Re: [Ace] EST over CoAP: Randomness

Paul Duffy <> Wed, 15 May 2019 14:30 UTC

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To: Hannes Tschofenig <>, "" <>
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From: Paul Duffy <>
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Date: Wed, 15 May 2019 10:30:18 -0400
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Subject: Re: [Ace] EST over CoAP: Randomness
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The point I'm making Hannes is that,  though not so long ago the "cost" 
for RNG was prohibitive for many constrained end-devices ... this is 
more often no longer the case and improving every month (despite 
whatever other security functions are packaged within the module).

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),
> (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
> (d) cost and price of an MCU are different aspects.
> Ciao
> Hannes
> -----Original Message-----
> From: Paul Duffy <>
> Sent: Dienstag, 14. Mai 2019 15:08
> To: Hannes Tschofenig <>om>;
> Subject: Re: [Ace] EST over CoAP: Randomness
> On 5/9/2019 10:42 AM, Hannes Tschofenig wrote:
>> I believe we should encourage developers to pick the correct hardware for the task rather than making them believe we have come up with solutions that allow them to get away without a hardware-based RNG.
>> I also do not believe the statement that random number key generation is costly. Can you give me some number?
> Strong agreement.  The added cost for hw based RNG is ever decreasing. Last time I checked it was on the order of 50 cents @ Q 10k?  It has likely fallen since.  Confirm with Atmel etc.
> Cheers
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