If you do not use BitFolk's Entropy service and have no interest in
doing so then this email will be of little interest to you can be
If you haven't heard about the Entropy service before, please see:
If you *do* use the Entropy service though, I'm interested to know
what software you have that actually uses /dev/random (and not
Some background to this question:
To provide the Entropy service we use hardware entropy generators,
currently exclusively a pair of EntropyKeys manufactured by a UK
company called Simtec Electronics Ltd.
Despite the fact that these were extremely popular little devices
(compared to other fairly niche little gadgets), Simtec always had a
supply problem and then Simtec imploded as a company, so as far as I
know these are now impossible to obtain, the IP is lost forever etc.
Although I have one spare EntropyKey ready to put in service should
one of the two in service ever die (I've not experienced that yet),
that left me slightly worried as to what I'd do if I needed to get
Then I saw the OneRNG kickstarter, and decided to pledge. So now I
have 5 of (the internal USB version of) these:
I've not yet gone any further than verifying that they keep the
entropy pool full on the machine they're plugged into, but that's
good enough for now. Could be a decade before one of my existing
I have since heard that this device proved far more popular than its
manufacturer expected (sense a theme?) and they're now extremely
difficult to get hold of because they need to get a new batch made
in China. I've had multiple people contacting me on the basis of a
tweet I did about getting these, asking me to sell them mine (which
I would, but they didn't want internal USB).
The point I'm trying to make here is that the world of hardware
random number generators is not one with reliable supply lines,
unless you want to spend a fortune on some black box.
So when I came across:
I was sad that the nerdery that is the Entropy service may be
misguided, but also happy with the possibility that I might never
have to source a hardware RNG again.
Let's just take the argument posited by the article, that all
(Linux) software should just learn to love /dev/urandom¹, as true.
If you don't agree with this claim, you are disagreeing with some
pretty big names in crypto. The Hacker News commentary on the
article may also prove of interest:
At the very least, I feel the Entropy article on the BitFolk Wiki
needs an update in light of this. To justify the service's
existence, if nothing else.
Going further, the question becomes, well, what software is there in
existence that forces use of /dev/random with no configuration that
would allow otherwise? Because even if we agree that all software
*should* be using urandom, if some popular software *refuses* to
without recompile, then we're still going to have to provide an
Entropy service, because doing so is easier than running
So Entropy service users, what have you got that uses /dev/random?
¹ A more correct summary of it is probably, "urandom is fine all the
time except for on initial boot when a small amount of entropy
from outside the CSPRNG is desirable."
On shutdown all fairly modern Linuxes save the current entropy
pool to the filesystem and load it up from there on boot, so it's
only essential on first boot.
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