Crypto glossary
SegWit (Segregated Witness)
SegWit (Segregated Witness) is a Bitcoin upgrade activated in August 2017 that moved signature data out of the transaction ID, fixing transaction malleability.
SegWit separates the witness, meaning the signatures and scripts that prove coins can be spent, from the rest of the transaction data. Because signatures no longer affect the transaction ID, third parties can no longer alter that ID before confirmation, a flaw known as transaction malleability. Witness data is also counted at a discount, replacing the 1 MB block size limit with a weight limit.
SegWit activated as a soft fork in August 2017 after a long dispute over how to scale Bitcoin; the camp that wanted bigger blocks instead created Bitcoin Cash through a hard fork. Fixing malleability was a precondition for the Lightning Network. Native SegWit addresses begin with bc1q.
Spending from SegWit outputs lowers fees, but older address types still work, so adoption took years. The discount on witness data later made room for inscriptions after Taproot, which some users criticise for filling blocks.
Example
Sending bitcoin from a native SegWit (bc1q) address usually costs noticeably less than from an old address starting with 1, because signature data counts at a quarter of its weight.
Related terms
Latest articles on SegWit
- SegWit Wallets Highlight Partial Defense Against Quantum Risk
- Bitmex Announces Support for Native Segwit Adresses-Bech32
- Bitcoin [BTC] Transaction Fees Hit Three-Year Low as Lightning Network, SegWit Help BTC Scale
- Schnorr, the biggest Bitcoin update since SegWit
- Bitcoin’s High Transaction Fees May Have Been Solved With Segwit Adoption
