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.
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.
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