On 5/14/2019 7:29 PM, Hannes Tschofenig wrote:
Hi Paul,
My understanding from reading the draft text was that the "cost" was actually talking about
"energy cost" rather than "monetary cost".
The monetary cost may also be interesting.
It is difficult to judge the extra cost of a RNG in an MCU because
(a) you rarely find an MCU with and without MCU (keeping all other features the
same),
"with and without RNG"?
(b) even if you find one there are other factors that impact the cost (such as
popularity of a particular MCU),
(c) RNG features are often provided with other features (such as SHA256 and AES
in hardware), and
Um... you usually need one or the other of these to do a good
implementation of a DRBG and hardware versions tend to be less "costly"
energy wise than software ones.
(d) cost and price of an MCU are different aspects.
That have no bearing on the protocol design past a certain set of
minimums. I'm beginning to think its time for "minimum requirements
for internet hosts - 2020 edition" RFCs. We seem to be back in the same
set of arguments that ANYTHING should be able to be an internet device
albiet with even lower thresholds than we were a few years ago. ACE is
pushing those boundaries, but we seem to be chasing "cost -> 0"
Ciao
Hannes
All good points, but ignoring the fact that needs drive the protocols
which drive the MCU development. NOT MCUs limit the protocols which
limit the needs.
In other words, if the community (through protocol definitions) doesn't
require the RNG, then the MCU developers won't include it.
With respect to RNG energy costs - the argument that they are too
expensive energy wise is pretty bogus. RNGs generally have two parts -
a TRNG or entropy source, and a DRBG seeded from the entropy source.
The energy costs for the DRBG are microscopic. The energy costs for a
TRNG are related more to the time needed to initially fill the entropy
pool (e.g. getting the noisy diodes making noise, getting the ring
oscillators ringing etc) than to keeping it running to get a few
thousand bits. Doing this say once a year to seed the DRBG isn't going
to kill the lifetime of a battery device.
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