From: George Spelvin > Sent: 15 December 2016 23:29 > > If a halved version of SipHash can bring significant performance boost > > (with 32b words instead of 64b words) with an acceptable security level > > (64-bit enough?) then we may design such a version. > > I was thinking if the key could be pushed to 80 bits, that would be nice, > but honestly 64 bits is fine. This is DoS protection, and while it's > possible to brute-force a 64 bit secret, there are more effective (DDoS) > attacks possible for the same cost. A 32bit hash would also remove all the issues about the alignment of IP addresses (etc) on 64bit systems. > (I'd suggest a name of "HalfSipHash" to convey the reduced security > effectively.) > > > Regarding output size, are 64 bits sufficient? > > As a replacement for jhash, 32 bits are sufficient. It's for > indexing an in-memory hash table on a 32-bit machine. It is also worth remembering that if the intent is to generate a hash table index (not a unique fingerprint) you will always get collisions on the final value. Randomness could still give overlong hash chains - which might still need rehashing with a different key. David -- To unsubscribe from this list: send the line "unsubscribe linux-crypto" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
