From eugen@leitl.org Fri Sep 13 03:54:59 2013
From: Eugen Leitl <eugen@leitl.org>
To: cypherpunks@lists.cpunks.org
Subject:
 Re: [cryptography] very little is missing for working BTNS in Openswan
Date: Fri, 13 Sep 2013 09:54:54 +0200
Message-ID: <20130913075454.GO10405@leitl.org>
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----- Forwarded message from Nico Williams <nico(a)cryptonector.com> -----

Date: Thu, 12 Sep 2013 14:04:08 -0500
From: Nico Williams <nico(a)cryptonector.com>
To: Eugen Leitl <eugen(a)leitl.org>
Cc: cryptography(a)randombit.net, Cryptography List <cryptography(a)metzdowd.=
com>
Subject: Re: [cryptography] very little is missing for working BTNS in Opensw=
an
User-Agent: Mutt/1.5.21 (2010-09-15)

On Mon, Sep 09, 2013 at 10:25:03AM +0200, Eugen Leitl wrote:
> Just got word from an Openswan developer:
>=20
> "
> To my knowledge, we never finished implementing the BTNS mode.
>=20
> It wouldn't be hard to do --- it's mostly just conditionally commenting out
> code.
> "
> There's obviously a large potential deployment base for
> BTNS for home users, just think of Openswan/OpenWRT.

Note: you don't just want BTNS, you also want RFC5660 -- "IPsec
channels".  You also want to define a channel binding for such channels
(this is trivial).

To summarize: IPsec protects discrete *packets*, not discrete packet
*flows*.  This means that -depending on configuration- you might be
using IPsec to talk to some peer at some address at one moment, and the
next you might be talking to a different peer at the same address, and
you'd never know the difference.  IPsec channels consist of ensuring
that the peer's ID never changes during the life of a given packet flow
(e.g., TCP connection).  BTNS pretty much requires IPsec configurations
of that make you vulnerable in this way.  I think it should be obvious
now that "IPsec channels" is a necessary part of any BTNS
implementation.

Nico
--=20

----- End forwarded message -----
--=20
Eugen* Leitl <a href=3D"http://leitl.org">leitl</a> http://leitl.org
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