Return-Path: Received: from smtp1.linuxfoundation.org (smtp1.linux-foundation.org [172.17.192.35]) by mail.linuxfoundation.org (Postfix) with ESMTPS id 050BD256 for ; Fri, 20 May 2016 11:34:13 +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 942561D1 for ; Fri, 20 May 2016 11:34:12 +0000 (UTC) Received: from neubau-gw.kalkbreite.net ([62.12.170.156]:32061 helo=[172.27.201.177]) by server47.web-hosting.com with esmtpsa (TLSv1:DHE-RSA-AES256-SHA:256) (Exim 4.86_1) (envelope-from ) id 1b3igz-000s12-MA; Fri, 20 May 2016 07:34:10 -0400 From: Johnson Lau Content-Type: multipart/alternative; boundary="Apple-Mail=_B8560957-882F-481C-8B0F-9AA06396F04D" Message-Id: Mime-Version: 1.0 (Mac OS X Mail 9.3 \(3124\)) Date: Fri, 20 May 2016 13:34:03 +0200 References: To: Matthew Roberts , bitcoin-dev In-Reply-To: X-Mailer: Apple Mail (2.3124) 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-Authenticated-Sender: server47.web-hosting.com: jl2012@xbt.hk X-Source: X-Source-Args: X-Source-Dir: X-From-Rewrite: unmodified, already matched X-Spam-Status: No, score=-1.9 required=5.0 tests=BAYES_00,HTML_MESSAGE, RCVD_IN_DNSWL_NONE autolearn=ham version=3.3.1 X-Spam-Checker-Version: SpamAssassin 3.3.1 (2010-03-16) on smtp1.linux-foundation.org Subject: Re: [bitcoin-dev] BIP: OP_PRANDOM 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: Fri, 20 May 2016 11:34:13 -0000 --Apple-Mail=_B8560957-882F-481C-8B0F-9AA06396F04D Content-Transfer-Encoding: quoted-printable Content-Type: text/plain; charset=us-ascii Using the hash of multiple blocks does not make it any safer. The miner = of the last block always determines the results, by knowing the hashes = of all previous blocks. >=20 > =3D=3D Security > Pay-to-script-hash can be used to protect the details of contracts = that use OP_PRANDOM from the prying eyes of miners. However, since there = is also a non-zero risk that a participant in a contract may attempt to = bribe a miner the inclusion of multiple block hashes as a source of = randomness is a must. Every miner would effectively need to be bribed to = ensure control over the results of the random numbers, which is already = very unlikely. The risk approaches zero as N goes up. --Apple-Mail=_B8560957-882F-481C-8B0F-9AA06396F04D Content-Transfer-Encoding: 7bit Content-Type: text/html; charset=us-ascii

Using the hash of multiple blocks does not make it any safer. The miner of the last block always determines the results, by knowing the hashes of all previous blocks.

== Security
Pay-to-script-hash can be used to protect the details of contracts that use OP_PRANDOM from the prying eyes of miners. However, since there is also a non-zero risk that a participant in a contract may attempt to bribe a miner the inclusion of multiple block hashes as a source of randomness is a must. Every miner would effectively need to be bribed to ensure control over the results of the random numbers, which is already very unlikely. The risk approaches zero as N goes up.

--Apple-Mail=_B8560957-882F-481C-8B0F-9AA06396F04D--