From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from sog-mx-1.v43.ch3.sourceforge.com ([172.29.43.191] helo=mx.sourceforge.net) by sfs-ml-1.v29.ch3.sourceforge.com with esmtp (Exim 4.76) (envelope-from ) id 1RgAJE-0003PD-2f for bitcoin-development@lists.sourceforge.net; Thu, 29 Dec 2011 07:21:52 +0000 X-ACL-Warn: Received: from erdos.theorem.ca ([72.2.4.176] helo=theorem.ca) by sog-mx-1.v43.ch3.sourceforge.com with smtp (Exim 4.76) id 1RgAJC-0006e1-MF for bitcoin-development@lists.sourceforge.net; Thu, 29 Dec 2011 07:21:52 +0000 Received: (qmail 2362 invoked by uid 603); 29 Dec 2011 06:55:03 -0000 Received: from localhost (sendmail-bs@127.0.0.1) by localhost with SMTP; 29 Dec 2011 06:55:03 -0000 Date: Thu, 29 Dec 2011 01:55:03 -0500 (EST) From: roconnor@theorem.ca To: bitcoin-development@lists.sourceforge.net Message-ID: User-Agent: Alpine 2.00 (LRH 1167 2008-08-23) MIME-Version: 1.0 Content-Type: TEXT/PLAIN; format=flowed; charset=US-ASCII X-Spam-Score: -1.9 (-) X-Spam-Report: Spam Filtering performed by mx.sourceforge.net. See http://spamassassin.org/tag/ for more details. -1.3 RP_MATCHES_RCVD Envelope sender domain matches handover relay domain -0.7 AWL AWL: From: address is in the auto white-list X-Headers-End: 1RgAJC-0006e1-MF Cc: webmaster@btcguild.com, pool@deepbit.net Subject: [Bitcoin-development] Alternative to OP_EVAL 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: Thu, 29 Dec 2011 07:21:52 -0000 Gavin asked me to come up with an alternative to OP_EVAL, so here is my proposal. OP_CODEHASH Initial Proposal The idea is to add third "codehash" stack to the scripting engine (or alternatively a codehash state variable) and have OP_CODESEPARATOR in addition to its current behaviour push the hash of the remaining code in the script onto the codehash stack (or alternatively set the codehash state variable). Then we add a new OP_CODEHASH operator that pops the codehash stack and pushes it onto the main stack (or alternatively push the value of the codehash state variable onto the mainstack which is initialized using the hash of the sigScript). The new send-to-script transaction would be: OP_CODEHASH OP_HASH160 {20-byte-hash-value} OP_EQUAL Which can be redeemed by {20-byte-code-hash} signatures OP_CODESEPARATOR code When run the code will consume all the signatures leaving the 20-byte-code-hash on the stack. When OP_CODEHASH is interpreted as a NOP it is skipped, then the hash is hashed and compared to the 20-byte-hash-value and a match is required to succeed. When OP_CODEHASH is interpreted by a new client it pops the codehash stack and pushes the value onto the main stack, which in this standard transaction pushes a value identical to the existing {20-byte-code-hash} on the stack. Then again this hash is hashed and compared to to {20-byte-code-hash}. This proposal covers all the desired behaviour from OP_EVAL proposal but with a less radical change: (1) you get send-to-script addresses (2) you cannot redeem with the old client without knowing the hash of the script OP_CODEHASH has no dynamically generated code that is executed. The language remains a weak stack based language which is clearly terminating. The number of operations executed is still bounded by the number of operations occurring in the script. With the OP_EVAL proposal the script language becomes essentially Turing complete, with only an artificial limit on recursion depth preventing arbitrary computation and there is no way to know what code will run without executing it. With the OP_EVAL proposal there is no way to statically analyze the script (say to count the number of uses of OP_CHECKSIG or OP_MULTICHECKSIG or other analysis) without actually executing the script. This is just an initial proposal there are clearly some variations that could be done that would work just as well. Thanks goes to luke-jr and others for their thoughts on this proposal. Good night everyone. -- Russell O'Connor ``All talk about `theft,''' the general counsel of the American Graphophone Company wrote, ``is the merest claptrap, for there exists no property in ideas musical, literary or artistic, except as defined by statute.''