Return-Path: Received: from smtp1.linuxfoundation.org (smtp1.linux-foundation.org [172.17.192.35]) by mail.linuxfoundation.org (Postfix) with ESMTPS id 87F2DCE0 for ; Wed, 27 Jun 2018 14:04:12 +0000 (UTC) X-Greylist: domain auto-whitelisted by SQLgrey-1.7.6 Received: from mail.sldev.cz (mail.sldev.cz [88.208.115.66]) by smtp1.linuxfoundation.org (Postfix) with ESMTPS id AC747334 for ; Wed, 27 Jun 2018 14:04:11 +0000 (UTC) Received: from localhost (localhost [127.0.0.1]) by mail.sldev.cz (Postfix) with ESMTP id 952BEE1045; Wed, 27 Jun 2018 14:04:09 +0000 (UTC) X-Virus-Scanned: Debian amavisd-new at mail.sldev.cz Received: from mail.sldev.cz ([127.0.0.1]) by localhost (mail.sldev.cz [127.0.0.1]) (amavisd-new, port 10024) with ESMTP id egyDHH9XCVK7; Wed, 27 Jun 2018 14:04:07 +0000 (UTC) Received: from [10.8.0.37] (unknown [10.8.0.37]) by mail.sldev.cz (Postfix) with ESMTPSA id C55BFE089A; Wed, 27 Jun 2018 14:04:07 +0000 (UTC) To: Pieter Wuille , Bitcoin Protocol Discussion References: <21a616f5-7a17-35b9-85ea-f779f20a6a2d@satoshilabs.com> <20180621195654.GC99379@coinkite.com> From: matejcik Openpgp: preference=signencrypt Autocrypt: addr=jan.matejek@satoshilabs.com; 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Linux x86_64; rv:52.0) Gecko/20100101 Thunderbird/52.8.0 MIME-Version: 1.0 In-Reply-To: Content-Type: multipart/signed; micalg=pgp-sha256; protocol="application/pgp-signature"; boundary="II4FQgAuV7wT60CmTj8pwTV6mwozOhK9R" X-Spam-Status: No, score=-1.9 required=5.0 tests=BAYES_00 autolearn=ham version=3.3.1 X-Spam-Checker-Version: SpamAssassin 3.3.1 (2010-03-16) on smtp1.linux-foundation.org X-Mailman-Approved-At: Wed, 27 Jun 2018 14:06:03 +0000 Subject: Re: [bitcoin-dev] BIP 174 thoughts X-BeenThere: bitcoin-dev@lists.linuxfoundation.org X-Mailman-Version: 2.1.12 Precedence: list List-Id: Bitcoin Protocol Discussion List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , X-List-Received-Date: Wed, 27 Jun 2018 14:04:12 -0000 This is an OpenPGP/MIME signed message (RFC 4880 and 3156) --II4FQgAuV7wT60CmTj8pwTV6mwozOhK9R Content-Type: multipart/mixed; boundary="bYfRIH8kq2E9gqQjByPtvonXCRdwMSyWm"; protected-headers="v1" From: matejcik To: Pieter Wuille , Bitcoin Protocol Discussion Message-ID: <881def14-696c-3207-cf6c-49f337ccf0d1@satoshilabs.com> Subject: Re: [bitcoin-dev] BIP 174 thoughts References: <21a616f5-7a17-35b9-85ea-f779f20a6a2d@satoshilabs.com> <20180621195654.GC99379@coinkite.com> In-Reply-To: --bYfRIH8kq2E9gqQjByPtvonXCRdwMSyWm Content-Type: text/plain; charset=utf-8 Content-Language: en-US Content-Transfer-Encoding: quoted-printable hello, On 26.6.2018 22:30, Pieter Wuille wrote: >> (Moreover, as I wrote previously, the Combiner seems like a weirdly >> placed role. I still don't see its significance and why is it importan= t >> to correctly combine PSBTs by agents that don't understand them. If yo= u >> have a usecase in mind, please explain. >=20 > Forward compatibility with new script types. A transaction may spend > inputs from different outputs, with different script types. Perhaps > some of these are highly specialized things only implemented by some > software (say HTLCs of a particular structure), in non-overlapping > ways where no piece of software can handle all scripts involved in a > single transaction. If Combiners cannot deal with unknown fields, they > won't be able to deal with unknown scripts. Record-based Combiners *can* deal with unknown fields. Either by including both versions, or by including one selected at random. This is the same in k-v model. > combining must be done independently by Combiner implementations for > each script type involved. As this is easily avoided by adding a > slight bit of structure (parts of the fields that need to be unique - > "keys"), this seems the preferable option. IIUC, you're proposing a "semi-smart Combiner" that understands and processes some fields but not others? That doesn't seem to change things. Either the "dumb" combiner throws data away before the "smart" one sees it, or it needs to include all of it anyway. > No, a Combiner can pick any of the values in case different PSBTs have > different values for the same key. That's the point: by having a > key-value structure the choice of fields can be made such that > Combiners don't need to care about the contents. Finalizers do need to > understand the contents, but they only operate once at the end. > Combiners may be involved in any PSBT passing from one entity to > another. Yes. Combiners don't need to care about the contents. So why is it important that a Combiner properly de-duplicates the case where keys are the same but values are different? This is a job that, AFAICT so far, can be safely left to someone along the chain who understands that particular record. Say we have field F(key,value), and several Signers produce F(1,1), F(1,2), F(1,3). A key-based Combiner will pick exactly one to pass along. A record-based Combiner will pass all three. It seems that you consider the latter PSBT "invalid". But it is well formed and doesn't contain duplicate records. A Finalizer, or a different Combiner that understands field F, can as well have the rule "throw away all but one" for this case. To repeat and restate my central question: Why is it important, that an agent which doesn't understand a particular field structure, can nevertheless make decisions about its inclusion or omission from the result (based on a repeated prefix)? Actually, I can imagine the opposite: having fields with same "key" (identifying data), and wanting to combine their "values" intelligently without losing any of the data. Say, two Signers producing separate parts of a combined-signature under the same common public key? > In case of BIP32 derivation, computing the pubkeys is possibly > expensive. A simple signer can choose to just sign with whatever keys > are present, but they're not the only way to implement a signer, and > even less the only software interacting with this format. Others may > want to use a matching approach to find keys that are relevant; > without pubkeys in the format, they're forced to perform derivations > for all keys present. I'm going to search for relevant keys by comparing master fingerprint; I would expect HWWs generally don't have index based on leaf pubkeys. OTOH, Signers with lots of keys probably aren't resource-constrained and can do the derivations in case of collisions. Also, you need to do the derivation and checking anyway, because what if there is a mismatch between the key and the value? I liked @achow101's idea about supporting non-derived keys, but I assumed that you would match them based on the master fingerprint too? I wouldn't be against including the full master public key (probably without chaincode) instead of the fingerprint, as you proposed earlier. But including both the leaf pubkey and the fingerprint seems weird. > If you take the records model, and then additionally drop the > whole-record uniqueness constraint, yes, though that seems pushing it > a bit by moving even more guarantees from the file format to > application level code. The "file format" makes no guarantees, because the parsing code and application code is the same anyway. You could say I'm proposing to separate these concerns ;) regards m. --bYfRIH8kq2E9gqQjByPtvonXCRdwMSyWm-- --II4FQgAuV7wT60CmTj8pwTV6mwozOhK9R Content-Type: application/pgp-signature; name="signature.asc" Content-Description: OpenPGP digital signature Content-Disposition: attachment; filename="signature.asc" -----BEGIN PGP SIGNATURE----- Version: GnuPG v2 iQIcBAEBCAAGBQJbM5lWAAoJEMZ/sQbk7RceV6AP/0+CJX6vojsoDxjHHMEWAo2J hQ0vo5OYGRCyuEs51ek9vCqgpM7iyzuqxzpPGmSetkfoMv2poQR4rnazPZ3WFnoG Gf1AY76wz2PINiwdvLfbPst+Iu41GGWt3Bf+ltc6Q0eW7JwTtOF0pjV2mzM4Q88I BYoU1IF+9O7EDTVMWLLl4L61T5TSB844nSucC574zekQvrTUl5X5MBHkgJUJPApQ 0eebqEz0eo+fvaTGFj2JxWeudMhYPyZ8oTm9wUh0kuIhyhejKT6kMgKtBGm4AR/G B2Gghpo8yyEGrP1s5+YAm0Cax6CIhEM9uDr5puqYfitEhz1/ZWzl+7ZwT/ds3k0/ 0sr/CikwBoZPECyRBDyaVGye70/1YWcAJmBqHiYMEOB7wg0VMAwH6aTaPB00aKg1 HwmtqlChHfTSHRbTXEBRcVmDiiVg8IEVAiv2rlGKvMNS0S/cy2XtUncBk1rhycXR +q2OHMT4pSNXLhWnreon9O83R+v0gEwGC+Qn2muRG9IL7B74L/10U1N1WCTMHfkp 1Bs9qYrH5Y9BFc+ZxLTbPxiLP3UrPME0yDsmUprTRt1tz7i1iydeZvHsTOQW4wlg iigvyMTJh8eiy1erD3OeAM10dVFzgAd3O4v5qvRie81RwYpwVNUNtBAsENyP8ghS +rcTFMI4J7XQiOWnybem =i5KP -----END PGP SIGNATURE----- --II4FQgAuV7wT60CmTj8pwTV6mwozOhK9R--