Re: [TLS] Reducing record expansion overhead allowance

Fabrice <fabrice.gautier@gmail.com> Sun, 20 July 2014 04:31 UTC

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From: Fabrice <fabrice.gautier@gmail.com>
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Date: Sat, 19 Jul 2014 21:31:53 -0700
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To: Eric Rescorla <ekr@rtfm.com>
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Subject: Re: [TLS] Reducing record expansion overhead allowance
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What are the benefits of reducing the allowed overhead?

-- Fabrice


> On Jul 19, 2014, at 11:56, Eric Rescorla <ekr@rtfm.com> wrote:
> 
> https://github.com/tlswg/tls13-spec/issues/55
> 
> In TLS 1.2, we had the following maximum values:
> 
> TLSPlaintext: 2^{14}
> TLSCompressed: 2^{14} + 1024
> TLSCiphertext: 2^{14} + 2048
> 
> These overhead values allow for expansion in these transforms
> due to potential bad compression overhead or padding, etc.
> 
> Wan-Teh Chang points out that we no longer have compression
> so there's no need to allow for 1024 bytes of expansion there.
> 
> Minimally we should reduce the TLSCiphertext overhead to
> 2^{14} + 1024. Do people believe that we will have AEAD
> ciphers with 1024 bytes of expansion or should we reduce
> it further? I'm inclined to not re-judge that and just leave it
> at 2^{14} + 1024.
> 
> Thoughts?
> -Ekr
> 
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