12020-03-05T00:17:23  <aj> itym "mallyability", and "tranzaxions" isn't a 1-char change :)
  22020-03-05T00:19:24  <aj> sipa: but if you set SIGHASH_MUST_BE_ALL_SEGWIT, that just means you have 0% chance of successful spend if some input is malleable, rather than x% where x is whatever the chance of malleation actually occuring is? is that actually helpful?
  32020-03-05T00:20:09  <sipa> aj: "one or more"
  42020-03-05T00:20:52  <aj> "ct"->"x" isn't a 1-char change though?
  52020-03-05T00:21:40  <aj> tranzaxxions maybe?
  62020-03-05T00:21:47  <aj> god that sounds cool
  72020-03-05T00:22:00  <sipa> i like it.
  82020-03-05T00:24:24  <aj> (hmm. if you prove that a theorem is equivalent to some axiom (ie {A,B,C} -> T, but {A,B,T} -> C also), does that make the theorem a trans-axiom?)
  92020-03-05T00:39:35  <aj> so i think the idea is, we have confirmed inputs A,B,..; I'm signing A with taproot, creating T which spends A,B,.., and I want to create a child tx S which spends T:0, but I can't do that safely if one of the inputs A,B,.. was non-segwit, because it's sig could change turning T into T' with a different txid.
 102020-03-05T00:40:40  <aj> but... if that's the case, I don't know what T's txid is in the first place until I see an initial signature for the non-segwit input (or the p2sh input even if it is segwit!) and once i've seen the signed tx to calculate the txid T, i'll know if those signatures were segwit or not
 112020-03-05T00:42:13  <roconnor> Usually you'd create T, create S, sign S, sign input A on T.
 122020-03-05T00:42:39  <aj> but i at least need all the p2sh scripts for T to be revealed before i can create S
 132020-03-05T00:44:00  <aj> (at which point i can observe whether T is all segwit or not, and abort if i'm unhappy)
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 152020-03-05T00:44:47  <roconnor> for p2sh inputs yes.  It's a good observation that the txid of T is creating committing to the sigscripts.
 162020-03-05T00:46:05  <roconnor> you can tell if thos sigscripts are of the empty shape or p2sh shape, but neither one of those facts commits to the UTXO being segwit or not.
 172020-03-05T00:46:39  <roconnor> *scriptsigs
 182020-03-05T00:47:03  <roconnor> I can never remember the terminology.
 192020-03-05T00:49:42  <aj> you only have to validate the p2sh hash not the full scriptsig (ie signature checking or actual logic) to check if things are segwit or not
 202020-03-05T00:50:37  <aj> (you need the scriptpubkey to validate against, but we commit to those anyway so you should have them)
 212020-03-05T00:52:29  <roconnor> AFAIU the concern is we don't have the scriptpubkeys.
 222020-03-05T00:53:31  <roconnor> (but maybe I'm wrong)
 232020-03-05T00:54:34  <roconnor> Isn't proving a scriptpubkey is belongs to an outpoint is tedious?
 242020-03-05T00:54:35  <aj> ah, you're right
 252020-03-05T00:57:01  <aj> i was thinking it was committed to directly via sha_prevouts/etc, but it's not
 262020-03-05T00:57:31  <roconnor> I mean, we could do that...
 272020-03-05T00:57:49  <sipa> in taproot sighash we commit to the sPK
 282020-03-05T00:57:58  <aj> our sPK, not the other sPKs
 292020-03-05T00:58:02  <sipa> but only the one being spent
 302020-03-05T00:58:04  <sipa> right
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 322020-03-05T01:00:00  <sipa> that's... not crazy
 332020-03-05T01:00:09  <sipa> we already commit to all input amounts
 342020-03-05T01:00:19  <sipa> we could as well commit to the entire utxos
 352020-03-05T01:01:03  <roconnor> hash each scriptpubkey and hash those hashes?
 362020-03-05T01:01:57  <sipa> just turn the hash-of-all-input-amounts-concatenated to hash-of-all-CTxOuts-being-spent-concatenated
 372020-03-05T01:02:13  <roconnor> oh right
 382020-03-05T01:02:29  <roconnor> well, that makes fee calculation kinda annoying.
 392020-03-05T01:02:39  <sipa> how so?
 402020-03-05T01:02:41  <roconnor> having to process all these scripts in the way.
 412020-03-05T01:03:00  <sipa> they don't affect fee calculation?
 422020-03-05T01:03:19  <roconnor> well the do affect verify that the hash commits to the alledged values.
 432020-03-05T01:03:31  <aj> if you just care about the fees, having to deal with a raw pay2multisig script as well as the 8 byte value could be obnoxious?
 442020-03-05T01:04:22  <sipa> roconnor: i don't understand how any of this is related to fee calculation
 452020-03-05T01:05:14  <aj> it's the fee commitment, not the calculation per se?
 462020-03-05T01:05:18  <roconnor> Today in taproot, to compute the fees you are signing you need to add up all the outputs and then have someone tell you all the input values, and then concatenate all the inputs values and compute the hash.
 472020-03-05T01:05:52  <sipa> ah
 482020-03-05T01:05:52  <roconnor> in your proposal you have to have someone tell you all the input values and all the script pubkeys, which are arbitrary long, and concatenate them all together and compute the hash.
 492020-03-05T01:06:07  <sipa> and you mean this would force signers to be told all prevout sPKs
 502020-03-05T01:06:44  <sipa> i see
 512020-03-05T01:07:00  <sipa> intermediary hashing may help
 522020-03-05T01:07:21  <roconnor> the hash of hashes lets you even check one scriptpubkey instead of all of them.
 532020-03-05T01:07:39  <roconnor> Although it seems in most cases you'd want to check all of them or none of them.
 542020-03-05T01:08:55  <aj> clearly this calls for a merkle sum tree of ctxouts-being-spent
 552020-03-05T01:09:47  <aj> (hmm, does everyone use "clearly" for "the following isn't clear at all", or was that unique to some random maths book i read back in the day?)
 562020-03-05T01:10:01  <roconnor> I use it that way.
 572020-03-05T01:10:34  <sipa> i think "Hence, ..." is clearer (pun intended)
 582020-03-05T01:11:06  <roconnor> I always thought it was a math joke from reading "clearly" in math proofs that are not clear at all.
 592020-03-05T01:11:35  <roconnor> so maybe it is a math thing?
 602020-03-05T01:11:56  <aj> math things are the best things
 612020-03-05T01:15:53  <sipa> how to find the mathematician in the room?
 622020-03-05T01:16:13  <sipa> yell out loud "Let epsilon be an arbitrary number smaller than 0"
 632020-03-05T01:16:51  <sipa> i'm sure you can find alternatives for other math domains
 642020-03-05T01:17:08  <roconnor> What are the current rules around p2sh-wrapped-segwit-Vn?  They are non-malleable but anyone can spend?
 652020-03-05T01:17:48  <sipa> by non-malleable you mean "txid does not commit to the witness" ?
 662020-03-05T01:17:59  <sipa> that's a vacuous statement i think if anyone can spend them :p
 672020-03-05T01:18:28  <roconnor> I mean that the scriptsig must be fixed but anyone can spend by submitting any witness value.
 682020-03-05T01:18:36  <sipa> correct
 692020-03-05T01:18:39  <sipa> also non-standard
 702020-03-05T01:18:57  <sipa> but valid with any witness by consensus (bip 341 does not affect their validity at all)
 712020-03-05T01:19:59  <roconnor> AFAICT signing the scriptpubkeys gives enough information to check if the txid is malleable or not.  I mean, it is a bit of a pain to check, but not signifcantly worse than other checks.
 722020-03-05T01:20:12  <roconnor> like the fee check.
 732020-03-05T01:23:25  <roconnor> assuming you have the p2sh scriptsigs, which are needed to compute the txid that you are trying to determine if it is malleable or not.
 742020-03-05T01:23:29  <instagibbs> roconnor, sorry if replaying the convo, but you'd still need things like redeemscripts
 752020-03-05T01:23:35  <instagibbs> ok
 762020-03-05T01:23:39  <instagibbs> jynx
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 782020-03-05T01:26:14  <instagibbs> it makes checking for native segwit outputs really easy, at least, if you're requiring that
 792020-03-05T01:31:37  <roconnor> segwit scriptpubkeys are all bounded in size, so you can immediately reject anyone trying to fill the scriptpubkeys with nonsense for those who are checking this malleability condition.
 802020-03-05T01:37:24  <instagibbs> wallets could reject as needed as well. PSBTs already carry all this info
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