229 lines
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229 lines
14 KiB
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<ol class="chapter"><li class="chapter-item expanded affix "><a href="../index.html">zcashd</a></li><li class="chapter-item expanded "><a href="../user.html"><strong aria-hidden="true">1.</strong> User Documentation</a></li><li><ol class="section"><li class="chapter-item expanded "><a href="../user/release-support.html"><strong aria-hidden="true">1.1.</strong> Release Support</a></li><li class="chapter-item expanded "><a href="../user/platform-support.html"><strong aria-hidden="true">1.2.</strong> Platform Support</a></li><li class="chapter-item expanded "><a href="../user/wallet-backup.html"><strong aria-hidden="true">1.3.</strong> Wallet Backup</a></li><li class="chapter-item expanded "><a href="../user/shield-coinbase.html"><strong aria-hidden="true">1.4.</strong> Shielding Coinbase Outputs</a></li><li class="chapter-item expanded "><a href="../user/files.html"><strong aria-hidden="true">1.5.</strong> Data Directory Structure</a></li><li class="chapter-item expanded "><a href="../user/metrics.html"><strong aria-hidden="true">1.6.</strong> Metrics</a></li><li class="chapter-item expanded "><a href="../user/tor.html"><strong aria-hidden="true">1.7.</strong> Using zcashd with Tor</a></li><li class="chapter-item expanded "><a href="../user/security-warnings.html"><strong aria-hidden="true">1.8.</strong> Security Warnings</a></li><li class="chapter-item expanded "><a href="../user/deprecation.html"><strong aria-hidden="true">1.9.</strong> Deprecated Features</a></li></ol></li><li class="chapter-item expanded "><a href="../dev.html"><strong aria-hidden="true">2.</strong> Developer Documentation</a></li><li><ol class="section"><li class="chapter-item expanded "><a href="../dev/dnsseed-policy.html"><strong aria-hidden="true">2.1.</strong> DNS Seeders</a></li><li class="chapter-item expanded "><a href="../dev/rust.html"><strong aria-hidden="true">2.2.</strong> Rust in zcashd</a></li><li class="chapter-item expanded "><a href="../dev/regtest.html"><strong aria-hidden="true">2.3.</strong> Regtest Tips And Hints</a></li><li class="chapter-item expanded "><a href="../dev/platform-tier-policy.html"><strong aria-hidden="true">2.4.</strong> Platform Tier Policy</a></li><li class="chapter-item expanded "><a href="../dev/deprecation.html"><strong aria-hidden="true">2.5.</strong> Deprecation Procedure</a></li></ol></li><li class="chapter-item expanded "><a href="../design.html"><strong aria-hidden="true">3.</strong> Design</a></li><li><ol class="section"><li class="chapter-item expanded "><a href="../design/chain-state.html"><strong aria-hidden="true">3.1.</strong> Chain State</a></li><li class="chapter-item expanded "><a href="../design/coins-view.html"><strong aria-hidden="true">3.2.</strong> "Coins" View</a></li><li class="chapter-item expanded "><a href="../design/p2p-data-propagation.html" class="active"><strong aria-hidden="true">3.3.</strong> P2P Data Propagation</a></li></ol></li></ol>
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<h1 class="menu-title">The zcashd Book</h1>
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<main>
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<h1 id="p2p-data-propagation"><a class="header" href="#p2p-data-propagation">P2P data propagation</a></h1>
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<p>This page contains notes about how block and transaction data is tracked and propagated by
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<code>zcashd</code>. Most of this behaviour is inherited from Bitcoin Core, but some differences have
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developed.</p>
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<p>Some of this content is duplicated from in-code comments, but assembling this summary in
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one place is generally useful for understanding the overall dynamic :)</p>
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<h2 id="recentrejects"><a class="header" href="#recentrejects"><code>recentRejects</code></a></h2>
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<p>When a transaction is rejected by <code>AcceptToMemoryPool</code>, the transaction is added to the
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<code>recentRejects</code> Bloom filter, so that we don't process it again. The Bloom filter resets
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whenever the chain tip changes, as previously invalid transactions might become valid.</p>
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<p>To prevent DoS attacks against wallets submitting transactions, <code>recentRejects</code> needs to
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store a commitment to the entire transaction. This ensures that if a transaction is
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malleated by a network peer to invalidate its authorizing data, the node will ignore
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future advertisements of that specific transaction, but still request alternative versions
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of the same txid (which might have valid authorizing data).</p>
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<ul>
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<li>For pre-v5 transactions, the txid commits to the entire transaction, and the wtxid is
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the txid with a globally-fixed (all-ones) suffix.</li>
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<li>For v5+ transactions, the wtxid commits to the entire transaction.</li>
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</ul>
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<h2 id="maporphantransactions"><a class="header" href="#maporphantransactions"><code>mapOrphanTransactions</code></a></h2>
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<p>Upstream uses this map to store transactions that are rejected by <code>AcceptToMemoryPool</code>
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because the node doesn't have their transparent inputs. <code>zcashd</code> inherits this behaviour
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but limits it to purely-transparent transactions (that is, if a transaction contains any
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shielded components, the node rejects it as invalid and adds it to <code>recentRejects</code>).</p>
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<p><code>mapOrphanTransactions</code> indexes transactions by txid. This means that if an orphan
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transaction is received (spending transparent UTXOs the node does not know about), and it
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also happens to be invalid for other reasons (subsequent <code>AcceptToMemoryPool</code> rules that
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haven't yet been checked), then the node will not request any v5+ transactions with the
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same txid but different authorizing data. This does not create a DoS problem for wallets,
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because an adversary that manipulated an orphan transaction to be invalid under the above
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constraints would also need to prevent the orphan's parent from entering the mempool, and
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eventually a parent is reached that is not an orphan. Once the orphan's direct parent is
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accepted, the orphan is re-evaluated, and if it had been manipulated to be invalid, its
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wtxid is added to <code>recentRejects</code> while its txid is removed from <code>mapOrphanTransactions</code>,
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enabling the wallet to rebroadcast the unmodified transaction.</p>
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