[147885] in cryptography@c2.net mail archive
Re: [Cryptography] Randomness from network hardware?
daemon@ATHENA.MIT.EDU (David Mercer)
Tue Oct 29 18:45:40 2013
X-Original-To: cryptography@metzdowd.com
In-Reply-To: <B3AABCE3-5541-4AE6-9A2B-E31C1FE600DD@lrw.com>
Date: Wed, 30 Oct 2013 02:32:13 +0800
From: David Mercer <radix42@gmail.com>
To: Cryptography Mailing List <cryptography@metzdowd.com>
Errors-To: cryptography-bounces+crypto.discuss=bloom-picayune.mit.edu@metzdowd.com
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On Tue, Oct 29, 2013 at 4:50 AM, Jerry Leichter <leichter@lrw.com> wrote:
> Ethernet is supposed to back off randomly after a collision. There's no
> need for a strong notion of randomness, but the algorithm does have to
> introduce enough variation between stations that two of them will never end
> up following the same sequence of backoffs at the same time, or the
> algorithm won't work.
>
> Is there any way to get access to whatever source of randomness drives
> this decision? Old interfaces - I'm talking the original "yellow cable
> 10Mb/sec" stuff - used to have a test mode that would simulate a collision.
> I think you could even force one.
>
> I haven't looked at Ethernet hardware in many years/generations of the
> standards. Do current interfaces, perhaps in some test mode (which a
> special driver could get at during boot), provide access to anything that
> could be used as (part of) a random seed?
> -- Jerry
>
This wouldn't really be of practical use in current ethernet networks
because you don't actually get collisions unless you are using a hub. It's
hard to even find a hub to buy, as they don't work for connections over 100
Mbps, and they practically give away low end switches in cereal boxes these
days they are so cheap. And included on every DSL and cable modem. So its
all point to point ethernet traffic on anything newly deployed in most of
the last decade.
-David Mercer
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<div dir=3D"ltr">On Tue, Oct 29, 2013 at 4:50 AM, Jerry Leichter <span dir=
=3D"ltr"><<a href=3D"mailto:leichter@lrw.com" target=3D"_blank">leichter=
@lrw.com</a>></span> wrote:<br><div class=3D"gmail_extra"><div class=3D"=
gmail_quote">
<blockquote class=3D"gmail_quote" style=3D"margin:0 0 0 .8ex;border-left:1p=
x #ccc solid;padding-left:1ex">Ethernet is supposed to back off randomly af=
ter a collision. =C2=A0There's no need for a strong notion of randomnes=
s, but the algorithm does have to introduce enough variation between statio=
ns that two of them will never end up following the same sequence of backof=
fs at the same time, or the algorithm won't work.<br>
<br>
Is there any way to get access to whatever source of randomness drives this=
decision? =C2=A0Old interfaces - I'm talking the original "yellow=
cable 10Mb/sec" stuff - used to have a test mode that would simulate =
a collision. =C2=A0I think you could even force one.<br>
<br>
I haven't looked at Ethernet hardware in many years/generations of the =
standards. =C2=A0Do current interfaces, perhaps in some test mode (which a =
special driver could get at during boot), provide access to anything that c=
ould be used as (part of) a random seed?<br>
=C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=
=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =
=C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 =C2=A0 -- Jerry<br></blockquote><=
div><br></div><div>This wouldn't really be of practical use in current =
ethernet networks because you don't actually get collisions unless you =
are using a hub. It's hard to even find a hub to buy, as they don't=
work for connections over 100 Mbps, and they practically give away low end=
switches in cereal boxes these days they are so cheap. And included on eve=
ry DSL and cable modem. So its all point to point ethernet traffic on anyth=
ing newly deployed in most of the last decade.</div>
<div><br></div><div>-David Mercer</div><div>=C2=A0</div></div></div></div>
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