netdev - RE: [PATCH v5 1/4] siphash: add cryptographically secure PRF

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Date:   Fri, 16 Dec 2016 17:06:57 +0000
From:   David Laight <David.Laight@...LAB.COM>
To:     'George Spelvin' <linux@...encehorizons.net>,
        "ak@...ux.intel.com" <ak@...ux.intel.com>,
        "davem@...emloft.net" <davem@...emloft.net>,
        "ebiggers3@...il.com" <ebiggers3@...il.com>,
        "hannes@...essinduktion.org" <hannes@...essinduktion.org>,
        "Jason@...c4.com" <Jason@...c4.com>,
        "jeanphilippe.aumasson@...il.com" <jeanphilippe.aumasson@...il.com>,
        "kernel-hardening@...ts.openwall.com" 
        <kernel-hardening@...ts.openwall.com>,
        "linux-crypto@...r.kernel.org" <linux-crypto@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "luto@...capital.net" <luto@...capital.net>,
        "netdev@...r.kernel.org" <netdev@...r.kernel.org>,
        "tom@...bertland.com" <tom@...bertland.com>,
        "torvalds@...ux-foundation.org" <torvalds@...ux-foundation.org>,
        "tytso@....edu" <tytso@....edu>,
        "vegard.nossum@...il.com" <vegard.nossum@...il.com>
CC:     "djb@...yp.to" <djb@...yp.to>
Subject: RE: [PATCH v5 1/4] siphash: add cryptographically secure PRF

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