River Intelligence

Sign up for our curated weekly newsletter delivering exclusive market insights to your inbox.

Invest in Bitcoin.

green checkmark

Human Support

green checkmark

Track Performance

green checkmark

Recurring Buys

Transaction ID (txid)


A txid or Transaction ID is a string of letters and numbers that identifies a specific transaction on the blockchain. The string is simply the double SHA-256 hash of a transaction. This hash can be used to look up a transaction on a node or block explorer.

When signing a transaction, it is in fact the txid that is signed. Signing the txid ensures that if any part of the transaction changes, the transaction ID changes, and the signature is rendered invalid.

Technically, a txid is not always a hash of the entire transaction. Since a signature cannot sign itself, signatures are not included in the txid, and thus signatures can be changed after their creation, sometimes without being invalidated. Before SegWit, this allowed a txid to change after the transaction was signed, a problem called transaction malleability.