From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from smtp1.linuxfoundation.org (smtp1.linux-foundation.org [172.17.192.35]) by mail.linuxfoundation.org (Postfix) with ESMTPS id 8723FFBE for ; Fri, 12 Feb 2016 11:31:57 +0000 (UTC) X-Greylist: whitelisted by SQLgrey-1.7.6 Received: from mail-ob0-f169.google.com (mail-ob0-f169.google.com [209.85.214.169]) by smtp1.linuxfoundation.org (Postfix) with ESMTPS id BD728D2 for ; Fri, 12 Feb 2016 11:31:56 +0000 (UTC) Received: by mail-ob0-f169.google.com with SMTP id gc3so15943781obb.3 for ; Fri, 12 Feb 2016 03:31:56 -0800 (PST) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=glados-cc.20150623.gappssmtp.com; s=20150623; h=mime-version:sender:in-reply-to:references:date:message-id:subject :from:to:content-type; bh=jCfeFMnaJ7L5gm8Jku80GfKAehnXH4LsGAeB5a+bz7o=; b=rQJk8QINqtI5zShsLukADU+8/4PlatSeS3tdPdJ5A3FsZDIcUVT1t0NGvEDH3kFm4h Ih/B0PugZLTlatGBGkFiU8m/s4txXLhbu5BXS2ehMeUpxWRSCGFL30qmZbCwxgZe8juz V8eFKyJ31N9BXKrw5k2NAL4j1PZsifIkttKRonqYa6ImBJZ1ggm1DKtlmbUVlKSIH8O0 78fk93WqAMHJyKjMuZjbiGqdZXDGpaWp+TBtyl/4glOm5z3i6C7D700E9vYpLyKInOyn DIJ9O9HgpRmWTxumCGCtQfbWbQufcezxj0J9CPEtF8oR++4XHv97toQep0ovjh3KkZ0C uyrg== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20130820; h=x-gm-message-state:mime-version:sender:in-reply-to:references:date :message-id:subject:from:to:content-type; bh=jCfeFMnaJ7L5gm8Jku80GfKAehnXH4LsGAeB5a+bz7o=; b=Ta/gGcnsj5KOC6/REnHjdiZB/6WtvrY4UuOsFUmtC67jfY5seZp1zJyHcLieWL4fbo P6BUhkNFxCX+j9hyjewqi2pYkQAHvkwaS1oRxxFnk1tgMZ2b+jN4cFl6XRm6jWtxozgl SufB7SKd4C+1EByhyf2NF5Y9/LxMZrqVEpcdbqh5c1XGyuL/K+/mJ7rIqaaSMukAXM/H +m1Ikje+z/oGnfJ/CMUATzQO60hOen6DaHvx2VkP50+vFQL7CAKqBkebq4O7E0Ezjvn2 bkUiwwxx/YbPd5b6x/r0eo9ATn3jic2gfmOByTavBiB3dcmJmMEeBAbpalXm0CcZy5E/ WZvw== X-Gm-Message-State: AG10YOQQDDlKPwboFMFj5FvEIvbAIZlZOp0du9KUyfPCL+IIMfLmsTef1MiFnlVti8yPj+3AEdJkbepJcQmkng== MIME-Version: 1.0 X-Received: by 10.202.77.11 with SMTP id a11mr697378oib.23.1455276716124; Fri, 12 Feb 2016 03:31:56 -0800 (PST) Sender: admin@glados.cc Received: by 10.202.214.2 with HTTP; Fri, 12 Feb 2016 03:31:56 -0800 (PST) X-Originating-IP: [49.182.145.219] Received: by 10.202.214.2 with HTTP; Fri, 12 Feb 2016 03:31:56 -0800 (PST) In-Reply-To: References: Date: Fri, 12 Feb 2016 22:31:56 +1100 X-Google-Sender-Auth: HLKujp5AgTyeoo7pMn-mulSyPjE Message-ID: From: gladoscc To: Bitcoin Dev Content-Type: multipart/alternative; boundary=001a11494d0eb70853052b910339 X-Spam-Status: No, score=-2.6 required=5.0 tests=BAYES_00,DKIM_SIGNED, DKIM_VALID,HTML_MESSAGE,RCVD_IN_DNSWL_LOW autolearn=ham version=3.3.1 X-Spam-Checker-Version: SpamAssassin 3.3.1 (2010-03-16) on smtp1.linux-foundation.org X-Mailman-Approved-At: Fri, 12 Feb 2016 15:16:43 +0000 Subject: [bitcoin-dev] Soft fork fix for block withholding attacks X-BeenThere: bitcoin-dev@lists.linuxfoundation.org X-Mailman-Version: 2.1.12 Precedence: list List-Id: Bitcoin Development Discussion List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , X-List-Received-Date: Fri, 12 Feb 2016 11:31:57 -0000 --001a11494d0eb70853052b910339 Content-Type: text/plain; charset=UTF-8 Here's a method of fixing block withholding attacks with a soft fork: We require blocks to choose an arbitrary target, e.g. two bytes. We redefine the block PoW target to be "less than the difficulty, with the last two bytes being the target". We require blocks to include a blinded hash of the target plus some junk (which blinds it) in the coinbase. The miner cannot arbitrarily switch targets. The miner can now send the block header to hashers. Hashers do not know the target, and hence must submit all shares that matches the first PoW criteria (below difficulty) and delegate secondary verification to the miner. With two bytes as the target, there are 65335 false positives for every valid block. Finally, we require miners to communicate a proof of their target hash (ie, the junk they generated) in a non-hashed area of the block. This can be a protocol extension. The target is already included in the hash as the last two bytes. This can be deployed as a soft fork with miner opt in, triggering across many difficulty cycles. Initially, we soft fork to require the last bit of the block hash to be zero. The next difficulty cycle, we require the last two bits to be zero. We do this 16 times to get 2 bytes, and then we actually activate targets. By then, nominal difficulty would have been cut by 2^16 (65536), but the block target makes mining each block 65536 times as hard. We do the progression over 16 difficulty cycles to minimise increases in block timings. We can be more specific and progress over even more difficulty cycles through more clever soft fork rules. For example, Vitalik detailed "timewalking" attacks that allow effective granular lowering of the nominal difficulty. Critique welcome. --001a11494d0eb70853052b910339 Content-Type: text/html; charset=UTF-8 Content-Transfer-Encoding: quoted-printable

Here's a method of fixing block withholding attacks with= a soft fork:

We require blocks to choose an arbitrary target, e.g. two by= tes. We redefine the block PoW target to be "less than the difficulty,= with the last two bytes being the target".

We require blocks to include a blinded hash of the target pl= us some junk (which blinds it) in the coinbase. The miner cannot arbitraril= y switch targets.

The miner can now send the block header to hashers. Hashers = do not know the target, and hence must submit all shares that matches the f= irst PoW criteria (below difficulty) and delegate secondary verification to= the miner. With two bytes as the target, there are 65335 false positives f= or every valid block.

Finally, we require miners to communicate a proof of their t= arget hash (ie, the junk they generated) in a non-hashed area of the block.= This can be a protocol extension. The target is already included in the ha= sh as the last two bytes.

This can be deployed as a soft fork with miner opt in, trigg= ering across many difficulty cycles. Initially, we soft fork to require the= last bit of the block hash to be zero. The next difficulty cycle, we requi= re the last two bits to be zero. We do this 16 times to get 2 bytes, and th= en we actually activate targets.

By then, nominal difficulty would have been cut by 2^16 (655= 36), but the block target makes mining each block 65536 times as hard. We d= o the progression over 16 difficulty cycles to minimise increases in block = timings. We can be more specific and progress over even more difficulty cyc= les through more clever soft fork rules.

For example, Vitalik detailed "timewalking" attack= s that allow effective granular lowering of the nominal difficulty.

Critique welcome.

--001a11494d0eb70853052b910339--