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Date: Wed, 14 Dec 2016 23:56:41 +0100
From: "Jason A. Donenfeld" <>
To: Tom Herbert <>
Cc: Netdev <>,, 
	LKML <>, 
	Linux Crypto Mailing List <>, 
	Jean-Philippe Aumasson <>, "Daniel J . Bernstein" <>, 
	Linus Torvalds <>, Eric Biggers <>, 
	David Laight <>
Subject: Re: [PATCH v3 1/3] siphash: add cryptographically secure hashtable function

Hey Tom,

On Wed, Dec 14, 2016 at 10:35 PM, Tom Herbert <> wrote:
> Those look good, although I would probably just do 1,2,3 words and
> then have a function that takes n words like jhash. Might want to call
> these dword to distinguish from 32 bit words in jhash.

So actually jhash_Nwords makes no sense, since it takes dwords
(32-bits) not words (16-bits). The siphash analog should be called

I think what I'll do is change what I already have to:

And then add some static inline helpers to assist with smaller u32s
like ipv4 addresses called:


While we're having something new, might as well call it the right thing.

> Also, what is the significance of "24" in the function and constant
> names? Can we just drop that and call this siphash?

SipHash is actually a family of PRFs, differentiated by the number of
SIPROUNDs after each 64-bit input is processed and the number of
SIPROUNDs at the very end of the function. The best trade-off of speed
and security for kernel usage is 2 rounds after each 64-bit input and
4 rounds at the end of the function. This doesn't fall to any known
cryptanalysis and it's very fast.

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