Segregated Witness (SegWit)

Definition

Segregated Witness is a Bitcoin protocol upgrade that separates certain spending-authorization data into a witness structure while changing how transaction capacity is accounted for. Its design introduced block weight and new witness-program output types. For SegWit serialization, the ordinary transaction identifier excludes witness data, while a separate witness transaction identifier commits to it. This addresses important forms of transaction malleability and supports protocols that need more stable transaction references. SegWit does not remove signature checks: the witness still carries information that nodes must validate when the spending rules require it. It also does not make payments anonymous or guarantee lower fees in every situation. Costs depend on the complete transaction structure and prevailing fee rates. Native SegWit addresses use appropriate Bech32-family encodings, but compatibility depends on the witness version and the sender's software rather than on the general SegWit label alone.