Return-Path: Received: from smtp1.linuxfoundation.org (smtp1.linux-foundation.org [172.17.192.35]) by mail.linuxfoundation.org (Postfix) with ESMTPS id 40DCE2818 for ; Wed, 2 Oct 2019 02:03:53 +0000 (UTC) X-Greylist: domain auto-whitelisted by SQLgrey-1.7.6 Received: from mail-40135.protonmail.ch (mail-40135.protonmail.ch [185.70.40.135]) by smtp1.linuxfoundation.org (Postfix) with ESMTPS id 8E202189 for ; Wed, 2 Oct 2019 02:03:52 +0000 (UTC) Date: Wed, 02 Oct 2019 02:03:43 +0000 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=protonmail.com; s=default; t=1569981830; bh=8PdzcP4EQtz7VSC2reC2pAg5xm/hEszQeeIlWJlEb4I=; h=Date:To:From:Cc:Reply-To:Subject:In-Reply-To:References: Feedback-ID:From; b=d9yT5iZ3s8+eblGWitSPWIWf6mIA3tSANQ4kMNR18AuuIknoe/XvWW6ClnEthDgVV 14y47DbudGKetAieU/hwsn1SpCzcUdSUCbJukkULu/ZhFTrJX6fA/XbOCRJW2geTE0 TcbBggkWGia9//cv7W7mDS9wW7RS0uFPXQD/jI7o= To: Bitcoin Protocol Discussion From: ZmnSCPxj Reply-To: ZmnSCPxj Message-ID: In-Reply-To: <20191001155929.e2yznsetqesx2jxo@erisian.com.au> References: <87wodp7w9f.fsf@gmail.com> <20191001155929.e2yznsetqesx2jxo@erisian.com.au> Feedback-ID: el4j0RWPRERue64lIQeq9Y2FP-mdB86tFqjmrJyEPR9VAtMovPEo9tvgA0CrTsSHJeeyPXqnoAu6DN-R04uJUg==:Ext:ProtonMail MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: quoted-printable X-Spam-Status: No, score=-2.2 required=5.0 tests=BAYES_00,DKIM_SIGNED, DKIM_VALID, DKIM_VALID_AU, DOS_RCVD_IP_TWICE_B, FREEMAIL_FROM, FROM_LOCAL_NOVOWEL, RCVD_IN_DNSWL_LOW autolearn=ham version=3.3.1 X-Spam-Checker-Version: SpamAssassin 3.3.1 (2010-03-16) on smtp1.linux-foundation.org Cc: "lightning-dev@lists.linuxfoundation.org" Subject: Re: [bitcoin-dev] 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 List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , X-List-Received-Date: Wed, 02 Oct 2019 02:03:53 -0000 Good morning lists, Let me propose the below radical idea: * `SIGHASH` flags attached to signatures are a misdesign, sadly retained fr= om 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 coord= inate). `OP_CHECKSIG` and friends then look at the *public key* to determine sighas= h algorithm rather than the signature. As we expect public keys to be indirectly committed to on every output `scr= iptPubKey`, this is automatically output tagging to allow particular `SIGHA= SH`. However, we can then utilize the many many ways to hide public keys away un= til they are needed, exemplified in MAST-inside-Taproot. I propose also the addition of the opcode: OP_SETPUBKEYSIGHASH * `sighash` must be one byte. * `pubkey` may be the special byte `0x1`, meaning "just use the Taproot int= ernal pubkey". * `pubkey` may be 33-byte public key, in which case the `sighash` byte is j= ust 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 sigha= sh byte is removed) i.e. `SIGHASH_ALL` implicit. This retains the old feature where the sighash is selected at time-of-spend= ing rather than time-of-payment. This is done by using the script: OP_SETPUBKEYSIGHASH OP_CHECKSIG Then the sighash can be put in the witness stack after the signature, letti= ng the `SIGHASH` flag be selected at time-of-signing, but only if the SCRIP= T specifically is formed to do so. This is malleability-safe as the signature still commits to the `SIGHASH` i= t 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