netdev - Re: [PATCH 3/5] xfrm: Traffic Flow Confidentiality for IPv4 ESP

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Date:	Mon, 06 Dec 2010 16:10:25 +0100
From:	Martin Willi <martin@...ongswan.org>
To:	Herbert Xu <herbert@...dor.apana.org.au>
Cc:	linux-crypto@...r.kernel.org, netdev@...r.kernel.org
Subject: Re: [PATCH 3/5] xfrm: Traffic Flow Confidentiality for IPv4 ESP

Hi Herbert,

> I know why you want to do this, what I'm asking is do you have any
> research behind this with regards to security 
> 
> Has this scheme been discussed on a public forum somewhere?

No, sorry, I haven't found much valuable discussion about TFC padding.
Nothing at all how to overcome the ESPv2 padding limit.

> using an insecure RNG to generate a value that is then used as the
> basis for concealment

Using get_random_bytes() adds another ~10% processing overhead due to
the underlying sha_transform. But this is probably negligible, we add
much more with the additional padding to encrypt/MAC.

I'll re-spin the patchset with get_random_bytes(). Even if the ESPv2
padding fallback makes TFC in this case less efficient, it shouldn't
harm. Or do you see this differently?

Regards
Martin

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