Re: [Ace] [Secdispatch] FW: [secdir] EDHOC and Transports

"Valery Smyslov" <smyslov.ietf@gmail.com> Mon, 18 February 2019 07:07 UTC

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From: "Valery Smyslov" <smyslov.ietf@gmail.com>
To: "'Michael Richardson'" <mcr+ietf@sandelman.ca>, "'Richard Barnes'" <rlb@ipv.sx>
Cc: '=?UTF-8?Q?G=C3=B6ran_Selander?=' <goran.selander@ericsson.com>, <secdispatch@ietf.org>, <ace@ietf.org>
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Date: Mon, 18 Feb 2019 10:07:05 +0300
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Subject: Re: [Ace] [Secdispatch] FW: [secdir] EDHOC and Transports
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Hi,

> Richard Barnes <rlb@ipv.sx> wrote:
>     > Finally, to be totally honest, I find the EDHOC spec pretty inscrutable. A
>     > little more prose to explain what's going on would go a long way toward
>     > helping this discussion be productive.
> 
> Sure.
> Find a WG to adopt it, and we can make the text beautiful.
> The packets are all there, and the references pretty much explain all the crypto.
> This stuff is not any newer than IKEv2.

I have only a quick look over the draft, but one thing strikes me - the protocol 
is claimed not to bound to a particular transport (so I assume that implementing
it on top of pure UDP is fine), and it has an odd number of messages.
That's OK from cryptographic point of view, but it's a headache for 
implementations if the transport protocol is unreliable, since in this case retransmissions 
must be sent by both parties. We learned this lesson from IKEv1 (Aggressive and Quick modes) 
and in IKEv2 the number of messages in any exchange is always even, 
that simplifies implementations and makes protocol more reliable.
Of course if only reliable transports are considered, then this doesn't matter.

Regards,
Valery Smyslov.