SegWit
scaling · btc
A Bitcoin upgrade that moved signatures into witness data, fixing third-party malleability and changing block capacity.
- Also known as
- Segregated Witness
SegWit, short for Segregated Witness, is a Bitcoin protocol upgrade that moved signature data into a separate "witness" structure. Because the transaction ID no longer commits to the witness in the old way, SegWit mitigates third-party transaction malleability.
SegWit changed Bitcoin’s block accounting from a simple 1 MB serialized limit to block weight, where witness data is discounted. This increased effective capacity for SegWit transactions and introduced witness versions for future script upgrades.
SegWit activated on BTC in August 2017 as a soft fork. It was a central part of the Bitcoin scaling debate: BTC adopted SegWit and later Layer-2 approaches such as Lightning, while Bitcoin Cash split earlier in 2017 and pursued larger base-layer blocks instead.
By fixing malleability for SegWit transactions, the upgrade made payment-channel protocols easier to build safely. It also created a versioned witness framework later used by Taproot.
Related terms
Bitcoin (BTC)
→The first widely adopted cryptocurrency, using proof of work and an issuance schedule capped near 21 million BTC under current rules.
cryptocurrency · btc
Bitcoin Improvement Proposal (BIP)
→A published proposal or information document for Bitcoin protocols, applications, or community processes.
governance · technology
Transaction
→A serialized state transition that a blockchain can validate, relay, and include in a block.
blockchain · technical
Lightning Network
→A Bitcoin payment-channel network that routes off-chain balance updates and settles channel state on-chain.
bitcoin · layer-2 · payments
Fork
→A fork is a blockchain divergence caused by competing blocks, software changes, or incompatible consensus rules.
blockchain · event