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60 lines
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60 lines
3.1 KiB
Plaintext
<pre>
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BIP: 339
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Layer: Peer Services
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Title: WTXID-based transaction relay
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Author: Suhas Daftuar <sdaftuar@chaincode.com>
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Comments-Summary: No comments yet.
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Comments-URI: https://github.com/bitcoin/bips/wiki/Comments:BIP-0339
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Status: Final
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Type: Standards Track
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Created: 2020-02-03
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License: BSD-2-Clause
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</pre>
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==Abstract==
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This BIP describes two changes to the p2p protocol to support transaction relay
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based on the BIP 141 wtxid of a transaction, rather than its txid.
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==Motivation==
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Historically, the inv messages sent on the Bitcoin peer-to-peer network to
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announce transactions refer to transactions by their txid, which is a hash of
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the transaction that does not include the witness (see BIP 141). This has been
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the case even since Segregated Witness (BIP 141/143/144) has been adopted by
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the network.
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Not committing to the witness in transaction announcements creates
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inefficiencies: because a transaction's witness can be malleated without
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altering the txid, a node in receipt of a witness transaction that the node
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does not accept will generally still download that same transaction when
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announced by other peers. This is because the alternative -- of not downloading
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a given txid after rejecting a transaction with that txid -- would allow a
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third party to interfere with transaction relay by malleating a transaction's
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witness and announcing the resulting invalid transaction to nodes, preventing
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relay of the valid version of the transaction as well.
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We can eliminate this concern by using the wtxid in place of the txid when
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announcing and fetching transactions.
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==Specification==
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# A new wtxidrelay message is added, which is defined as an empty message where pchCommand == "wtxidrelay".
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# The protocol version of nodes implementing this BIP must be set to 70016 or higher.
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# The wtxidrelay message MUST be sent in response to a version message from a peer whose protocol version is >= 70016 and prior to sending a verack. A wtxidrelay message received after a verack message MUST be ignored or treated as invalid.
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# A new inv type MSG_WTX (0x00000005) is added, for use in both inv messages and getdata requests, indicating that the hash being referenced is a transaction's wtxid. In the case of getdata requests, MSG_WTX implies that the transaction being requested should be serialized with witness as well, as described in BIP 144.
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# After a node has received a wtxidrelay message from a peer, the node MUST use the MSG_WTX inv type when announcing transactions to that peer.
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# After a node has received a wtxidrelay message from a peer, the node SHOULD use a MSG_WTX getdata message to request any announced transactions. A node MAY still request transactions from that peer using MSG_TX getdata messages, such as for transactions not recently announced by that peer (like the parents of recently announced transactions).
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==Backward compatibility==
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As wtxid-based transaction relay is only enabled between peers that both support it, older clients remain fully compatible and interoperable after this change.
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==Implementation==
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https://github.com/bitcoin/bitcoin/pull/18044
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==Copyright==
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This BIP is licensed under the 2-clause BSD license.
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