Re: [TLS] custom lower limit of record_size_limit

Martin Thomson <mt@lowentropy.net> Mon, 21 January 2019 05:13 UTC

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From: Martin Thomson <mt@lowentropy.net>
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Date: Mon, 21 Jan 2019 16:13:47 +1100
Archived-At: <https://mailarchive.ietf.org/arch/msg/tls/s1uJp6NBrp39pFFap2S9pNdjaYk>
Subject: Re: [TLS] custom lower limit of record_size_limit
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On Sat, Jan 19, 2019, at 19:02, Daiki Ueno wrote:
> My interpretation is that, if the client sent "record_size_limit" but
> didn't receive the extension from the server, that would mean the
> extension was not negotiated and the server may not respect the limit.
> 
> Is this correct, or 64 is really mandatory to implement?

Unfortunately, if you want your peer to respect your limit, then you have to be willing to generate very small records.

BTW, 64 is entirely an arbitrary number.  It's at the point where the overheads get really noticeable, so performance is probably pretty bad well before you get to this point.  But we didn't get any indication that it was impossible to go that low.

If there had been feedback about it being too small, I'm fairly sure that a large number would have been fine.  Do you know why 64 is considered too hard to implement?