Re: [TLS] I-D Action: draft-ietf-tls-tlsflags-00.txt

Ilari Liusvaara <ilariliusvaara@welho.com> Mon, 12 August 2019 22:39 UTC

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Date: Mon, 12 Aug 2019 21:25:19 +0300
From: Ilari Liusvaara <ilariliusvaara@welho.com>
To: tls@ietf.org
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Subject: Re: [TLS] I-D Action: draft-ietf-tls-tlsflags-00.txt
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On Mon, Aug 12, 2019 at 10:48:55AM -0700, internet-drafts@ietf.org wrote:
> 
> A New Internet-Draft is available from the on-line Internet-Drafts directories.
> This draft is a work item of the Transport Layer Security WG of the IETF.
> 
>         Title           : A Flags Extension for TLS 1.3
>         Author          : Yoav Nir
> 	Filename        : draft-ietf-tls-tlsflags-00.txt
> 	Pages           : 6
> 	Date            : 2019-08-12
> 
> 
> The IETF datatracker status page for this draft is:
> https://datatracker.ietf.org/doc/draft-ietf-tls-tlsflags/
> 
> There are also htmlized versions available at:
> https://tools.ietf.org/html/draft-ietf-tls-tlsflags-00
> https://datatracker.ietf.org/doc/html/draft-ietf-tls-tlsflags-00

Two things:


1) uint8 flags<0..31>;

That adds an extra byte that is not technically necressary (because
extensions have lengths anyway) and limits number of flags to 248
(which might be enough).

And I do not think the length of flags field can be 0 (if it would
be, one could just omit the extension).


2) I think the bit order within octets should be reversed

That is, pack flags so that 0 is LSB of first octet, 7 is MSB of
first octet, 8 is LSB of second octet and so on.

Then one can read status flags by index with code like:

fn read_flag(flags: &[u8], idx: usize) -> bool
{
        *flags.get(idx/8).unwrap_or(&0) >> idx%8 & 1 != 0
}

(That code will also happily handle out-of-array flags by reading
them as false.)



-Ilari