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
|
Return-Path: <vjudeu@gazeta.pl>
Received: from smtp1.osuosl.org (smtp1.osuosl.org [140.211.166.138])
by lists.linuxfoundation.org (Postfix) with ESMTP id 0D117C002D
for <bitcoin-dev@lists.linuxfoundation.org>;
Sat, 7 May 2022 04:50:22 +0000 (UTC)
Received: from localhost (localhost [127.0.0.1])
by smtp1.osuosl.org (Postfix) with ESMTP id 04113829AF
for <bitcoin-dev@lists.linuxfoundation.org>;
Sat, 7 May 2022 04:50:22 +0000 (UTC)
X-Virus-Scanned: amavisd-new at osuosl.org
X-Spam-Flag: NO
X-Spam-Score: -2.099
X-Spam-Level:
X-Spam-Status: No, score=-2.099 tagged_above=-999 required=5
tests=[BAYES_00=-1.9, DKIM_SIGNED=0.1, DKIM_VALID=-0.1,
DKIM_VALID_AU=-0.1, DKIM_VALID_EF=-0.1, FREEMAIL_FROM=0.001,
SPF_HELO_NONE=0.001, SPF_PASS=-0.001] autolearn=ham autolearn_force=no
Authentication-Results: smtp1.osuosl.org (amavisd-new);
dkim=pass (1024-bit key) header.d=gazeta.pl
Received: from smtp1.osuosl.org ([127.0.0.1])
by localhost (smtp1.osuosl.org [127.0.0.1]) (amavisd-new, port 10024)
with ESMTP id 4Iwx3_z5IFoe
for <bitcoin-dev@lists.linuxfoundation.org>;
Sat, 7 May 2022 04:50:21 +0000 (UTC)
X-Greylist: from auto-whitelisted by SQLgrey-1.8.0
Received: from smtpo92.poczta.onet.pl (smtpo92.poczta.onet.pl
[213.180.149.145])
by smtp1.osuosl.org (Postfix) with ESMTPS id B690882848
for <bitcoin-dev@lists.linuxfoundation.org>;
Sat, 7 May 2022 04:50:20 +0000 (UTC)
Received: from mta3.m5r2.onet (mta3.m5r2.onet [10.174.35.137])
by smtp.poczta.onet.pl (Onet) with ESMTP id 4KwFNh1yqpzlgBtL
for <bitcoin-dev@lists.linuxfoundation.org>;
Sat, 7 May 2022 06:50:12 +0200 (CEST)
DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=gazeta.pl; s=2013;
t=1651899012; bh=dZ+ZPHt/5thfWlbPpH0W7XeiwO90x0K8yx77yxoXypg=;
h=From:To:Subject:Date:From;
b=bSxUGKQGh5TDIlgAlxm0lYkGEMIzQx1Co0zvO7S0ihYca4uk9ucFIDpYaDL6sjYXN
u93brSVojFw5g5k1IvKhIPx0Z2iJG8pcjwhD1n1I1dK6+b4NPKwOvSPnT3QrqBgCA6
kM6RHkZ2EfWJ7SwEulkodXMAZ7Oqy9u+QAIBt9eY=
Content-Type: text/plain; charset=utf-8
X-Mailer: onet.poczta
X-Priority: 3
X-Onet-Pmq: <vjudeu@gazeta.pl>;5.173.233.66;PL;1
Received: from [5.173.233.66] by mta2.m5r2.onet with HTTP id
0809e15f2cfefe0b; Sat, 07 May 2022 06:50:12 +0200
From: vjudeu@gazeta.pl
To: bitcoin-dev@lists.linuxfoundation.org
Message-ID: <75be7180-709a-b735-a27b-50d0c6a2af5b@gazeta.pl>
Content-Transfer-Encoding: quoted-printable
Date: Sat, 07 May 2022 04:50:12 +0000
MIME-Version: 1.0
X-Mailman-Approved-At: Sat, 07 May 2022 08:54:25 +0000
Subject: [bitcoin-dev] Adding SIGHASH to TXID
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: Sat, 07 May 2022 04:50:22 -0000
For now, we have txid:vout as a previous transaction output. This means =
that to have a stable TXID, we are forced to use SIGHASH_ALL somewhere, =
just to prevent any transaction modifications that can happen during adding=
some inputs and outputs. But it seems that new sighashes could be far more=
powerful than we expected: it is technically possible to not only remove =
previous transaction output by using SIGHASH_ANYPREVOUT. We can do more and=
do it better, we could decide, how to calculate this txid at all!
So, something like SIGHASH_PREVOUT_NONE would be similar to SIGHASH_NONE =
(applied to the previous transaction, taken from txid). To have =
SIGHASH_ANYPREVOUT, we need to remove absolutely everything, I don't know =
any such sighashes, because even SIGHASH_NONE | SIGHASH_ANYONECANPAY will =
commit at least to some fields, for example to the locktime. But, if we =
introduce SIGHASH_PREVOUT_XYZ flags for all existing sighashes, we would =
have this:
SIGHASH_PREVOUT_NONE
SIGHASH_PREVOUT_SINGLE
SIGHASH_PREVOUT_ALL
SIGHASH_PREVOUT_ANYONECANPAY
Then, the procedure is as follows: we use =
txid:vout to find our previous transaction. Then, we apply those sighashes =
to this previous transaction, to form a new txid, that will be checked =
during every OP_CHECKSIG-based opcode. In this way, our txid:vout is used =
just to do transaction lookup, after that, sighashes can be applied to the =
previous transaction, so our txid could remain stable, even if someone will=
add some inputs and outputs.
By default, we could use SIGHASH_PREVOUT_ALL=
, that would mean our txid:vout remains unchanged. Then, =
SIGHASH_PREVOUT_SINGLE would obviously mean, that we want to commit only to=
this particular previous transaction output. That would allow adding any =
new outputs to the previous transaction, without affecting our replaced =
txid, but also without blindly accepting any txid, because some data of the=
previous transaction would be still hashed.
Then, SIGHASH_PREVOUT_NONE is=
an interesting case, because it would mean that no outputs of the previous=
transaction are checked. But still, the inputs will be! That would mean: =
"I don't care about in-between addresses, but I care that it was initiated =
from these inputs". In this case, it is possible to choose some input =
without those flags, and then apply SIGHASH_PREVOUT_NONE many times, to =
make sure that everything started from that input, but everything =
in-between can be anything.
All of those three SIGHASH_PREVOUT_XYZ flags =
could be combined with SIGHASH_PREVOUT_ANYONECANPAY. That would mean all =
inputs of the previous transaction are discarded, except from the input =
number matching "vout". Or we could just use SIGHASH_PREVOUT_ANY instead =
and discard all inputs from that previous transaction, that could also be =
combined with other sighashes.
So, to sum up, by applying sighashes to the=
previous transaction, instead of allowing for any transaction, we could =
still have some control of our txid, and I think it could be better than =
just saying "give me any txid, I will accept that". I think in most cases =
we don't want to allow any txid: we want to only "control the flow", just =
to make sure that our signatures will sign what we want and will not be =
invalidated by changing some transaction inputs and outputs, unrelated to =
the currently-checked signature.
|
