path: root/a5/c1e7df3dd88fb8f8d0c463c5fe1360e7ff573f

Received: from sog-mx-1.v43.ch3.sourceforge.com ([172.29.43.191]
	helo=mx.sourceforge.net)
	by sfs-ml-4.v29.ch3.sourceforge.com with esmtp (Exim 4.76)
	(envelope-from <eric@voskuil.org>) id 1YIRYJ-00058p-OI
	for bitcoin-development@lists.sourceforge.net;
	Tue, 03 Feb 2015 00:41:15 +0000
Received: from mail-pa0-f50.google.com ([209.85.220.50])
	by sog-mx-1.v43.ch3.sourceforge.com with esmtps (TLSv1:RC4-SHA:128)
	(Exim 4.76) id 1YIRYI-0005my-HJ
	for bitcoin-development@lists.sourceforge.net;
	Tue, 03 Feb 2015 00:41:15 +0000
Received: by mail-pa0-f50.google.com with SMTP id rd3so88897045pab.9
	for <bitcoin-development@lists.sourceforge.net>;
	Mon, 02 Feb 2015 16:41:08 -0800 (PST)
X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed;
	d=1e100.net; s=20130820;
	h=x-gm-message-state:message-id:date:from:user-agent:mime-version:to
	:cc:subject:references:in-reply-to:content-type;
	bh=DmZ9Nmv+r2Rwtnkbr94fXHbq8xFPUYyHcNDGq+5vaBk=;
	b=Q7celWAgJuOCqWPEBhOFjtVIJdoD7Vf3WPRd88+re+jgD81jMNHfOevJVSDN6N8RP4
	3Lo32wvNhB8b7wHU4ju5qDzzGfu0q9x5JjZB+1WeWDXCkOS2DHZdIPMerr6NL5YaEldu
	wls3C2MrvU5chPzdke99Li+RmPFlg96Prvc62l1VXqfDOZv6FwNLuzwuUW++o/MNnEHN
	jbxDzk4mx28g3UHsKjkQpKO0V8tR/hFE6pBOOCSsRfX3cwaSLCPeOpJ9DO9EoyQAfe5D
	+Dg3ZcHOg3XlydhIU+M9vWz9iCtVpjNBjZT90wpTWdfbKL7r60DNdQIcpTF7SuIp3o4K
	k3zw==
X-Gm-Message-State: ALoCoQmGywxjNuTmL4jb6N+HvZuAl8HDfbY0+wSgQKd0zZaSvca5vMHtRIqYUkiXNyCLiXJO+C7c
X-Received: by 10.66.141.42 with SMTP id rl10mr21489429pab.124.1422924068732; 
	Mon, 02 Feb 2015 16:41:08 -0800 (PST)
Received: from [10.0.1.3] (c-50-135-46-157.hsd1.wa.comcast.net.
	[50.135.46.157])
	by mx.google.com with ESMTPSA id q1sm249236pdq.17.2015.02.02.16.41.07
	(version=TLSv1.2 cipher=ECDHE-RSA-AES128-GCM-SHA256 bits=128/128);
	Mon, 02 Feb 2015 16:41:08 -0800 (PST)
Message-ID: <54D01930.10104@voskuil.org>
Date: Mon, 02 Feb 2015 16:41:20 -0800
From: Eric Voskuil <eric@voskuil.org>
User-Agent: Mozilla/5.0 (X11; Linux x86_64;
	rv:31.0) Gecko/20100101 Thunderbird/31.2.0
MIME-Version: 1.0
To: Mike Hearn <mike@plan99.net>
References: <27395C55-CF59-4E65-83CA-73F903272C5F@gmail.com>
	<54CE3816.6020505@bitwatch.co>
	<68C03646-02E7-43C6-9B73-E4697F3AA5FD@gmail.com>
	<05590A33-1802-4C15-91C0-8777ACD8440B@voskuil.org>
	<CANEZrP1QgtJ2urNTVqbscrXaJ=wefUO16GQ=THaSBnLq9QBmeQ@mail.gmail.com>
	<1F2B5D9D-BD1E-4EFB-AD48-4B3E376D9661@voskuil.org>
In-Reply-To: <1F2B5D9D-BD1E-4EFB-AD48-4B3E376D9661@voskuil.org>
Content-Type: multipart/signed; micalg=pgp-sha1;
	protocol="application/pgp-signature";
	boundary="uTb2NBheAWRWCFahxfJP01PjuEUMw6UwL"
X-Spam-Score: 0.0 (/)
X-Spam-Report: Spam Filtering performed by mx.sourceforge.net.
	See http://spamassassin.org/tag/ for more details.
X-Headers-End: 1YIRYI-0005my-HJ
Cc: Bitcoin Dev <bitcoin-development@lists.sourceforge.net>
Subject: Re: [Bitcoin-development] Proposal to address Bitcoin malware
X-BeenThere: bitcoin-development@lists.sourceforge.net
X-Mailman-Version: 2.1.9
Precedence: list
List-Id: <bitcoin-development.lists.sourceforge.net>
List-Unsubscribe: <https://lists.sourceforge.net/lists/listinfo/bitcoin-development>,
	<mailto:bitcoin-development-request@lists.sourceforge.net?subject=unsubscribe>
List-Archive: <http://sourceforge.net/mailarchive/forum.php?forum_name=bitcoin-development>
List-Post: <mailto:bitcoin-development@lists.sourceforge.net>
List-Help: <mailto:bitcoin-development-request@lists.sourceforge.net?subject=help>
List-Subscribe: <https://lists.sourceforge.net/lists/listinfo/bitcoin-development>,
	<mailto:bitcoin-development-request@lists.sourceforge.net?subject=subscribe>
X-List-Received-Date: Tue, 03 Feb 2015 00:41:15 -0000

This is an OpenPGP/MIME signed message (RFC 4880 and 3156)
--uTb2NBheAWRWCFahxfJP01PjuEUMw6UwL
Content-Type: text/plain; charset=utf-8
Content-Transfer-Encoding: quoted-printable

One clarification below.

e

On 02/02/2015 02:54 PM, Eric Voskuil wrote:
> On Feb 2, 2015, at 11:53 AM, Mike Hearn wrote:
>>
>> In sending the first-signed transaction to another for second
>> signature, how does the first signer authenticate to the second
>> without compromising the  independence of the two factors?
>>
>> Not sure what you mean. The idea is the second factor displays the
>> transaction and the user confirms it matches what they input to the
>> first factor. Ideally, using BIP70, but I don't know if BA actually
>> uses that currently.
>>
>> It's the same model as the TREZOR, except with a desktop app instead
>> of myTREZOR and a phone instead of a dedicated hardware device.=20
>=20
> Sorry for the slow reply, traveling.
>=20
> My comments were made in reference to this proposal:
>=20
>>> On Feb 2, 2015, at 10:40 AM, Brian Erdelyi <brian.erdelyi@gmail.com
>>> <mailto:brian.erdelyi@gmail.com>> wrote:
>>>
>>> Another concept...
>>>
>>> It should be possible to use multisig wallets to protect against
>>> malware.  For example, a user could generate a wallet with 3 keys and=

>>> require a transaction that has been signed by 2 of those keys.  One
>>> key is placed in cold storage and anther sent to a third-party.
>>>
>>> It is now possible to generate and sign transactions on the users
>>> computer and send this signed transaction to the third-party for the
>>> second signature.  This now permits the use of out of band transactio=
n
>>> verification techniques before the third party signs the transaction
>>> and sends to the blockchain.
>>>
>>> If the third-party is malicious or becomes compromised they would not=

>>> have the ability to complete transactions as they only have one
>>> private key.  If the third-party disappeared, the user could use the
>>> key in cold storage to sign transactions and send funds to a new wall=
et.
>>>
>>> Thoughts?

My comments below start out with the presumption of user platform
compromise, but the same analysis holds for the case where the user
platform is clean but a web wallet is compromised. Obviously the idea is
that either or both may be compromised, but integrity is retained as
long as both are not compromised and in collusion.

> In the multisig scenario the presumption is of a user platform
> compromised by malware. It envisions a user signing a 2 of 3 output wit=
h
> a first signature. The precondition that the platform is compromised
> implies that this process results in a loss of integrity of the private=

> key, and as such if it were not for the second signature requirement,
> the malware would be able to spend the output. This may be extended to
> all of the keys in the wallet.
>=20
> The scenario envisions sending the signed transaction to an another
> ("third") party. The objective is for the third party to provide the
> second signature, thereby spending the output as intended by the user,
> who is not necessarily the first signer. The send must be authenticated=

> to the user. Otherwise the third party would have to sign anything it
> received, obviously rendering the second signature pointless. This
> implies that the compromised platform must transmit a secret, or proof
> of a secret, to the third party.
>=20
> The problem is that the two secrets are not independent if the first
> platform is compromised. So of course the malware has the ability to
> sign, impersonate the user and send to the third party. So the third
> party *must* send the transaction to an *independent* platform for
> verification by the user, and obtain consent before adding the second
> signature. The user, upon receiving the transaction details, must be
> able to verify, on the independent platform, that the details match
> those of the transaction that user presumably signed. Even for simple
> transactions this must include amount, address and fees.
>=20
> The central assumptions are that, while the second user platform may be=

> compromised, the attack against the second platform is not coordinated
> with that of the first, nor is the third party in collusion with the
> first platform.
>=20
> Upon these assumptions rests the actual security benefit (increased
> difficulty of the coordinated attack). The strength of these assumption=
s
> is an interesting question, since it is hard to quantify. But without
> independence the entire security model is destroyed and there is thus n=
o
> protection whatsoever against malware.
>=20
> So for example a web-based or other third-party-provisioned
> implementation of the first platform breaks the anti-collusion
> assumption. Also, weak comsec allows an attack against the second
> platform to be carried out against its network. So for example a simple=

> SMS-based confirmation could be executed by the first platform alone an=
d
> thereby also break the the anti-collusion assumption. This is why I
> asked how independence is maintained.
>=20
> The assumption of a hardware wallet scenario is that the device itself
> is not compromised. So the scenario is not the same. If the user signs
> with a hardware wallet, nothing can collude with that process, with one=

> caveat.
>=20
> While a hardware wallet is not subject to onboard malware, it is not
> inconceivable that its keys could be extracted through probing or other=

> direct attack against the hardware. It's nevertheless an assumption of
> hardware wallets that these attacks require loss of the hardware.
> Physical possession constitutes compromise. So the collusion model with=

> a hardware wallet does exist, it just requires device possession.
> Depending on the implementation the extraction may require a non-trivia=
l
> amount of time and money.
>=20
> In a scenario where the user signs with HW, then sends the transaction
> to a third party for a second of three signatures, and finally to a
> second platform for user verification, a HW thief needs to collude with=

> the third party or the second platform before the owner becomes aware o=
f
> the theft (notifying the third party). This of course implies that
> keeping both the fist and second platforms in close proximity
> constitutes collusion from a physical security standpoint. This is
> probably sufficient justification for not implementing such a model,
> especially given the cost and complexity of stealing and cracking a
> well-designed device. A device backup would provide comparable time to
> recover with far less complexity (and loss of privacy).
>=20
> Incidentally the hardware wallet idea breaks down once any aspect of th=
e
> platform or network to which it connects must be trusted, so for these
> purposes I do not consider certain hybrid models as hardware wallets at=

> all. For example one such device trusts that the compromised computer
> does not carry out a MITM attack between the signing device and a share=
d
> secret entered in parts over time by the user. This reduces to a single=

> factor with no protection against a compromised platform.
>=20
> Of course these questions address integrity, not privacy. Use of a thir=
d
> party implies loss of privacy to that party, and with weak comsec to th=
e
> network. Similarly, use of hardware signing devices implies loss of
> privacy to the compromised platforms with which they exchange transacti=
ons.
>=20
> e


--uTb2NBheAWRWCFahxfJP01PjuEUMw6UwL
Content-Type: application/pgp-signature; name="signature.asc"
Content-Description: OpenPGP digital signature
Content-Disposition: attachment; filename="signature.asc"

-----BEGIN PGP SIGNATURE-----
Version: GnuPG v1

iQEcBAEBAgAGBQJU0BkwAAoJEDzYwH8LXOFO8qsH/jMXsGUvthRCzafM0XIVB5Mi
1t0KfjzmjWhR7/dmz3NY2JqmDFVKxQFCd/HhHHspyhT7jNc6T0EwTSbizRZbY9DA
79ii7gdZAx5B6Sv+pmzf9wakdXP+ho7NIR0uvFz6PXDxlM7fFNO6PJJmJFlY0PMi
QF0spQ0y4R5sbaN+5odioQPbNidDT4/AN+b7m+/wcXj4Fh0G/RwLbQ6DVQf31zKv
83tqUk8EDW4JdXLJ7jBw6JftgmfrtSHbLv/0m3usPNmOEhRps4wY+lH2ig9FFoMm
YfG36ov8+tX9lOsfgWvq3v9vFoiVfC+5CgetHBGU8VMVpJHKCcsIhzGYVrLk9Ko=
=uKb1
-----END PGP SIGNATURE-----

--uTb2NBheAWRWCFahxfJP01PjuEUMw6UwL--