Re: [TLS] Data volume limits

Aaron Zauner <> Fri, 01 January 2016 16:01 UTC

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Date: Fri, 1 Jan 2016 17:01:38 +0100
From: Aaron Zauner <>
To: Samuel Neves <>
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Subject: Re: [TLS] Data volume limits
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Hi Samuel,

* Samuel Neves <> [01/01/2016 12:19:36] wrote:
> OCB is, if anything, worse than GCM when it comes to data volume limits. It has the same confidentiality bounds as GCM
> (slightly worse, in fact), but once you hit a collision you also lose authenticity and enable simple forgeries [1].

If I understand correctly the same is true for GCM?

I did not say that OCB provides beyond-birthday bound security. I'm
well aware that the mode does not really affect this issue in that
particular case.

> The real issue here is the block size of AES, not the security bounds of particular modes. Those are by and large all
> limited by the birthday bound. You could go with more exotic beyond-birthday modes, but there don't seem to be any being
> proposed for TLS. The simple solution to the birthday blues is, of course, to use a larger block.

Sure. Agreed.

Thanks for the feedback,