From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from sog-mx-3.v43.ch3.sourceforge.com ([172.29.43.193] helo=mx.sourceforge.net) by sfs-ml-2.v29.ch3.sourceforge.com with esmtp (Exim 4.76) (envelope-from ) id 1UFOuw-0003Rw-0D for bitcoin-development@lists.sourceforge.net; Tue, 12 Mar 2013 13:06:58 +0000 Received-SPF: pass (sog-mx-3.v43.ch3.sourceforge.com: domain of gmail.com designates 209.85.215.44 as permitted sender) client-ip=209.85.215.44; envelope-from=gmaxwell@gmail.com; helo=mail-la0-f44.google.com; Received: from mail-la0-f44.google.com ([209.85.215.44]) by sog-mx-3.v43.ch3.sourceforge.com with esmtps (TLSv1:RC4-SHA:128) (Exim 4.76) id 1UFOut-0008Tm-UX for bitcoin-development@lists.sourceforge.net; Tue, 12 Mar 2013 13:06:57 +0000 Received: by mail-la0-f44.google.com with SMTP id eb20so5180258lab.3 for ; Tue, 12 Mar 2013 06:06:49 -0700 (PDT) MIME-Version: 1.0 X-Received: by 10.112.26.202 with SMTP id n10mr6237747lbg.15.1363093609157; Tue, 12 Mar 2013 06:06:49 -0700 (PDT) Received: by 10.112.96.164 with HTTP; Tue, 12 Mar 2013 06:06:49 -0700 (PDT) In-Reply-To: <20130312094700.GA8130@savin> References: <20130312094700.GA8130@savin> Date: Tue, 12 Mar 2013 06:06:49 -0700 Message-ID: From: Gregory Maxwell To: Peter Todd 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: 1UFOut-0008Tm-UX Cc: Bitcoin Dev Subject: Re: [Bitcoin-development] Changing the fee on already sent transactions 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: Tue, 12 Mar 2013 13:06:58 -0000 On Tue, Mar 12, 2013 at 2:47 AM, Peter Todd wrote: > Followed by the actual replacement logic. We could change this logic to > instead evaluate if the candidate replacement does not remove or > decrease the value of any existing outputs. Adding outputs is ok. > Changing the set of inputs is also ok, provided that there are no > conflicts with other spent transactions. DoS attacks would be prevented > by only forwarding/accepting into the mempool replacements that increase > the fees paid by at least MIN_RELAY_TX_FEE * size - essentially the same > decision to allow the broadcast of the transaction in the first place. I _strongly_ prefer this method of addressing this concern. I think you've hit the required requirements: pay at least all the same inputs, increase fee by at least the min_relay_tx_fee*size. The discussion we had on IRC where some were proposing fast expiration would practically lower the security of Bitcoin. While there is complexity and testing required here, getting full branch coverage of this code would be fairly straight forward. Doing this correctly will be easier than child-pays-for-parent and although it does not replace child-pays-for-parent (the two techniques are complimentary in my view) it would reduce the urgency of getting child-pays-for-parent included.