence numbers (since it's far faster than MD5). (I'm trying to figure out a good interface, since the crypto API is a bit heavy for something to heavily optimized.) But one comment caught my eye: > Even if security wasn't an issue, straight CRC32 has really poor > lower-order bit distribution, which makes it a terrible choice for > a hash table that simply uses the lower-order bits. Er... huh? That's the first time I've heard that claim, and while I'm not Philip Koopman or Guy Castagnoli, I thought I understood CRCs pretty well. CRCs generally mix bits pretty well. The sparse 16-bit CRCs chosen for implementation simplicity had some limitations, but the Castagnoli polynomial is quite dense. And their mathematical symmetry means that the low bits really shouldn't be any different from any other bits. But if it is an issue, it's just as easy work to shift down the correct number of high bits rather than using the low. Can you point me to a source for that statement? -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
