Return-Path: Received: from smtp1.linuxfoundation.org (smtp1.linux-foundation.org [172.17.192.35]) by mail.linuxfoundation.org (Postfix) with ESMTPS id 84210BD0 for ; Sun, 13 Dec 2015 15:25:13 +0000 (UTC) X-Greylist: from auto-whitelisted by SQLgrey-1.7.6 Received: from s47.web-hosting.com (s47.web-hosting.com [199.188.200.16]) by smtp1.linuxfoundation.org (Postfix) with ESMTPS id 77C06159 for ; Sun, 13 Dec 2015 15:25:12 +0000 (UTC) Received: from localhost ([::1]:39818 helo=server47.web-hosting.com) by server47.web-hosting.com with esmtpa (Exim 4.85) (envelope-from ) id 1a88WM-001lFt-SD; Sun, 13 Dec 2015 10:25:10 -0500 MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 8bit Date: Sun, 13 Dec 2015 10:25:10 -0500 From: jl2012@xbt.hk To: Gregory Maxwell In-Reply-To: References: Message-ID: <2498d6a0691fde6f62453294da6118d0@xbt.hk> X-Sender: jl2012@xbt.hk User-Agent: Roundcube Webmail/1.0.5 X-AntiAbuse: This header was added to track abuse, please include it with any abuse report X-AntiAbuse: Primary Hostname - server47.web-hosting.com X-AntiAbuse: Original Domain - lists.linuxfoundation.org X-AntiAbuse: Originator/Caller UID/GID - [47 12] / [47 12] X-AntiAbuse: Sender Address Domain - xbt.hk X-Get-Message-Sender-Via: server47.web-hosting.com: authenticated_id: jl2012@xbt.hk X-Source: X-Source-Args: X-Source-Dir: X-From-Rewrite: unmodified, already matched X-Spam-Status: No, score=-2.6 required=5.0 tests=BAYES_00,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 X-Mailman-Approved-At: Sun, 13 Dec 2015 17:13:13 +0000 Cc: Bitcoin Dev , gmaxwell@gmail.com Subject: Re: [bitcoin-dev] Segregated Witness features wish list X-BeenThere: bitcoin-dev@lists.linuxfoundation.org X-Mailman-Version: 2.1.12 Precedence: list List-Id: Bitcoin Development Discussion List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , X-List-Received-Date: Sun, 13 Dec 2015 15:25:13 -0000 -----BEGIN PGP SIGNED MESSAGE----- Hash: SHA256 I'm trying to list the minimal consensus rule changes needed for segwit softfork. The list does not cover the changes in non-consensus critical behaviors, such as relay of witness data. 1. OP_NOP4 is renamed as OP_SEGWIT 2. A script with OP_SEGWIT must fail if the scriptSig is not completely empty 3. If OP_SEGWIT is used in the scriptPubKey, it must be the only and the last OP code in the scriptPubKey, or the script must fail 4. The OP_SEGWIT must be preceded by exactly one data push (the "serialized script") with at least one byte, or the script must fail 5. The most significant byte of serialized script is the version byte, an unsigned number 6. If the version byte is 0x00, the script must fail 7. If the version byte is 0x02 to 0xff, the rest of the serialized script is ignored and the output is spendable with any form of witness (even if the witness contains something invalid in the current script system, e.g. OP_RETURN) 8. If the version byte is 0x01, 8a. rest of the serialized script is deserialized, and be interpreted as the scriptPubKey. 8b. the witness is interpreted as the scriptSig. 8c. the script runs with existing rules (including P2SH) 9. If the script fails when OP_SEGWIT is interpreted as a NOP, the script must fail. However, this is guaranteed by the rules 2, 3, 4, 6 so no additional check is needed. 10. The calculation of Merkle root in the block header remains unchanged 11. The witness commitment is placed somewhere in the block, either in coinbase or an OP_RETURN output in a specific tx Format of the witness commitment: The witness commitment could be as simple as a hash tree of all witness in a block. However, this is bad for further development of sum tree for compact SPV fraud proof as we have to maintain one more tree in the future. Even if we are not going to implement any sum checking in first version of segwit, it's better to make it easier for future softforks. (credit: gmaxwell) 12. The block should indicate how many sum criteria there are by committing the number following the witness commitment 13. The witness commitment is a hash-sum tree with the number of sum criteria committed in rule 12 14. Each sum criterion is a fixed 8 byte signed number (Negative value is allowed for use like counting delta-UTXO. 8 bytes is needed for fee commitment. Multiple smaller criteria may share a 8 byte slot, as long as they do not allow negative value) 15. Nodes will ignore the sum criteria that they do not understand, as long as the sum is correctly calculated Size limit: 16. We need to determine the size limit of witness 17. We also need to have an upper limit for the number of sum criteria, or a malicious miner may find a block with many unknown sum criteria and feed unlimited amount of garbage to other nodes. All other functions I mentioned in my wish list could be softforked later to this system To mitigate the risk described in rule 17, we may ask miners to vote for an increase (but not decrease) in the number of sum criteria. Initially there should be 0 sum criteria. If we would like to introduce a new criteria, miners will support the proposal by setting the number of sum criteria as 1. However, until 95% of miners support the increase, all values of the extra sum criteria must be 0. Therefore, even a malicious miner may declare any amount of sum criteria, those criteria unknown to the network must be 0, and no extra data is needed to construct the block. This voting mechanism could be a softfork over rule 12 and 13, and is not necessary in the initial segwit deployment. -----BEGIN PGP SIGNATURE----- Version: GnuPG v2 iQGcBAEBCAAGBQJWbY0jAAoJEO6eVSA0viTSU1oMAJIrYWerwk84poZBL/ezEsIp 9fCLnFZ4lyO2ijAm5UmwLXGijY03kqp29b0zmyIWV2WuoeW2lN64tLHQRilT0+5R n5/viQOMv0C0MYs525+/dpNkk2q2MiFmyyozdbU6zcyfdkrkYdChCFOQ9GsxzQHk n4lL4/RSKdqJZg4x2yEGgdyKA6XrQHaFirdr/K2bhhbk4Q0SOuYjy8Wxa2oCHFCC WG4K2NBnKCI7DuVXQK+ZC8dYXMwbemeFfPHY6dZVti7j/OFsllyxno/CFKO3rsCs +uko4XJk6pH0Ncjrc1n0l0v9xIKF5hTqSxFs+GVvhkiBdTDZVe7CdedO9qJWf1hE bbmLXTURCDQUFe9F3uKsnYfMoD5eniWHx2OQcJcNPlLMJd9zObB3HdgFMW6N53KN QXLmxobU/xFhmFknz1ShGEIdGSaH0gqnb+WEkO5v5vBO4L6Cikc+lcp7zXqQzWpW uqm3QSrbKcbR6JEwDFoGQpDkcqpwpTIrOAk4B1jJRg== =J2KF -----END PGP SIGNATURE----- Gregory Maxwell 於 2015-12-10 04:51 寫到: > On Thu, Dec 10, 2015 at 6:47 AM, jl2012--- via bitcoin-dev > wrote: >> 4. Sum of fee, sigopcount, size etc as part of the witness hash tree: >> for > > I should have also commented on this: the block can indicate how many > sum criteria there are; and then additional ones could be soft-forked > in. Haven't tried implementing it yet, but there you go. :)