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[67.82.16.19]) by mx.google.com with ESMTPSA id 6sm26974773qam.44.2014.06.03.07.43.40 for (version=TLSv1 cipher=ECDHE-RSA-RC4-SHA bits=128/128); Tue, 03 Jun 2014 07:43:41 -0700 (PDT) Message-ID: <538DDF1B.30701@gmail.com> Date: Tue, 03 Jun 2014 10:43:39 -0400 From: Kevin User-Agent: Mozilla/5.0 (Windows NT 6.1; WOW64; rv:24.0) Gecko/20100101 Thunderbird/24.5.0 MIME-Version: 1.0 To: bitcoin-development@lists.sourceforge.net References: <2341954.NpNStk60qp@1337h4x0r> In-Reply-To: <2341954.NpNStk60qp@1337h4x0r> Content-Type: text/plain; charset=ISO-8859-1; format=flowed Content-Transfer-Encoding: 7bit X-Spam-Score: -1.4 (-) 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 (kevinsisco61784[at]gmail.com) -0.0 SPF_PASS SPF: sender matches SPF record 0.2 FREEMAIL_ENVFROM_END_DIGIT Envelope-from freemail username ends in digit (kevinsisco61784[at]gmail.com) -0.0 RCVD_IN_DNSWL_NONE RBL: Sender listed at http://www.dnswl.org/, no trust [209.85.192.52 listed in list.dnswl.org] -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: 1WrpwJ-00085C-Vp Subject: Re: [Bitcoin-development] Lets discuss what to do if SHA256d is actually broken 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, 03 Jun 2014 14:43:49 -0000 On 6/3/2014 12:29 AM, xor wrote: > -----BEGIN PGP SIGNED MESSAGE----- > Hash: SHA256 > > Hi, > > I thought a lot about the worst case scenario of SHA256d being broken in a way > which could be abused to > A) reduce the work of mining a block by some significant amount > B) reduce the work of mining a block to zero, i.e. allow instant mining. > > Bitcoin needs to be prepared for this as any hash function has a limited > lifetime. Usually crypto stuff is not completely broken instantly by new > attacks but gradually. For example first the attack difficulty is reduced from > 2^128 to 2^100, then 2^64, etc. > This would make scenario A more likely. > > Now while B sounds more dangerous, I think in fact A is: > Consider how A would happen in real life: Someone publishes a paper of a > theoretical reduction of SHA256d attacks to 2^96 bit. Mathematicians will > consider this as a serious attack and create a lot of riot. > If no plan is made early enough, as in now, the Bitcoin Core team might then > probably want to just do the easiest approach of replacing the hash function > after a certain block number, i.e. a hard fork. > But what about the Bitcoin miners, those who need to actually accept a change > of mining algorithm which renders their hardware which cost MILLIONS > completely worthless? > Over the years they have gotten used to exponential growth of the Bitcoin > networks hashrate, and therefore exponential devaluation of their mining > hardware. Even if the attack on SHA256d causes a significant growth of > difficulty, the miners will not *believe* that it is an actual attack on SHA256d > - - maybe it is just some new large mining operation? They are used to this > happening! Why should they believe this and switch to a new hash function > which requires completely new hardware and therefore costs them millions? > They will just keep mining SHA256d. Thats why this is more dangerous, because > changing the hash funciton won't be accepted by the miners even though it is > broken. > Something smarter needs to be thought of. > > Now I must admit that I am not good at cryptography at all, but I had the > following idea: Use the altcoin concept of having multiple hash functions in a > chain. If SHA256d is broken, it is chained with a new hash function. > Thereby, people who want to mine the new replacement hash function still will > need ASICs which can solve the old SHA proof of work. So existing ASIC owners > can amend their code to do SHA256d using the ASIC, and then the second hash > function using a general purpose CPU. > This would also allow a smooth migration of difficulty - I don't even know how > difficulty would react with the naive approach of just replacing SHA with > something else: It would probably be an unsolvable problem to define new rules > to make it decrease enough so new blocks can actually be mined by the now > several orders of magnitude slower CPU-only mining community but still be high > enough to be able to deal with the fact that millions of people will try their > luck with mining at the release date. > > While this sounds simple in theory, it might be a lot of work to implement, so > you guys might want to take precautions for it soon :) > > Greetings, > xor - A Freenet project developer > > -----BEGIN PGP SIGNATURE----- > Version: GnuPG v1.4.14 (GNU/Linux) > > iQIcBAEBCAAGBQJTjU9DAAoJEMtmZ+8tjWt5pNEP/2460eHu7ujrUSxinJXY7+wF > E759/NcpNuakqu4NsS3ndi8lSiVIeixiOWZxPwLYkzC0pgPd5JrK5hdrYewsgreL > Ltkh6LKB4YZLYrV3jm62ZPMTzCopYQ1l872xbN3PJQJoXhEp4fKu99++LDzVg9Gk > n7rvrk6Iy/nSsZ1IMANpKghbU8/Gtn6ppCJv9rxRE//CZdTso1tTyOXXkEEMTHcV > y/iv6CHXtTXPvOgEgciU0oCPq0NOUKdIAOD//ybcKzncOoHSmwr1rZdreCTH6/Ek > 9uwq/HaQnseHPrq9qrIkIKrZDlnjKu7Tqw1BlbyBeCrWdJPCeDJg2kyCXgTvIzFD > oXwZ6r16tb2QPR4ByyO1lZy9G2Pp26thk12BnadnPYTf1rMvsY15BjfUrCU9ppt/ > YpFAZSFlXUGOuOBKUznUeO8U1bXJylcTTnyER/cudOpcKR8Jt9l5tfm5LTHCB6Q2 > Tjmvsmd0BzwafLEhHD5FHoTZFNVdXWvEUO/w4I/2UWTS7CacbE1qk0rVpsF/4L1K > /oFVnZIUKqsm5mMMb6WTQq+MjP2TF/eAAwm2UtFYmj0FVML9HBNwyiAc5UKwnD4Y > Yq3Pl5QfRobwu6pgT3zO7vK+saOl8sePWbU8Skj41OTEDrJM4QIQGAqs1U8xke8+ > YnUYiyzreJ8ofHhNBs4/ > =dkuk > -----END PGP SIGNATURE----- > > > ------------------------------------------------------------------------------ > Learn Graph Databases - Download FREE O'Reilly Book > "Graph Databases" is the definitive new guide to graph databases and their > applications. Written by three acclaimed leaders in the field, > this first edition is now available. Download your free book today! > http://p.sf.net/sfu/NeoTech > _______________________________________________ > Bitcoin-development mailing list > Bitcoin-development@lists.sourceforge.net > https://lists.sourceforge.net/lists/listinfo/bitcoin-development It is good to start thinking about such things. Let's face it, it could happen. However, short of having bitcoin use another algorithm for encryption, I am not sure much could be done. That's just me. -- Kevin