Hi Hannes,

Agree. The draft is already referencing RFC 7925, so it could additionally 
reference Section 12 (https://tools.ietf.org/html/rfc7925#section-12) which 
explains that randomness is also needed for all DTLS handshakes. What I mention 
about “being able to trust the randomness level” is then maybe a more 
psychological requirement rather than technical. A powerful server with RTC 
just sounds more capable to do private key generation than an IoT device, which 
is why server-side keygen may be preferred ;)

Esko

From: Hannes Tschofenig <hannes.tschofe...@arm.com>
Sent: Tuesday, May 14, 2019 18:46
To: Esko Dijk <esko.d...@iotconsultancy.nl>; Panos Kampanakis (pkampana) 
<pkamp...@cisco.com>; ace@ietf.org
Subject: RE: [Ace] EST over CoAP: Randomness

Hi Esko,

good to hear from you.


  *   Another reason for server-side keygen can be that an IT 
department/manager wants it that way. There could be a policy that the keypairs 
for all domain certificates must be created by the systems under direct control 
of the IT department. (E.g. to comply with other policies or to be able to 
trust the randomness level. Or just because that was the way it always has been 
when PCs were provisioned with certificates.)  This could be listed as an 
additional reason.

For readers interested in making informed decisions I believe it is worthwhile 
to point out that they need random number generation capabilities on IoT 
devices – not just for the private key generation in context of the EST 
exchange. I fear that some people, including IT managers, just glance over the 
details and focus on isolated aspects. I am sure you agree with me that this 
would be a too simplistic view.

Ciao
Hannes

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