Reality check Others have pointed this out but I don't think it's making it through. LHash doesn't need a cryptographic hash and it doesn't have security implications. It certainly doesn't need a keyed hash.
LHash does need to be something that's good at distinguishing short text strings, that's not necessarilly the same thing as a good cryptographic hash, and possibly it's exactly the opposite thing due to the limitted incoming symbol space (ascii text). About the only thing LHash needs is high performance in it's use area. I'd suspect that switching MD5 to SHA-1 in the existing algorithm would get you that simply because SHA-1 is asm optimized on most platforms now and MD5 typically isn't. I'd suggest that anyone wishing to change this should at least have to demonstrate improved performance in the OpenSSL use case before it's accepted. Peter From: "Short, Todd" <tsh...@akamai.com> To: "openssl-dev@openssl.org" <openssl-dev@openssl.org> Date: 11/01/2017 08:42 Subject: Re: [openssl-dev] use SIPhash for OPENSSL_LH_strhash? Sent by: "openssl-dev" <openssl-dev-boun...@openssl.org> 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 // tsh...@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 <levi...@openssl.org> wrote: Benjamin Kaduk <bka...@akamai.com> skrev: (10 januari 2017 20:19:21 CET) On 01/10/2017 12:31 PM, Richard Levitte wrote: Benjamin Kaduk <bka...@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 -- Sent from my Android device with K-9 Mail. Please excuse my brevity. -- openssl-dev mailing list To unsubscribe: https://mta.openssl.org/mailman/listinfo/openssl-dev -- openssl-dev mailing list To unsubscribe: https://mta.openssl.org/mailman/listinfo/openssl-dev
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