Return-Path: <jlrubin@mit.edu> Received: from smtp1.linuxfoundation.org (smtp1.linux-foundation.org [172.17.192.35]) by mail.linuxfoundation.org (Postfix) with ESMTPS id B118E105B; Fri, 4 Oct 2019 05:02:30 +0000 (UTC) X-Greylist: domain auto-whitelisted by SQLgrey-1.7.6 X-Greylist: domain auto-whitelisted by SQLgrey-1.7.6 Received: from outgoing.mit.edu (outgoing-auth-1.mit.edu [18.9.28.11]) by smtp1.linuxfoundation.org (Postfix) with ESMTPS id 00EFEA8; Fri, 4 Oct 2019 05:02:28 +0000 (UTC) Received: from mail-io1-f49.google.com (mail-io1-f49.google.com [209.85.166.49]) (authenticated bits=0) (User authenticated as jlrubin@ATHENA.MIT.EDU) by outgoing.mit.edu (8.14.7/8.12.4) with ESMTP id x9452Qoa030285 (version=TLSv1/SSLv3 cipher=AES128-GCM-SHA256 bits=128 verify=NOT); Fri, 4 Oct 2019 01:02:27 -0400 Received: by mail-io1-f49.google.com with SMTP id n197so10750982iod.9; Thu, 03 Oct 2019 22:02:27 -0700 (PDT) X-Gm-Message-State: APjAAAUdxtBMvCJA4Le/V37GyRZRHvChHqFC4/1BmFoYTn4f712lsk6E SVPvdD4CgHdCd8MQ6va8zrFMvJgfoURfnytScqU= X-Google-Smtp-Source: APXvYqxX4wp0qdK3i3VD9SOxl3VOXCVlx92+opnaNo8l4Jj3R73TsuKJFt7wqLCzF3BUrMw6mlEOHyEG07SINCvMia8= X-Received: by 2002:a5e:8902:: with SMTP id k2mr11708140ioj.49.1570165346480; Thu, 03 Oct 2019 22:02:26 -0700 (PDT) MIME-Version: 1.0 References: <87wodp7w9f.fsf@gmail.com> <20191001155929.e2yznsetqesx2jxo@erisian.com.au> <CR-etCjXB-JWkvecjDog4Pkq1SuLUgndtSrZo-V4f4EGcNXzNCeAHRvCZGrxDWw7aHVdDY0pAF92jNLb_Hct0bMb3ew6JEpB9AfIm1tSGaQ=@protonmail.com> <CAEM=y+XbP3Dn7X8rHu7h0vbX6DkKA0vFK5nQqzcJ_V+D4EVMmw@mail.gmail.com> <C1OLL5FLxdOgfQ_A15mf88wIyztDapkyXJ2HZ0HxwmQADhRXGRe3le7Veso4tMIlbis6I0qiCd22xug5_GCKtgrjGnBtojWxOCMgn1UldkE=@protonmail.com> <CAEM=y+WCGSF_=WXpgXJUZCZcGUQhxzXF6Wv1_iX+VwEyYSWypg@mail.gmail.com> In-Reply-To: <CAEM=y+WCGSF_=WXpgXJUZCZcGUQhxzXF6Wv1_iX+VwEyYSWypg@mail.gmail.com> From: Jeremy <jlrubin@mit.edu> Date: Thu, 3 Oct 2019 22:02:14 -0700 X-Gmail-Original-Message-ID: <CAD5xwhi7=5eiv1jjf72-rUezZMfj3caR+PGfZEa8i8rjNjodFg@mail.gmail.com> Message-ID: <CAD5xwhi7=5eiv1jjf72-rUezZMfj3caR+PGfZEa8i8rjNjodFg@mail.gmail.com> To: Ethan Heilman <eth3rs@gmail.com> Content-Type: multipart/alternative; boundary="000000000000b73a1105940e9b4e" X-Spam-Status: No, score=-4.2 required=5.0 tests=BAYES_00,HTML_MESSAGE, RCVD_IN_DNSWL_MED autolearn=ham version=3.3.1 X-Spam-Checker-Version: SpamAssassin 3.3.1 (2010-03-16) on smtp1.linux-foundation.org Cc: ZmnSCPxj via bitcoin-dev <bitcoin-dev@lists.linuxfoundation.org>, "lightning-dev@lists.linuxfoundation.org" <lightning-dev@lists.linuxfoundation.org> Subject: Re: [bitcoin-dev] [Lightning-dev] OP_CAT was Re: Continuing the discussion about noinput / anyprevout X-BeenThere: bitcoin-dev@lists.linuxfoundation.org X-Mailman-Version: 2.1.12 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: Fri, 04 Oct 2019 05:02:30 -0000 --000000000000b73a1105940e9b4e Content-Type: text/plain; charset="UTF-8" Awhile back, Ethan and I discussed having, rather than OP_CAT, an OP_SHA256STREAM that uses the streaming properties of a SHA256 hash function to allow concatenation of an unlimited amount of data, provided the only use is to hash it. You can then use it perhaps as follows: // start a new hash with item OP_SHA256STREAM (-1) -> [state] // Add item to the hash in state OP_SHA256STREAM n [item] [state] -> [state] // Finalize OP_SHA256STREAM (-2) [state] -> [Hash] <-1> OP_SHA256STREAM <tag> <subnode 2> <subnode 3> <3> OP_SHA256STREAM <-2> OP_SHA256STREAM Or it coul -- @JeremyRubin <https://twitter.com/JeremyRubin> <https://twitter.com/JeremyRubin> On Thu, Oct 3, 2019 at 8:04 PM Ethan Heilman <eth3rs@gmail.com> wrote: > I hope you are having an great afternoon ZmnSCPxj, > > You make an excellent point! > > I had thought about doing the following to tag nodes > > || means OP_CAT > > `node = SHA256(type||SHA256(data))` > so a subnode would be > `subnode1 = SHA256(1||SHA256(subnode2||subnode3))` > and a leaf node would be > `leafnode = SHA256(0||SHA256(leafdata))` > > Yet, I like your idea better. Increasing the size of the two inputs to > OP_CAT to be 260 Bytes each where 520 Bytes is the maximum allowable > size of object on the stack seems sensible and also doesn't special > case the logic of OP_CAT. > > It would also increase performance. SHA256(tag||subnode2||subnode3) > requires 2 compression function calls whereas > SHA256(1||SHA256(subnode2||subnode3)) requires 2+1=3 compression > function calls (due to padding). > > >Or we could implement tagged SHA256 as a new opcode... > > I agree that tagged SHA256 as an op code that would certainty be > useful, but OP_CAT provides far more utility and is a simpler change. > > Thanks, > Ethan > > On Thu, Oct 3, 2019 at 7:42 PM ZmnSCPxj <ZmnSCPxj@protonmail.com> wrote: > > > > Good morning Ethan, > > > > > > > To avoid derailing the NO_INPUT conversation, I have changed the > > > subject to OP_CAT. > > > > > > Responding to: > > > """ > > > > > > - `SIGHASH` flags attached to signatures are a misdesign, sadly > > > retained from the original BitCoin 0.1.0 Alpha for Windows design, > on > > > par with: > > > [..] > > > > > > - `OP_CAT` and `OP_MULT` and `OP_ADD` and friends > > > [..] > > > """ > > > > > > OP_CAT is an extremely valuable op code. I understand why it was > > > removed as the situation at the time with scripts was dire. However > > > most of the protocols I've wanted to build on Bitcoin run into the > > > limitation that stack values can not be concatenated. For instance > > > TumbleBit would have far smaller transaction sizes if OP_CAT was > > > supported in Bitcoin. If it happens to me as a researcher it is > > > probably holding other people back as well. If I could wave a magic > > > wand and turn on one of the disabled op codes it would be OP_CAT. > Of > > > course with the change that size of each concatenated value must > be 64 > > > Bytes or less. > > > > Why 64 bytes in particular? > > > > It seems obvious to me that this 64 bytes is most suited for building > Merkle trees, being the size of two SHA256 hashes. > > > > However we have had issues with the use of Merkle trees in Bitcoin > blocks. > > Specifically, it is difficult to determine if a hash on a Merkle node is > the hash of a Merkle subnode, or a leaf transaction. > > My understanding is that this is the reason for now requiring > transactions to be at least 80 bytes. > > > > The obvious fix would be to prepend the type of the hashed object, i.e. > add at least one byte to determine this type. > > Taproot for example uses tagged hash functions, with a different tag for > leaves, and tagged hashes are just > prepend-this-32-byte-constant-twice-before-you-SHA256. > > > > This seems to indicate that to check merkle tree proofs, an `OP_CAT` > with only 64 bytes max output size would not be sufficient. > > > > Or we could implement tagged SHA256 as a new opcode... > > > > Regards, > > ZmnSCPxj > > > > > > > > > > On Tue, Oct 1, 2019 at 10:04 PM ZmnSCPxj via bitcoin-dev > > > bitcoin-dev@lists.linuxfoundation.org wrote: > > > > > > > > > > Good morning lists, > > > > Let me propose the below radical idea: > > > > > > > > - `SIGHASH` flags attached to signatures are a misdesign, sadly > retained from the original BitCoin 0.1.0 Alpha for Windows design, on par > with: > > > > - 1 RETURN > > > > - higher-`nSequence` replacement > > > > - DER-encoded pubkeys > > > > - unrestricted `scriptPubKey` > > > > - Payee-security-paid-by-payer (i.e. lack of P2SH) > > > > - `OP_CAT` and `OP_MULT` and `OP_ADD` and friends > > > > - transaction malleability > > > > - probably many more > > > > > > > > So let me propose the more radical excision, starting with SegWit v1: > > > > > > > > - Remove `SIGHASH` from signatures. > > > > - Put `SIGHASH` on public keys. > > > > > > > > Public keys are now encoded as either 33-bytes (implicit > `SIGHASH_ALL`) or 34-bytes (`SIGHASH` byte, followed by pubkey type, > followed by pubkey coordinate). > > > > `OP_CHECKSIG` and friends then look at the public key to determine > sighash algorithm rather than the signature. > > > > As we expect public keys to be indirectly committed to on every > output `scriptPubKey`, this is automatically output tagging to allow > particular `SIGHASH`. > > > > However, we can then utilize the many many ways to hide public keys > away until they are needed, exemplified in MAST-inside-Taproot. > > > > I propose also the addition of the opcode: > > > > > > > > <sighash> <pubkey> OP_SETPUBKEYSIGHASH > > > > > > > > > > > > - `sighash` must be one byte. > > > > - `pubkey` may be the special byte `0x1`, meaning "just use the > Taproot internal pubkey". > > > > - `pubkey` may be 33-byte public key, in which case the `sighash` > byte is just prepended to it. > > > > - `pubkey` may be 34-byte public key with sighash, in which case > the first byte is replaced with `sighash` byte. > > > > - If `sighash` is `0x00` then the result is a 33-byte public key > (the sighash byte is removed) i.e. `SIGHASH_ALL` implicit. > > > > > > > > This retains the old feature where the sighash is selected at > time-of-spending rather than time-of-payment. > > > > This is done by using the script: > > > > > > > > <pubkey> OP_SETPUBKEYSIGHASH OP_CHECKSIG > > > > > > > > > > > > Then the sighash can be put in the witness stack after the > signature, letting the `SIGHASH` flag be selected at time-of-signing, but > only if the SCRIPT specifically is formed to do so. > > > > This is malleability-safe as the signature still commits to the > `SIGHASH` it was created for. > > > > However, by default, public keys will not have an attached `SIGHASH` > byte, implying `SIGHASH_ALL` (and disallowing-by-default non-`SIGHASH_ALL`). > > > > This removes the problems with `SIGHASH_NONE` `SIGHASH_SINGLE`, as > they are allowed only if the output specifically says they are allowed. > > > > Would this not be a superior solution? > > > > Regards, > > > > ZmnSCPxj > > > > > > > > bitcoin-dev mailing list > > > > bitcoin-dev@lists.linuxfoundation.org > > > > https://lists.linuxfoundation.org/mailman/listinfo/bitcoin-dev > > > > > > Lightning-dev mailing list > > > Lightning-dev@lists.linuxfoundation.org > > > https://lists.linuxfoundation.org/mailman/listinfo/lightning-dev > > > > > _______________________________________________ > Lightning-dev mailing list > Lightning-dev@lists.linuxfoundation.org > https://lists.linuxfoundation.org/mailman/listinfo/lightning-dev > --000000000000b73a1105940e9b4e Content-Type: text/html; charset="UTF-8" Content-Transfer-Encoding: quoted-printable <div dir=3D"ltr"><div class=3D"gmail_default" style=3D"font-family:arial,he= lvetica,sans-serif;font-size:small;color:#000000">Awhile back, Ethan and I = discussed having, rather than OP_CAT, an OP_SHA256STREAM that uses the stre= aming properties of a SHA256 hash function to allow concatenation of an unl= imited amount of data, provided the only use is to hash it.</div><div class= =3D"gmail_default" style=3D"font-family:arial,helvetica,sans-serif;font-siz= e:small;color:#000000"><br></div><div class=3D"gmail_default" style=3D"font= -family:arial,helvetica,sans-serif;font-size:small;color:#000000">You can t= hen use it perhaps as follows:</div><div class=3D"gmail_default" style=3D"f= ont-family:arial,helvetica,sans-serif;font-size:small;color:#000000"><br></= div><div class=3D"gmail_default" style=3D"font-family:arial,helvetica,sans-= serif;font-size:small;color:#000000">// start a new hash with item<br></div= ><div class=3D"gmail_default" style=3D"font-family:arial,helvetica,sans-ser= if;font-size:small;color:#000000">OP_SHA256STREAM=C2=A0 (-1) -> [state]<= /div><div class=3D"gmail_default" style=3D"font-family:arial,helvetica,sans= -serif;font-size:small;color:#000000">// Add item to the hash in state<br><= /div><div class=3D"gmail_default" style=3D"font-family:arial,helvetica,sans= -serif;font-size:small;color:#000000">OP_SHA256STREAM n [item] [state] -&g= t; [state]</div><div class=3D"gmail_default" style=3D"font-family:arial,hel= vetica,sans-serif;font-size:small;color:#000000">// Finalize</div><div clas= s=3D"gmail_default" style=3D"font-family:arial,helvetica,sans-serif;font-si= ze:small;color:#000000">OP_SHA256STREAM (-2) [state] -> [Hash]</div><div= class=3D"gmail_default" style=3D"font-family:arial,helvetica,sans-serif;fo= nt-size:small;color:#000000"><br></div><div class=3D"gmail_default" style= =3D"font-family:arial,helvetica,sans-serif;font-size:small;color:#000000">&= lt;-1> OP_SHA256STREAM <tag> <subnode 2> <subnode 3> &= lt;3> OP_SHA256STREAM <-2> OP_SHA256STREAM</div><div class=3D"gmai= l_default" style=3D"font-family:arial,helvetica,sans-serif;font-size:small;= color:#000000"><br></div><div class=3D"gmail_default" style=3D"font-family:= arial,helvetica,sans-serif;font-size:small;color:#000000"><br></div><div cl= ass=3D"gmail_default" style=3D"font-family:arial,helvetica,sans-serif;font-= size:small;color:#000000">Or it coul<br></div><div class=3D"gmail_default" = style=3D"font-family:arial,helvetica,sans-serif;font-size:small;color:#0000= 00"><br></div><div class=3D"gmail_default" style=3D"font-family:arial,helve= tica,sans-serif;font-size:small;color:#000000"><br></div><div class=3D"gmai= l_default" style=3D"font-family:arial,helvetica,sans-serif;font-size:small;= color:#000000"><br clear=3D"all"></div><div><div dir=3D"ltr" class=3D"gmail= _signature" data-smartmail=3D"gmail_signature"><div dir=3D"ltr">--<br><a hr= ef=3D"https://twitter.com/JeremyRubin" target=3D"_blank">@JeremyRubin</a><a= href=3D"https://twitter.com/JeremyRubin" target=3D"_blank"></a></div></div= ></div><br></div><br><div class=3D"gmail_quote"><div dir=3D"ltr" class=3D"g= mail_attr">On Thu, Oct 3, 2019 at 8:04 PM Ethan Heilman <<a href=3D"mail= to:eth3rs@gmail.com">eth3rs@gmail.com</a>> wrote:<br></div><blockquote c= lass=3D"gmail_quote" style=3D"margin:0px 0px 0px 0.8ex;border-left:1px soli= d rgb(204,204,204);padding-left:1ex">I hope you are having an great afterno= on ZmnSCPxj,<br> <br> You make an excellent point!<br> <br> I had thought about doing the following to tag nodes<br> <br> || means OP_CAT<br> <br> `node =3D SHA256(type||SHA256(data))`<br> so a subnode would be<br> `subnode1 =3D SHA256(1||SHA256(subnode2||subnode3))`<br> and a leaf node would be<br> `leafnode =3D SHA256(0||SHA256(leafdata))`<br> <br> Yet, I like your idea better. Increasing the size of the two inputs to<br> OP_CAT to be 260 Bytes each where 520 Bytes is the maximum allowable<br> size of object on the stack seems sensible and also doesn't special<br> case the logic of OP_CAT.<br> <br> It would also increase performance. SHA256(tag||subnode2||subnode3)<br> requires 2 compression function calls whereas<br> SHA256(1||SHA256(subnode2||subnode3)) requires 2+1=3D3 compression<br> function calls (due to padding).<br> <br> >Or we could implement tagged SHA256 as a new opcode...<br> <br> I agree that tagged SHA256 as an op code that would certainty be<br> useful, but OP_CAT provides far more utility and is a simpler change.<br> <br> Thanks,<br> Ethan<br> <br> On Thu, Oct 3, 2019 at 7:42 PM ZmnSCPxj <<a href=3D"mailto:ZmnSCPxj@prot= onmail.com" target=3D"_blank">ZmnSCPxj@protonmail.com</a>> wrote:<br> ><br> > Good morning Ethan,<br> ><br> ><br> > > To avoid derailing the NO_INPUT conversation, I have changed the<= br> > > subject to OP_CAT.<br> > ><br> > > Responding to:<br> > > """<br> > ><br> > > -=C2=A0 =C2=A0`SIGHASH` flags attached to signatures are a misdes= ign, sadly<br> > >=C2=A0 =C2=A0 =C2=A0retained from the original BitCoin 0.1.0 Alpha= for Windows design, on<br> > >=C2=A0 =C2=A0 =C2=A0par with:<br> > >=C2=A0 =C2=A0 =C2=A0[..]<br> > ><br> > > -=C2=A0 =C2=A0`OP_CAT` and `OP_MULT` and `OP_ADD` and friends<br> > >=C2=A0 =C2=A0 =C2=A0[..]<br> > >=C2=A0 =C2=A0 =C2=A0"""<br> > ><br> > >=C2=A0 =C2=A0 =C2=A0OP_CAT is an extremely valuable op code. I und= erstand why it was<br> > >=C2=A0 =C2=A0 =C2=A0removed as the situation at the time with scri= pts was dire. However<br> > >=C2=A0 =C2=A0 =C2=A0most of the protocols I've wanted to build= on Bitcoin run into the<br> > >=C2=A0 =C2=A0 =C2=A0limitation that stack values can not be concat= enated. For instance<br> > >=C2=A0 =C2=A0 =C2=A0TumbleBit would have far smaller transaction s= izes if OP_CAT was<br> > >=C2=A0 =C2=A0 =C2=A0supported in Bitcoin. If it happens to me as a= researcher it is<br> > >=C2=A0 =C2=A0 =C2=A0probably holding other people back as well. If= I could wave a magic<br> > >=C2=A0 =C2=A0 =C2=A0wand and turn on one of the disabled op codes = it would be OP_CAT. Of<br> > >=C2=A0 =C2=A0 =C2=A0course with the change that size of each conca= tenated value must be 64<br> > >=C2=A0 =C2=A0 =C2=A0Bytes or less.<br> ><br> > Why 64 bytes in particular?<br> ><br> > It seems obvious to me that this 64 bytes is most suited for building = Merkle trees, being the size of two SHA256 hashes.<br> ><br> > However we have had issues with the use of Merkle trees in Bitcoin blo= cks.<br> > Specifically, it is difficult to determine if a hash on a Merkle node = is the hash of a Merkle subnode, or a leaf transaction.<br> > My understanding is that this is the reason for now requiring transact= ions to be at least 80 bytes.<br> ><br> > The obvious fix would be to prepend the type of the hashed object, i.e= . add at least one byte to determine this type.<br> > Taproot for example uses tagged hash functions, with a different tag f= or leaves, and tagged hashes are just prepend-this-32-byte-constant-twice-b= efore-you-SHA256.<br> ><br> > This seems to indicate that to check merkle tree proofs, an `OP_CAT` w= ith only 64 bytes max output size would not be sufficient.<br> ><br> > Or we could implement tagged SHA256 as a new opcode...<br> ><br> > Regards,<br> > ZmnSCPxj<br> ><br> ><br> > ><br> > >=C2=A0 =C2=A0 =C2=A0On Tue, Oct 1, 2019 at 10:04 PM ZmnSCPxj via b= itcoin-dev<br> > >=C2=A0 =C2=A0 =C2=A0<a href=3D"mailto:bitcoin-dev@lists.linuxfound= ation.org" target=3D"_blank">bitcoin-dev@lists.linuxfoundation.org</a> wrot= e:<br> > ><br> > ><br> > > > Good morning lists,<br> > > > Let me propose the below radical idea:<br> > > ><br> > > > -=C2=A0 =C2=A0`SIGHASH` flags attached to signatures are a m= isdesign, sadly retained from the original BitCoin 0.1.0 Alpha for Windows = design, on par with:<br> > > >=C2=A0 =C2=A0 =C2=A0-=C2=A0 =C2=A01 RETURN<br> > > >=C2=A0 =C2=A0 =C2=A0-=C2=A0 =C2=A0higher-`nSequence` replacem= ent<br> > > >=C2=A0 =C2=A0 =C2=A0-=C2=A0 =C2=A0DER-encoded pubkeys<br> > > >=C2=A0 =C2=A0 =C2=A0-=C2=A0 =C2=A0unrestricted `scriptPubKey`= <br> > > >=C2=A0 =C2=A0 =C2=A0-=C2=A0 =C2=A0Payee-security-paid-by-paye= r (i.e. lack of P2SH)<br> > > >=C2=A0 =C2=A0 =C2=A0-=C2=A0 =C2=A0`OP_CAT` and `OP_MULT` and = `OP_ADD` and friends<br> > > >=C2=A0 =C2=A0 =C2=A0-=C2=A0 =C2=A0transaction malleability<br= > > > >=C2=A0 =C2=A0 =C2=A0-=C2=A0 =C2=A0probably many more<br> > > ><br> > > > So let me propose the more radical excision, starting with S= egWit v1:<br> > > ><br> > > > -=C2=A0 =C2=A0Remove `SIGHASH` from signatures.<br> > > > -=C2=A0 =C2=A0Put `SIGHASH` on public keys.<br> > > ><br> > > > Public keys are now encoded as either 33-bytes (implicit `SI= GHASH_ALL`) or 34-bytes (`SIGHASH` byte, followed by pubkey type, followed = by pubkey coordinate).<br> > > > `OP_CHECKSIG` and friends then look at the public key to det= ermine sighash algorithm rather than the signature.<br> > > > As we expect public keys to be indirectly committed to on ev= ery output `scriptPubKey`, this is automatically output tagging to allow pa= rticular `SIGHASH`.<br> > > > However, we can then utilize the many many ways to hide publ= ic keys away until they are needed, exemplified in MAST-inside-Taproot.<br> > > > I propose also the addition of the opcode:<br> > > ><br> > > >=C2=A0 =C2=A0 =C2=A0<sighash> <pubkey> OP_SETPUBK= EYSIGHASH<br> > > ><br> > > ><br> > > > -=C2=A0 =C2=A0`sighash` must be one byte.<br> > > > -=C2=A0 =C2=A0`pubkey` may be the special byte `0x1`, meanin= g "just use the Taproot internal pubkey".<br> > > > -=C2=A0 =C2=A0`pubkey` may be 33-byte public key, in which c= ase the `sighash` byte is just prepended to it.<br> > > > -=C2=A0 =C2=A0`pubkey` may be 34-byte public key with sighas= h, in which case the first byte is replaced with `sighash` byte.<br> > > > -=C2=A0 =C2=A0If `sighash` is `0x00` then the result is a 33= -byte public key (the sighash byte is removed) i.e. `SIGHASH_ALL` implicit.= <br> > > ><br> > > > This retains the old feature where the sighash is selected a= t time-of-spending rather than time-of-payment.<br> > > > This is done by using the script:<br> > > ><br> > > >=C2=A0 =C2=A0 =C2=A0<pubkey> OP_SETPUBKEYSIGHASH OP_CHE= CKSIG<br> > > ><br> > > ><br> > > > Then the sighash can be put in the witness stack after the s= ignature, letting the `SIGHASH` flag be selected at time-of-signing, but on= ly if the SCRIPT specifically is formed to do so.<br> > > > This is malleability-safe as the signature still commits to = the `SIGHASH` it was created for.<br> > > > However, by default, public keys will not have an attached `= SIGHASH` byte, implying `SIGHASH_ALL` (and disallowing-by-default non-`SIGH= ASH_ALL`).<br> > > > This removes the problems with `SIGHASH_NONE` `SIGHASH_SINGL= E`, as they are allowed only if the output specifically says they are allow= ed.<br> > > > Would this not be a superior solution?<br> > > > Regards,<br> > > > ZmnSCPxj<br> > > ><br> > > > bitcoin-dev mailing list<br> > > > <a href=3D"mailto:bitcoin-dev@lists.linuxfoundation.org" tar= get=3D"_blank">bitcoin-dev@lists.linuxfoundation.org</a><br> > > > <a href=3D"https://lists.linuxfoundation.org/mailman/listinf= o/bitcoin-dev" rel=3D"noreferrer" target=3D"_blank">https://lists.linuxfoun= dation.org/mailman/listinfo/bitcoin-dev</a><br> > ><br> > > Lightning-dev mailing list<br> > > <a href=3D"mailto:Lightning-dev@lists.linuxfoundation.org" target= =3D"_blank">Lightning-dev@lists.linuxfoundation.org</a><br> > > <a href=3D"https://lists.linuxfoundation.org/mailman/listinfo/lig= htning-dev" rel=3D"noreferrer" target=3D"_blank">https://lists.linuxfoundat= ion.org/mailman/listinfo/lightning-dev</a><br> ><br> ><br> _______________________________________________<br> Lightning-dev mailing list<br> <a href=3D"mailto:Lightning-dev@lists.linuxfoundation.org" target=3D"_blank= ">Lightning-dev@lists.linuxfoundation.org</a><br> <a href=3D"https://lists.linuxfoundation.org/mailman/listinfo/lightning-dev= " rel=3D"noreferrer" target=3D"_blank">https://lists.linuxfoundation.org/ma= ilman/listinfo/lightning-dev</a><br> </blockquote></div> --000000000000b73a1105940e9b4e--