BIP 143 — Transaction Signature Verification for Version 0 Witness Program

BIP 143 (Transaction Signature Verification for Version 0 Witness Program) defines the new signature-hash algorithm for SegWit v0 inputs. It removes the quadratic scaling of legacy sighash computation (a denial-of-service vector in large transactions) and commits to the input amount being spent, which simplifies safe signing on hardware wallets. Repository status: Deployed.

Debate relevance: Surfaces in 'what did SegWit actually fix' exchanges — the sighash overhaul is the less famous half of SegWit alongside malleability. Common misstatements: Attributing the quadratic-sighash fix to BIP 141's structure rather than BIP 143's algorithm, or claiming legacy inputs also got the fix — pre-SegWit inputs still use the old algorithm.