[openssl-dev] use SIPhash for OPENSSL_LH_strhash?

[Short, Todd]

I think I might have an init/update/final version of siphash24 lying around somewhere that would be compatible with OpenSSL’s EVP_PKEY mechanism (similar to Poly1305, in that it needs a key).
--
-Todd Short
// tshort at akamai.com<mailto:tshort at akamai.com>
// "One if by land, two if by sea, three if by the Internet."

On Jan 10, 2017, at 4:55 PM, Richard Levitte <levitte at openssl.org<mailto:levitte at openssl.org>> wrote:



Benjamin Kaduk <bkaduk at akamai.com<mailto:bkaduk at akamai.com>> skrev: (10 januari 2017 20:19:21 CET)
On 01/10/2017 12:31 PM, Richard Levitte wrote:

Benjamin Kaduk <bkaduk at akamai.com<mailto:bkaduk at akamai.com>> skrev: (10 januari 2017 18:48:32
CET)
On 01/09/2017 10:05 PM, Salz, Rich wrote:
Should we move to using SIPHash for the default string hashing
function in OpenSSL?  It’s now in the kernel
https://lkml.org/lkml/2017/1/9/619

Heck, yes!
-Ben
I fail to see what that would give us. OPENSSL_LH_strhash() is used
to get a reasonable index for LHASH entries. Also SIPhash gives at
least 64 bits results, do we really expect to see large enough hash
tables to warrant that?


We don't need to use the full output width of a good hash function.

My main point is, "why would we want to ignore the last 20 years of
advancement in hash function research?"  Section 7 of the siphash paper
(https://131002.net/siphash/siphash.pdf) explicitly talks about using
it
for hash tables, including using hash table indices H(m) mod l.

I agree with the advice when one can expect huge tables. The tables we handle are pretty small (I think, please correct me if I'm wrong) and would in all likelihood not benefit very much if at all from SIPhash's relative safety.

Of course, one can ask the question if someone uses LHASH as a general purpose hash table implementation rather than just for the stuff OpenSSL. Frankly, I would probably look at a dedicated hash table library first...

Cheers
Richard
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