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From:   Emil Lenngren <emil.lenngren@gmail.com>
Date:   Fri, 18 Jan 2019 08:51:10 -0500
Message-ID: <CAO1O6sfFqcQvn2Sy_HOLAzuc9o-Wu0g_9oLH-OFOkCxfuA=Jtg@mail.gmail.com>
Subject: Re: Bluetooth ECDH selftest failed (endianness issue?)
To:     Marcel Holtmann <marcel@holtmann.org>
Cc:     Andrey Batyiev <batyiev@gmail.com>,
        Johan Hedberg <johan.hedberg@gmail.com>,
        Bluez mailing list <linux-bluetooth@vger.kernel.org>
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Hi,

Den fre 18 jan. 2019 kl 04:44 skrev Marcel Holtmann <marcel@holtmann.org>:
>
> Hi Andrey,
>
> >> On Sat, Dec 29, 2018 at 9:35 AM Marcel Holtmann <marcel@holtmann.org> =
wrote:
> >> I think that our ECDH code was endian safe, but then it got changed at=
 some point to use standard crypto and maybe something went wrong there. Ca=
n just provide the btmon -w trace.log for the SMP pairing so that I can hav=
e a look at the binary trace.
> >
> > I found out that if I change "swap_digits" method in
> > "net/bluetooth/ecdh_helper.c" to
> >
> > static inline void swap_digits(u64 *in, u64 *out, unsigned int ndigits)
> > {
> > int i;
> >
> > for (i =3D 0; i < ndigits; i++)
> >        out[i] =3D in[ndigits - 1 - i];
> > }
> >
> > then BLE pairing on big-endian become operational. I'm not sure what
> > proper fix should be: is it a problem with crypto API usage or a
> > problem with crypto itself?
>
> if the kernel ECC and ECDH crypto already swaps for us, then we don=E2=80=
=99t need to do it again. So all the swap_digits most likely can be removed=
 from net/bluetooth/.
>
> Regards
>
> Marcel
>

The Bluetooth standard is a bit strange. It assumes the AES standard
is big endian (although it is really just defined on a byte level),
but since Bluetooth is little-endian everywhere, all AES 128-bit
values must be reversed when a standard AES library is used. In
particular, SMP reverses the AES values. So the swap_digits should be
kept.

/Emil