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Re: [TLS] record layer limits of TLS1.3

Yoav Nir <ynir.ietf@gmail.com> Wed, 23 November 2016 08:06 UTC

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From: Yoav Nir <ynir.ietf@gmail.com>
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Date: Wed, 23 Nov 2016 10:05:57 +0200
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To: Nikos Mavrogiannopoulos <nmav@redhat.com>
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Subject: Re: [TLS] record layer limits of TLS1.3
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Hi, Nikos

On 23 Nov 2016, at 9:06, Nikos Mavrogiannopoulos <nmav@redhat.com> wrote:

> Hi,
>  Up to the current draft of TLS1.3 the record layer is restricted to
> sending 2^14 or less. Is the 2^14 number something we want to preserve?
> 16kb used to be a lot, but today if one wants to do fast data transfers
> most likely he would prefer to use larger blocks. Given that the length
> field allows for sizes up to 2^16, shouldn't the draft allow for 2^16-
> 1024 as maximum?

I am not opposed to this, but looking at real browsers and servers, we see that they tend to set the size of records to fit IP packets. The gains from increasing the size of records from the ~1460 bytes that fit in a packet to nearly 64KB are not all that great, and the gains from increasing records from 16 KB to 64KB are almost negligible. At that size the block encryption dominates the CPU time.

Yoav

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