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Re: [TLS] Record header size?

Viktor Dukhovni <ietf-dane@dukhovni.org> Wed, 18 November 2015 15:24 UTC

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Date: Wed, 18 Nov 2015 15:24:22 +0000
From: Viktor Dukhovni <ietf-dane@dukhovni.org>
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Subject: Re: [TLS] Record header size?
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On Wed, Nov 18, 2015 at 11:07:59AM +0200, Yoav Nir wrote:

> Stateful firewalls tend to pass only what they understand. They use some measures to avoid tunneling and passing things that are not HTTPS over TCP port 443.
> 

If the record layer header for application-data (not the initial
handshak), is simply expanded by 3 bytes to 8 (zero padded), and
the padding is included in the record length, then to legacy parsers
it looks like a 5 byte header with payload that's 3 bytes longer.
While implementations aware of the change will treat this as a new
format in which the recorder header is 8 bytes and always overstates
the payload length by 3.

The real payload can then be properly aligned.

-- 
	Viktor.

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