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From:   Emil Lenngren <emil.lenngren@gmail.com>
Date:   Mon, 25 Mar 2019 13:23:44 +0100
Message-ID: <CAO1O6sfDYV9q5z2b64SS1MDSuXUYS6fvxQWc00NsX_1qLxEorQ@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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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 Rand
> 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