Re: [TLS] Are the AEAD cipher suites a security trade-off win with TLS1.2?

Colm MacCárthaigh <colm@allcosts.net> Wed, 16 March 2016 18:43 UTC

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Date: Wed, 16 Mar 2016 14:42:57 -0400
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From: =?UTF-8?Q?Colm_MacC=C3=A1rthaigh?= <colm@allcosts.net>
To: Adam Langley <agl@imperialviolet.org>
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Subject: Re: [TLS] Are the AEAD cipher suites a security trade-off win with TLS1.2?
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On Wed, Mar 16, 2016 at 2:30 PM, Adam Langley <agl@imperialviolet.org>;
wrote:

> On Wed, Mar 16, 2016 at 6:14 PM, Paterson, Kenny
> <Kenny.Paterson@rhul.ac.uk>; wrote:
> >>provokes me to bring it up. Here's the crux of it; is it really a
> >>security win to recommend the AEAD cipher suites for TLS 1.2 users?
>
> I'm skeptical about the benefit of padding to 16 bytes. While it does
> increase the size classes in your Wikipedia example, Wikipedia pages
> trigger subresource loads, which also have a size and page-to-page
> navigation leaks more information. My takeaway from reading
> traffic-analysis papers over the years is that countermeasures are
> surprisingly difficult.
>

16-bytes is small, I wish it were much bigger, but it may elevate things to
where you even need to form a sub resource attack and increases the size of
the graph/fingerprint that you need to maintain to form the sub-resource
attack. I doubt it would thwart a large actor for very long, but it would
help against smaller ones and I'm guessing that it might block some
specific attacks like the autocompletion one mentioned in the paper.


-- 
Colm