Re: [TLS] Reducing record expansion overhead allowance

On Sat, Jul 19, 2014 at 9:31 PM, Fabrice <fabrice.gautier@gmail.com> wrote:

> What are the benefits of reducing the allowed overhead?
>

It's good to have some fixed overhead to make implementation easier.

The benefit to reducing it to 1024 is mostly consistency of assumptions
about the AEAD ciphers.

-Ekr

> -- 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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