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
|
Return-Path: <dave@dtrt.org>
Received: from smtp4.osuosl.org (smtp4.osuosl.org [IPv6:2605:bc80:3010::137])
by lists.linuxfoundation.org (Postfix) with ESMTP id EA372C002D
for <bitcoin-dev@lists.linuxfoundation.org>;
Thu, 12 May 2022 07:17:09 +0000 (UTC)
Received: from localhost (localhost [127.0.0.1])
by smtp4.osuosl.org (Postfix) with ESMTP id D2CA540142
for <bitcoin-dev@lists.linuxfoundation.org>;
Thu, 12 May 2022 07:17:09 +0000 (UTC)
X-Virus-Scanned: amavisd-new at osuosl.org
X-Spam-Flag: NO
X-Spam-Score: -4.2
X-Spam-Level:
X-Spam-Status: No, score=-4.2 tagged_above=-999 required=5
tests=[BAYES_00=-1.9, RCVD_IN_DNSWL_MED=-2.3, RCVD_IN_MSPIKE_H3=0.001,
RCVD_IN_MSPIKE_WL=0.001, SPF_HELO_PASS=-0.001, SPF_PASS=-0.001]
autolearn=ham autolearn_force=no
Received: from smtp4.osuosl.org ([127.0.0.1])
by localhost (smtp4.osuosl.org [127.0.0.1]) (amavisd-new, port 10024)
with ESMTP id aJYHdzKT53px
for <bitcoin-dev@lists.linuxfoundation.org>;
Thu, 12 May 2022 07:17:08 +0000 (UTC)
X-Greylist: from auto-whitelisted by SQLgrey-1.8.0
Received: from smtpauth.rollernet.us (smtpauth.rollernet.us [208.79.240.5])
by smtp4.osuosl.org (Postfix) with ESMTPS id 9554440133
for <bitcoin-dev@lists.linuxfoundation.org>;
Thu, 12 May 2022 07:17:08 +0000 (UTC)
Received: from smtpauth.rollernet.us (localhost [127.0.0.1])
by smtpauth.rollernet.us (Postfix) with ESMTP id E951A280005E;
Thu, 12 May 2022 00:17:05 -0700 (PDT)
Received: from webmail.rollernet.us (webmail.rollernet.us
[IPv6:2607:fe70:0:14::a])
(using TLSv1.2 with cipher ECDHE-RSA-AES128-GCM-SHA256 (128/128 bits))
(Client did not present a certificate)
by smtpauth.rollernet.us (Postfix) with ESMTPSA;
Thu, 12 May 2022 00:17:05 -0700 (PDT)
MIME-Version: 1.0
Date: Wed, 11 May 2022 21:17:05 -1000
From: "David A. Harding" <dave@dtrt.org>
To: Greg Sanders <gsanders87@gmail.com>, Bitcoin Protocol Discussion
<bitcoin-dev@lists.linuxfoundation.org>
In-Reply-To: <CAB3F3Dtp7YQBhLJQbCLpSKau8Hj=5gN4yuGCFN=u=6e1o6o=dA@mail.gmail.com>
References: <CAB3F3Dtp7YQBhLJQbCLpSKau8Hj=5gN4yuGCFN=u=6e1o6o=dA@mail.gmail.com>
User-Agent: Roundcube Webmail/1.4.10
Message-ID: <6a73b36724e6134a1cd57ea9277f2779@dtrt.org>
X-Sender: dave@dtrt.org
Content-Type: text/plain; charset=US-ASCII;
format=flowed
Content-Transfer-Encoding: 7bit
X-Rollernet-Abuse: Contact abuse@rollernet.us to report. Abuse policy:
http://www.rollernet.us/policy
X-Rollernet-Submit: Submit ID 1d4c.627cb471.a3fde.0
Subject: Re: [bitcoin-dev] Bringing a nuke to a knife fight: Transaction
introspection to stop RBF pinning
X-BeenThere: bitcoin-dev@lists.linuxfoundation.org
X-Mailman-Version: 2.1.15
Precedence: list
List-Id: Bitcoin Protocol Discussion <bitcoin-dev.lists.linuxfoundation.org>
List-Unsubscribe: <https://lists.linuxfoundation.org/mailman/options/bitcoin-dev>,
<mailto:bitcoin-dev-request@lists.linuxfoundation.org?subject=unsubscribe>
List-Archive: <http://lists.linuxfoundation.org/pipermail/bitcoin-dev/>
List-Post: <mailto:bitcoin-dev@lists.linuxfoundation.org>
List-Help: <mailto:bitcoin-dev-request@lists.linuxfoundation.org?subject=help>
List-Subscribe: <https://lists.linuxfoundation.org/mailman/listinfo/bitcoin-dev>,
<mailto:bitcoin-dev-request@lists.linuxfoundation.org?subject=subscribe>
X-List-Received-Date: Thu, 12 May 2022 07:17:10 -0000
On 2022-05-10 08:53, Greg Sanders via bitcoin-dev wrote:
> We add OPTX_SELECT_WEIGHT(pushes tx weight to stack, my addition to
> the proposal) to the "state" input's script.
> This is used in the update transaction to set the upper bound on the
> final transaction weight.
> In this same input, for each contract participant, we also
> conditionally commit to the change output's scriptpubkey
> via OPTX_SELECT_OUTPUT_SCRIPTPUBKEY and OPTX_SELECT_OUTPUTCOUNT==2.
> This means any participant can send change back
> to themselves, but with a catch. Each change output script possibility
> in that state input also includes a 1 block
> CSV to avoid mempool spending to reintroduce pinning.
I like the idea! However, I'm not sure the `1 CSV` trick helps much.
Can't an attacker just submit to the mempool their other eltoo state
updates? For example, let's assume Bob and Mallory have a channel with
>25 updates and Mallory wants to prevent update[-1] from being committed onchain before its (H|P)TLC timeout. Mallory also has at least 25 unencumbered UTXOs, so she submits to the mempool update[0], update[1], update[...], update[24]---each of them with a different second input to pay fees.
If `OPTX_SELECT_WEIGHT OP_TX` limits each update's weight to 1,000
vbytes[1] and the default node relay/mempool policy of allowing a
transaction and up to 24 descendants remains, Mallory can pin the
unsubmitted update[-1] under 25,000 vbytes of junk---which is 25% of
what she can pin under current mempool policies.
Alice can't RBF update[0] without paying for update[1..24] (BIP125 rule
#3), and an RBF of update[24] will have its additional fees divided by
its size plus the 24,000 vbytes of update[1..24].
To me, that seems like your proposal makes escaping the pinning at most
75% cheaper than today. That's certainly an improvement---yay!---but
I'm not sure it eliminates the underlying concern. Also depending on
the mempool ancestor/descendant limits makes it harder to raise those
limits in the future, which is something I think we might want to do if
we can ensure raising them won't increase node memory/CPU DoS risk.
I'd love to hear that my analysis is missing something though!
Thanks!,
-Dave
[1] 1,000 vbytes per update seems like a reasonable value to me.
Obviously there's a tradeoff here: making it smaller limits the amount
of pinning possible (assuming mempool ancestor/descendant limits remain)
but also limits the number and complexity of inputs that may be added.
I don't think we want to discourage people too much from holding
bitcoins in deep taproot trees or sophisticated tapscripts.
|
