watch only multisig scripts require pubkeys to be imported to flag them solvable

jonasschnelli commented at 10:27 am on October 6, 2018: contributor

Use case: decouple keys from the wallet (via importing scripts and fundrawtransaction with watch-only).

Problem: multisig inputs are flagged as non-spendable even if importing both the multisig P2SH scriptPubKey and the redeemScript (via importmulti).

The current isSolveable() logic calls GetPubKey() and only flags them as solvable if the pubkeys are in the wallet.

Expected behaviour:

multisig Inputs should be flagged as solvable (and therefore usable via fundrawtransaction) when importing the P2(W)SH scriptPubKey and the redeemScripts

Current workaround:

Call importpubkey for all pubkeys used in the multisig (redeemScript). importpubkey derives all coming scripts (including a raw P2PK script). The P2PK scripts make the wallet store the pubkey and flag the multisig script solvable.

jonasschnelli added the label Bug on Oct 6, 2018

jonasschnelli added the label Wallet on Oct 6, 2018

jonasschnelli commented at 10:28 am on October 6, 2018: contributor

IRC discussion:

 0[12:06:00]  <jonasschnelli>	The only way how to import a watch only multisig is by importing the outer script, the readme-script and all it's pubkeys (via importpubkey)
 1[12:06:30]  <sipa>	you don't need the pubkeys for multisig
 2[12:06:34]  <sipa>	only for p2pkh
 3[12:06:51]  <jonasschnelli>	sipa:If you don't import the pubkey they are non-solvable and not useable in fundraw
 4[12:07:06]  <jonasschnelli>	So you need to import via importpubkey (and import all possible scripts!)
 5[12:07:28]  <sipa>	jonasschnelli: that makes no sense
 6[12:07:31]  <jonasschnelli>	GetScriptForRawPubKey will then lead to extract the pubKey and place them mapWatchKeys
 7[12:07:43]  <jonasschnelli>	Agree it makes no sense...
 8[12:07:55]  <sipa>	importing a pubkey is so that the signing code can find the pubkey based on the hash of the key
 9[12:08:03]  <sipa>	in a multisig there are no key hashes involved
10[12:08:13]  <sipa>	just the redeemscript should be enough for multisig
11[12:08:39]  <sipa>	plus importaddress of the toplevel thing
12[12:08:43]  <jonasschnelli>	Yes. But following isSolvable, it will require to find the pubkey in oder to flag it solveable
13[12:09:00]  <sipa>	it has the pubkey; it's in the redeemscript
14[12:09:06]  <sipa>	i'm very skeptical :)
15[12:09:11]  <jonasschnelli>	but it won't find it...
16[12:09:19]  <sipa>	have you tried this?
17[12:09:29]  <jonasschnelli>	Yes
18[12:09:32]  <sipa>	i find this very hard to believe
19[12:09:37]  <jonasschnelli>	mapWatchKeys gets only touched by AddWatchOnly
20[12:09:44]  <jonasschnelli>	Try yourself... with the following steps:
21[12:09:49]  <jonasschnelli>	1. createwallet "dummy" true
22[12:09:53]  <sipa>	what do you need mapWatchKeys for in multisig?
23[12:09:54] 	escrivner (~user@cpe-76-175-74-114.socal.res.rr.com) left IRC (Ping timeout: 252 seconds)
24[12:10:37]  <jonasschnelli>	sipa: pure watching no,.. but if you want to use them for watchOnly coinselection via fundraw, yes, you need it with the corrent code
25[12:10:47]  <sipa>	that makes no sense :)
26[12:10:55]  <sipa>	if you say so, i believe you
27[12:11:01]  <sipa>	bit i don't know what that is the case
28[12:11:03]  <jonasschnelli>	Try it youself. :)
29[12:11:09]  <sipa>	i can't right now
30[12:11:16]  <jonasschnelli>	Sure. No hurry...
31[12:11:24]  <jonasschnelli>	the use case: decouple the keys from the wallet
32[12:11:44]  <jonasschnelli>	(via importing scripts and using fundrawtransaction)
33[12:11:44]  <sipa>	yes not claiming this isn't important!
34[12:11:57]  <sipa>	i'm just not understanding why you need to import the pubkeys
35[12:12:06]  <sipa>	they are in the redeemscript
36[12:12:28]  <sipa>	the signing code doesn't need to look up any pubkeys
37[12:12:45]  <jonasschnelli>	Because: fundraw takes only solvable imputs. isSolveable requires to find the pubKey in the keystore.
38[12:12:53]  <jonasschnelli>	But it's fixable IMO
39[12:12:54]  <sipa>	why?
40[12:13:23]  <jonasschnelli>	isSolveable _currently_ requires to find the pubKey... its just coded that way...
41[12:13:50]  <sipa>	can you point me to the code?
42[12:14:01]  <jonasschnelli>	1s..
43[12:14:49]  <jonasschnelli>	code part 1: https://github.com/bitcoin/bitcoin/blob/master/src/script/sign.cpp#L141
44[12:15:36]  <sipa>	sure, but that doesn't need the pubkey imported, only the redeemscript
45[12:16:25]  <jonasschnelli>	code part 2: https://github.com/bitcoin/bitcoin/blob/aa39ca764578a9017e03796b554955796022eb0d/src/script/sign.cpp#L84
46[12:16:31]  <jonasschnelli>	(GetPubKey(provider, sigdata, keyid, pubkey);)
47[12:16:46]  <jonasschnelli>	Goes into: bool CCryptoKeyStore::GetPubKey(const CKeyID &address, CPubKey& vchPubKeyOut) const
48[12:16:51]  <sipa>	oh
49[12:16:55]  <sipa>	you're right
50[12:16:56] 	phwalkr (~phwalkr@194.210.91.110) left IRC (Remote host closed the connection)
51[12:17:03]  <sipa>	that's stupid :)
52[12:17:08]  <jonasschnelli>	yes... it's a mess
53[12:17:30] sipa	quietly mentions descriptors again
54[12:17:44]  <jonasschnelli>	Indeed!
55[12:17:47] 	escrivner (~user@cpe-76-175-74-114.socal.res.rr.com) joined the channel
56[12:18:23]  <jonasschnelli>	You can bypass that problem by importpubkey all the multisigs pubkeys because it will generate a RawPubKeyScript where the pubkeys gets extracted and added to the keystore. :/
57[12:18:36]  <jonasschnelli>	(with an overhead of a couple of unused scripts)
58[12:18:48]  <sipa>	yeah
59[12:18:56]  <sipa>	but that's pretty ridiculous

jonasschnelli commented at 10:51 am on October 6, 2018: contributor

Seems to be a 0.17 regression (just tested on 0.16.3 and seems that the inputs there are marked as solvable).

jonasschnelli referenced this in commit 2a2cac7873 on Oct 15, 2018

Sjors commented at 8:32 am on October 17, 2018: member

@jonasschnelli this is fixed, right?

achow101 commented at 3:18 pm on November 8, 2018: member

Since #14424 was merged, this can be closed now.

MarcoFalke closed this on Nov 8, 2018

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watch only multisig scripts require pubkeys to be imported to flag them solvable #14415