Glossary

wtxid

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The witness transaction ID (wtxid) of a transaction is calculated by taking the double SHA-256 hash of a serialized transaction, including its SegWit marker, version, and witness. When a normal txid is calculated, it excludes witness information, and thus if a transaction has no SegWit inputs, its wtxid is identical to its txid.

Wtxids are used by miners to build a Merkle tree, which is included in a output of the coinbase transaction. This removes any malleability of the witness of a transaction once the transaction is included in a block.

Related Terms
Transaction ID (txid)
A txid or Transaction ID is a string of letters and numbers that identify a specific transaction. It can be used to look up a transaction on a node or block explorer.
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Witness
The witness of a transaction is a section of SegWit transactions not included when a transaction is hashed and signed. The witness contains the witnessScripts for all SegWit inputs of a transaction.
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SegWit
Segregated Witness (SegWit) is a soft-fork upgrade to Bitcoin which was activated in 2017. SegWit fixed the problem of transaction malleability, and paved the way for the implementation of the Lightning Network and many other upgrades.
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Merkle Root
The Merkle root is the final node in a Merkle tree. It is a hash which includes the hashes of all transactions in a block.
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