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From:   Emil Lenngren <emil.lenngren@gmail.com>
Date:   Mon, 25 Mar 2019 14:01:00 +0100
Message-ID: <CAO1O6sdC8fuFjAh5J-O-qjcaaaft8WfepKLFgXQZpAf-TKkXQQ@mail.gmail.com>
Subject: Re: Information about HCI LE Rand command
To:     Alexandre Augusto <alexandre.a.giron@gmail.com>
Cc:     Bluez mailing list <linux-bluetooth@vger.kernel.org>
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Den m=C3=A5n 25 mars 2019 kl 13:40 skrev Alexandre Augusto
<alexandre.a.giron@gmail.com>:
>
> Thanks Emil.
>
> The reason I asked is that I am researching ways to provide that
> "minimum entropy required", and I was not able to find details about
> the number generation.
>
> Best regards,
> Alexandre Giron
>
> Em seg, 25 de mar de 2019 =C3=A0s 09:23, Emil Lenngren
> <emil.lenngren@gmail.com> escreveu:
> >
> > Hi Alexandre,
> >
> > Den m=C3=A5n 25 mars 2019 kl 13:03 skrev Alexandre Augusto
> > <alexandre.a.giron@gmail.com>:
> > >
> > > Hello,
> > >
> > > I would like to know, if possible, information about the bluez LE Ran=
d
> > > command (ocf 0x0018) at HCI code. How does it generate the number? Is
> > > it vendor-specific (or secret)?
> >
> > According to the Bluetooth core specification, it shall be a "A pseudo
> > random number generator compliant with [FIPS PUB 140-2]
> > (http://csrc.nist.gov/publications/fips/fips140-2/fips1402annexc.pdf)"
> > which shall be seeded "with at least the minimum entropy required by
> > the pseudo random number generator". What algorithm each Bluetooth
> > controller actually uses is therefore vendor specific. I guess most
> > controllers will use some SHA-based or AES-based algorithm. Note that
> > it is not the host (BlueZ) that generates the number; it just asks the
> > controller to generate it for the host.
> >
> > /Emil

I'm a aware of two different vendors. One vendor has a hardware-based
random number generator based on thermal inner noise that is used to
feed the CSPRNG
(https://www.nordicsemi.com/DocLib/Content/Product_Spec/nRF52810/latest/rng=
).
The other vendor uses the radio to gather enough random bits from the
air.

/Emil