Received: from sog-mx-1.v43.ch3.sourceforge.com ([172.29.43.191] helo=mx.sourceforge.net) by sfs-ml-3.v29.ch3.sourceforge.com with esmtp (Exim 4.76) (envelope-from ) id 1Xa5YN-0002p8-GU for bitcoin-development@lists.sourceforge.net; Fri, 03 Oct 2014 16:17:59 +0000 Received-SPF: pass (sog-mx-1.v43.ch3.sourceforge.com: domain of gmail.com designates 209.85.213.173 as permitted sender) client-ip=209.85.213.173; envelope-from=gmaxwell@gmail.com; helo=mail-ig0-f173.google.com; Received: from mail-ig0-f173.google.com ([209.85.213.173]) by sog-mx-1.v43.ch3.sourceforge.com with esmtps (TLSv1:RC4-SHA:128) (Exim 4.76) id 1Xa5YM-0005DR-Ll for bitcoin-development@lists.sourceforge.net; Fri, 03 Oct 2014 16:17:59 +0000 Received: by mail-ig0-f173.google.com with SMTP id h18so268887igc.6 for ; Fri, 03 Oct 2014 09:17:49 -0700 (PDT) MIME-Version: 1.0 X-Received: by 10.50.28.13 with SMTP id x13mr15780831igg.8.1412353068875; Fri, 03 Oct 2014 09:17:48 -0700 (PDT) Received: by 10.107.168.5 with HTTP; Fri, 3 Oct 2014 09:17:48 -0700 (PDT) In-Reply-To: <1987325.zKPNeYyO8K@crushinator> References: <20141001130826.GM28710@savin.petertodd.org> <1987325.zKPNeYyO8K@crushinator> Date: Fri, 3 Oct 2014 09:17:48 -0700 Message-ID: From: Gregory Maxwell To: Matt Whitlock Content-Type: text/plain; charset=UTF-8 X-Spam-Score: -1.6 (-) X-Spam-Report: Spam Filtering performed by mx.sourceforge.net. See http://spamassassin.org/tag/ for more details. -1.5 SPF_CHECK_PASS SPF reports sender host as permitted sender for sender-domain 0.0 FREEMAIL_FROM Sender email is commonly abused enduser mail provider (gmaxwell[at]gmail.com) -0.0 SPF_PASS SPF: sender matches SPF record -0.1 DKIM_VALID_AU Message has a valid DKIM or DK signature from author's domain 0.1 DKIM_SIGNED Message has a DKIM or DK signature, not necessarily valid -0.1 DKIM_VALID Message has at least one valid DKIM or DK signature X-Headers-End: 1Xa5YM-0005DR-Ll Cc: Bitcoin Development , Flavien Charlon Subject: Re: [Bitcoin-development] [BIP draft] CHECKLOCKTIMEVERIFY - Prevent a txout from being spent until an expiration time X-BeenThere: bitcoin-development@lists.sourceforge.net X-Mailman-Version: 2.1.9 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , X-List-Received-Date: Fri, 03 Oct 2014 16:17:59 -0000 On Fri, Oct 3, 2014 at 7:28 AM, Matt Whitlock wrote: > Is there a reason why we can't have the new opcode simply replace the top stack item with the block height of the txout being redeemed? This would not be soft-forking compatible. It also would be unsafe in that it would result in transactions which once mined could not be restored in a reorg through no fault of the participants, which makes the coins less fungible and differently safe to accept. It risks creating weird pressures around immediate block admission since a one additional block delay could forever censor such a transaction (E.g. increases the power of single miners to censor or steal). Avoiding this is a conscious decision in Bitcoin and also part of the justification for the 100 block maturity of newly generated coins. It also would require violating the script/transaction/block layering more substantially, complicating implementations, and making the validity of a script no longer a deterministic pure function of the transaction. Avoiding these issues is a conscious design in OP_CHECKLOCKTIMEVERIFY. I would strenuously oppose a proposal which failed in any of these respects. > Then arbitrary logic could be implemented, including "output cannot be spent until a certain time" and also "output can ONLY be spent until a certain time," as well as complex logic with alternative key groups with differing time constraints. You can already achieve the not spendable after logic with a cancellation spend that moves the coin in the usual way. (Which doesn't even require the participant be online, with the help of some network service to queue unlocked transactions). > OP_CHECKLOCKTIMEVERIFY, as conceived, seems too limited, IMHO. It is intentionally so, and yet it covers the intended use cases; including ones with alternative key groups, they are just not exclusive.