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Re: [TLS] Heartbeat and padding

Nico Williams <nico@cryptonector.com> Tue, 29 April 2014 01:43 UTC

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From: Nico Williams <nico@cryptonector.com>
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Subject: Re: [TLS] Heartbeat and padding
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On Mon, Apr 28, 2014 at 6:57 PM, Viktor Dukhovni
<viktor1dane@dukhovni.org> wrote:
> On Mon, Apr 28, 2014 at 04:10:09PM -0700, Bill Frantz wrote:
> However, a heartbeat over TCP does not require any payload or
> response.  It can be a record-layer message with a zero-length
> payload that elicits no response at all.  This gets no cryptographic
> protection, but that just makes it cheaper and safer.

Arguably even a TCP application with keepalives might want to keep
PMTUD going on idle connections (sending large keepalives from time to
time to keep the PMTUD info fresh) so that when they get busy they go
fast, but that might be significantly wasteful unless also coupled
with an exponential idle backoff.

But, sure, as to TCP I think we can remove the variable-length payload
heartbeat.

I'm somewhat concerned by having too many special case differences
between DTLS and TLS though.  We've already seen a mistake that meant
that DTLS Hellos cannot carry extensions.

Nico
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