1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
|
Received: from sog-mx-1.v43.ch3.sourceforge.com ([172.29.43.191]
helo=mx.sourceforge.net)
by sfs-ml-2.v29.ch3.sourceforge.com with esmtp (Exim 4.76)
(envelope-from <adam@cypherspace.org>) id 1W3lLl-0003e9-CD
for bitcoin-development@lists.sourceforge.net;
Thu, 16 Jan 2014 11:43:05 +0000
X-ACL-Warn:
Received: from mout.perfora.net ([74.208.4.195])
by sog-mx-1.v43.ch3.sourceforge.com with esmtps (TLSv1:RC4-SHA:128)
(Exim 4.76) id 1W3lLj-000647-Hq
for bitcoin-development@lists.sourceforge.net;
Thu, 16 Jan 2014 11:43:05 +0000
Received: from netbook (c107-70.i07-27.onvol.net [92.251.107.70])
by mrelay.perfora.net (node=mrus1) with ESMTP (Nemesis)
id 0Lm2Pp-1VU9Pa0PwH-00ZjQ5; Thu, 16 Jan 2014 06:42:53 -0500
Received: by netbook (Postfix, from userid 1000)
id 8EF482E283F; Thu, 16 Jan 2014 12:42:44 +0100 (CET)
Received: by flare (hashcash-sendmail, from uid 1000);
Thu, 16 Jan 2014 12:42:43 +0100
Date: Thu, 16 Jan 2014 12:42:42 +0100
From: Adam Back <adam@cypherspace.org>
To: Jeremy Spilman <jeremy@taplink.co>
Message-ID: <20140116114242.GA30432@netbook.cypherspace.org>
References: <CANEZrP0huBWqgvQik9Yc26Tu4CwR0VSXcfC+qfzsZqvoU4VJGA@mail.gmail.com>
<20140113133746.GI38964@giles.gnomon.org.uk>
<CANEZrP1KAVhi_-cxCYe0rR9LUSYJ8MyW8=6eSJZ65FeY5ZJNuQ@mail.gmail.com>
<20140114225321.GT38964@giles.gnomon.org.uk>
<CANAnSg0tH_bK_19rsRRHOeZgrGYeWMhW89fXPyS4DQGmS4r_7A@mail.gmail.com>
<CALimQCXgc0eXeOcqFGUaCpSF7gKEe87KzvLqHZwUysV3WyjjGw@mail.gmail.com>
<CAAS2fgShChAQryfUOBp60jB-zxn2tH986fu1HfT+LsNdBYnoYg@mail.gmail.com>
<CAJHLa0P5r2+kxy7w8G=h=TAhdk1jUoW5UOiv-euo47uQY0u9ZA@mail.gmail.com>
<20140115230901.GA25135@netbook.cypherspace.org>
<op.w9q85wkhyldrnw@laptop-air.hsd1.ca.comcast.net>
MIME-Version: 1.0
Content-Type: text/plain; charset=us-ascii; format=flowed
Content-Disposition: inline
In-Reply-To: <op.w9q85wkhyldrnw@laptop-air.hsd1.ca.comcast.net>
User-Agent: Mutt/1.5.21 (2010-09-15)
X-Hashcash: 1:20:140116:jeremy@taplink.co::sbT/LB1fql5x8tCx:00000000000000000000
0000000000000000000000000XDD
X-Hashcash: 1:20:140116:jgarzik@bitpay.com::K/iCAWXoqqX3kqC5:0000000000000000000
0000000000000000000000004L/M
X-Hashcash: 1:20:140116:bitcoin-development@lists.sourceforge.net::Mu0wJJ6mYhUzH
Hmg:000000000000000000002Kqg
X-Hashcash: 1:20:140116:adam@cypherspace.org::00fXrqCYw3FoWG3F:00000000000000000
0000000000000000000000001Ce7
X-Provags-ID: V02:K0:VwPg2+On5kD/xriPh5ukXQ6X2REXOGKnwD8u8v8V1ZD
tL+ngKdupGuDpRztyumUq0W8lWh/nGG6CLQFmkgEXqq+hA/6H0
JiDd2KCinGgT7AjLNNPxHDZ1UFN5ZkzMpadUIUYR8nOw+oZS3d
e3qrB3rTBUA/YGuyjSfLQ99L4OQ11eerSV2OqqKiAsv0RmEh8F
YPCIZPK/rnoZSqZVr7zykk8zFv8D7nvzw90XV/SNlBV7Pu979F
cUZna0hItr0MX2KNciPoJgyTRCUGr8Zj5PxMU78R0dmITUpCtf
hmZiV8JUWhrUUy3SYknoNJtgEjCd8Io3V+DZy+9Xz6eCzgTr1p
/pV7einTMXU1evdpoLCuCE7Js92ieFp11+Fe0/Vvh
X-Spam-Score: -0.0 (/)
X-Spam-Report: Spam Filtering performed by mx.sourceforge.net.
See http://spamassassin.org/tag/ for more details.
-0.0 RCVD_IN_DNSWL_NONE RBL: Sender listed at http://www.dnswl.org/,
no trust [74.208.4.195 listed in list.dnswl.org]
-0.0 SPF_HELO_PASS SPF: HELO matches SPF record
X-Headers-End: 1W3lLj-000647-Hq
Cc: "bitcoin-development@lists.sourceforge.net"
<bitcoin-development@lists.sourceforge.net>
Subject: Re: [Bitcoin-development] unlinakble static address? & spv-privacy
(Re: Stealth Addresses)
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: Thu, 16 Jan 2014 11:43:05 -0000
On Wed, Jan 15, 2014 at 05:02:10PM -0800, Jeremy Spilman wrote:
>The second pubKey is useful [...] even just being able to scan for
>transactions yourself without keeping bitcoin-encumbered private keys
>decrypted in memory.
Agreed.
>On Wed, 15 Jan 2014 15:09:01 -0800, Adam Back <adam@cypherspace.org> wrote:
>>But I think its moderately expensive for the full node because it has to
>>do a DH calculation per transaction and its not precomputable so there is
>>IO per query. (In the P version in fact only payments which are thereby
>>reconizable as unlinkable static need to be processed).
>
>And of course, if you have multiple reuseable addresses, then you're
>doing this calculation separately to check each one.
>
>So the load on a popular centralized service would be quite high,
>which you may consider a feature.
Well only a linear increase, which is not any kind of realistic security
defense for even an academic researcher analysing flows. More concern is
that it could be expensive enough discourage adoption by full-nodes as an
open/free service to support SPV clients in finding their reusable address
payments. Its possibly an I/O DoS multiplier: send requests to the full
nodes at a moderate network rate and and watch as its disk thrashes.
>But I think it's great people can choose how to trade privacy for
>computation/bandwidth however they want, and services can compete to
>offer monitoring for 0+ bit prefixes.
Its not a decision with user localised effect. If most users use it with
parameters giving high elimination probability, that affects everyone else's
privacy also. Also statistical effects are accumulative as more plausibly
related addresses are eliminated at each potentially linked transaction. I
think once the network flow analysis guys are done with incorporating it,
and if reusable addresses saw significant use, my prediction is the result
will be pretty close to privacy game over and it will undo most if not all
of the hard-won privacy benefit of CoinJoin. (Recalling CoinJoin is only
adding a bit or two of entropy per join, this elimination effect could
easily undo more than that).
>>(And also there is proposed a version of the prefix computed via
>>brute-force to make it somewhat stealthy still).
>
>I think in this case the hash grinding of the prefix would only being
>used if thats how transactions are being indexed. I don't think it
>adds any privacy, it's just added work we're forced to do in order
>for the prefix to work as designed.
The point of the stealth security objective is to avoid creating a new and
smaller anonymity set. If all reusable addresses are easily recognizable as
reusable, thats far more revealing and useful to the network flow analysis.
Adam
|