netdev - Re: arp

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Message-ID: <20150322235308.GA9373@gondor.apana.org.au>
Date:	Mon, 23 Mar 2015 10:53:08 +1100
From:	Herbert Xu <herbert@...dor.apana.org.au>
To:	David Miller <davem@...emloft.net>
Cc:	eric.dumazet@...il.com, netdev@...r.kernel.org,
	roland@...estorage.com
Subject: Re: arp_hash

On Sun, Mar 22, 2015 at 07:50:03PM -0400, David Miller wrote:
>
> BTW I asked for feedback when I posted the patches which created this
> situation, and the multiply with the random input was believed to have
> sufficient entropy and not create a situation any worse,
> asymptotically, than what we had beforehand.

I know.  I just didn't know at the time or I would have objected :)

> Perhaps the ipv6 case can be improved, by using a u32 random input
> for each u32 of the address being hashed.

See my follow-up email.  The multiplication is useless against
an adversary, even if you multiply it against a secret odd value
because there is a bit-to-bit correspondence between the key and
the final hash value.

Cheers,
-- 
Email: Herbert Xu <herbert@...dor.apana.org.au>
Home Page: http://gondor.apana.org.au/~herbert/
PGP Key: http://gondor.apana.org.au/~herbert/pubkey.txt
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