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120 lines
5.2 KiB
HTML
120 lines
5.2 KiB
HTML
---
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title: "Some Miners Generating Invalid Blocks"
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alias: "spv-mining"
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active: true
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banner: "WARNING: many wallets currently vulnerable to double-spending of confirmed transactions (click here to read)"
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bannerclass: "alert"
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---
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<p><em>This document is being updated as new information arrives. Last
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update: 2015-07-04 16:00 UTC</em></p>
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{% assign confs="30" %}
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<h2 id="summary">Summary</h2>
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<p>Your bitcoins are safe if you received them in transactions confirmed before 2015-07-04 15:00 UTC.</p>
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<p>However, there has been a problem with a planned upgrade. For
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bitcoins received later than the time above, confirmation scores are
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significantly less reliable then they usually are for users of
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certain software:</p>
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<ul>
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<li><b>Lightweight (<a href="http://bitcoin.stackexchange.com/questions/4649/what-is-an-spv-client">SPV</a>) wallet users</b> should wait an additional {{confs}}
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confirmations more than you would normally wait.</li>
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<li><b>Bitcoin Core 0.9.4 or earlier users</b> should wait an
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additional {{confs}} confirmations more than you would normally
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wait or upgrade to <a href="/en/download">Bitcoin Core 0.10.2</a>.</li>
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<li><b>Web wallet users</b> should wait an additional {{confs}} confirmations
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more than you would normally wait, unless you know for sure that your
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wallet is secured by Bitcoin Core 0.9.5 or later.</li>
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<li><b>Bitcoin Core 0.9.5 or later users are unaffected.</b> (Note:
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<a href="/en/download">upgrade to 0.10.2</a> is recommended due to
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denial-of-service vulnerabilities unrelated to this alert.)</li>
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</ul>
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<h2 id="miners">Miners</h2>
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<p>If you pool mine, please switch to a pool that properly validates
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blocks. The Wiki Mining Pool Comparison page currently contains a list of <a
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href="https://en.bitcoin.it/wiki/Comparison_of_mining_pools#SPV_Mining_.2F_Old_Bitcoin_Core">known (or
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suspected) good and bad pools.</a></p>
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<p>If you solo mine, please switch to Bitcoin Core 0.10.2.</p>
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<h2 id="solution">When Will Things Go Back To Normal?</h2>
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<p>The problem is miners creating invalid blocks. Some software can detect
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that those blocks are invalid and reject them; other software can't
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detect that blocks are invalid, so they show confirmations that aren't
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real.</p>
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<ul>
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<li><b>Bitcoin Core 0.9.5 and later</b> never had any problems because
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it could detect which blocks were invalid.</li>
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<li><b>Bitcoin Core 0.9.4 and earlier</b> will never provide as much
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security as later versions of Bitcoin Core because it doesn't know
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about the additional <a
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href="https://github.com/bitcoin/bips/blob/master/bip-0066.mediawiki">BIP66</a>
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consensus rules. <a href="/en/download">Upgrade</a> is recommended
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to return to full node security.</li>
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<li><b>Lightweight (SPV) wallets</b> are not safe for less than
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{{confs}} confirmations until all the major pools switch to full
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validation.</li>
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<li><b>Web wallets</b> are very diverse in what infrastructure they
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run and how they handle double spends, so unless you know for sure
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that they use Bitcoin Core 0.9.5 or later for full validation, you
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should assume they have the same security as the lightweight
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wallets described above.</li>
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</ul>
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<h2 id="cause">What's Happening</h2>
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<p>Summary: Some miners are currently generating invalid blocks. Almost
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all software (besides Bitcoin Core 0.9.5 and later) will accept these
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invalid blocks under certain conditions. The paragraphs that follow
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explain the cause more throughly.</p>
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<p>For several months, an increasing amount of mining hash rate has been
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signaling its intent to begin enforcing <a
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href="https://github.com/bitcoin/bips/blob/master/bip-0066.mediawiki">BIP66</a>
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strict DER signatures. As part of the BIP66 rules,
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once 950 of the last 1,000 blocks were version 3 (v3) blocks, all
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upgraded miners would reject version 2 (v2) blocks.</p>
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<p>Early morning UTC on 4 July 2015, the 950/1000 (95%) threshold was
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reached. Shortly thereafter, a small miner (part of the non-upgraded
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5%) mined an invalid block--as was an expected occurrence.
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Unfortunately, it turned out that roughly half the network hash rate
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was mining without fully validating blocks (called SPV mining), and
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built new blocks on top of that invalid block.</p>
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<p>Note that the roughly 50% of the network that was SPV mining had
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explicitly indicated that they would enforce the BIP66 rules. By not
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doing so, several large miners have lost over $50,000 dollars worth
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of mining income so far.</p>
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<p>All software that assumes blocks are valid (because invalid blocks
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cost miners money) is at risk of showing transactions as confirmed
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when they really aren't. This particularly affects lightweight (SPV)
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wallets and software such as old versions of Bitcoin Core which have
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been downgraded to SPV-level security by the new BIP66 consensus
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rules.</p>
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<p>The immediate fix, which is well underway as of this writing, is to
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get all miners off of SPV mining and back to full validation (at
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least temporarily). As this progresses, we will reduce our
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current recommendation of waiting {{confs}} extra confirmations to a
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lower number.</p>
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<!--
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<div style="text-align:right">
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<i>This notice last updated: 2015-07-04 06:00 UTC</i>
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</div>
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-->
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