From: Stefan Seyfried <stefan.seyfried@googlemail.com>
To: Pavel Machek <pavel@ucw.cz>,
kernel list <linux-kernel@vger.kernel.org>,
security@kernel.org, linux-bluetooth@vger.kernel.org,
johan.hedberg@gmail.com, marcel@holtmann.org
Subject: Re: (Small) bias in generation of random passkeys for pairing
Date: Thu, 20 Jun 2019 14:00:38 +0200 [thread overview]
Message-ID: <66098773-4d88-ebdb-02d5-8af0cc4ea99c@message-id.googlemail.com> (raw)
In-Reply-To: <20190619162456.GA9096@amd>
Hi Pavel,
Am 19.06.19 um 18:24 schrieb Pavel Machek:
> Hi!
>
> There's a (small) bias in passkey generation in bluetooth:
>
> get_random_bytes(&passkey, sizeof(passkey));
> passkey %= 1000000;
> put_unaligned_le32(passkey, smp->tk);
>
> (there are at least two places doing this).
>
> All passkeys are not of same probability, passkey "000000" is more
> probable than "999999", but difference is small.
It is slightly different IMHO.
Unsigned 32bits passkey assumed (and all users I found were u32),
the passkeys "000000" to "967295" are slightly more probable than
"967296" to "999999".
If my math is right (which I doubt), the difference in probability
for both entities is 4294:4293.
> Do we care?
I, personally, don't (yet).
But then, I'm not a real security expert.
Have fun,
--
Stefan Seyfried
"For a successful technology, reality must take precedence over
public relations, for nature cannot be fooled." -- Richard Feynman
prev parent reply other threads:[~2019-06-20 12:00 UTC|newest]
Thread overview: 2+ messages / expand[flat|nested] mbox.gz Atom feed top
2019-06-19 16:24 (Small) bias in generation of random passkeys for pairing Pavel Machek
2019-06-20 12:00 ` Stefan Seyfried [this message]
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