TERM_DEF // UPGRADES_BIPS / BIP_143_WITNESS_TX_SIG_VERIFICATION
BIP 143 (WITNESS
TX SIG VERIFICATION)
TX SIG VERIFICATION)
BIP 143 (Witness Tx Sig Verification). The SegWit sighash algorithm fixing quadratic-hashing complexity.
This page sits in the Upgrades & BIPs section — The proposal process and the major upgrades that shaped Bitcoin. Read on for what it is, why it exists, how it works under the hood, and what to watch out for.
This page sits in the Upgrades & BIPs section — The proposal process and the major upgrades that shaped Bitcoin. Read on for what it is, why it exists, how it works under the hood, and what to watch out for.
WHAT_BIP_143_WITNESS_TX_SIG_VERIFICATION_IS
BIP 143 (Witness Tx Sig Verification) — at a glance
UPGRADES
BIP 143 — "Witness Tx Sig Verification" is a proposal in the SegWit family, first published in 2016 with status final (fork/">soft fork). The SegWit sighash algorithm fixing quadratic-hashing complexity. Its technical mechanism: BIP-143 sighash digest including amount + prevouts; fixes O(n²) hashing problem. mandatory for every SegWit-v0 signature
Why it exists
DESIGN
BIP 143 (Witness Tx Sig Verification) exists to solve a specific problem: specify how witness signatures commit to value + inputs to prevent rebinding. Without a written, numbered spec, every wallet and node implementer would interpret the requirement differently — and Bitcoin's value depends on every implementation agreeing exactly. BIP-143 is the single source of truth for this concern, so any new client built today can match the behaviour of every client built since 2016.
HOW_IT_WORKS
Mechanism
HOW IT WORKS
Mechanically, BIP-143 bIP-143 sighash digest including amount + prevouts; fixes O(n²) hashing problem. Because this is a soft fork, old software accepts new behaviour without modification — but new behaviour is rejected if old software produces it. Adoption today: mandatory for every SegWit-v0 signature.
1. Author drafts BIP-143 against the BIP-2 template — abstract, motivation, specification, rationale.
2. The text + a reference implementation are posted on the bitcoin-dev list and as a PR to bitcoin/bips.
3. Reviewers tear it apart: ambiguities, security concerns, edge cases, interaction with prior BIPs.
4. Once stable, the BIP editor merges it; it gets a number (BIP-143) and the status "draft" or "proposed".
5. Implementations land in Bitcoin Core / wallets / other clients. For consensus changes: activation parameters chosen.
6. After deployment + adoption, BIP-143 is promoted to "final"; deprecated proposals get "replaced" or "withdrawn".
WORKED_EXAMPLE
BIP-143 — quick reference card
EXAMPLE
BIP number : 143
Title : Witness Tx Sig Verification
Area : SegWit
First published: 2016
Status : final
Fork class : soft
Motivation : specify how witness signatures commit to value + inputs to prevent rebinding.
Mechanism : BIP-143 sighash digest including amount + prevouts; fixes O(n²) hashing problem.
Where it shows up : mandatory for every SegWit-v0 signature.
Read the spec : https://github.com/bitcoin/bips/blob/master/bip-0143.mediawiki
KEY_PROPERTIES
OPT-IN
No authority can force a BIP on anyone. Adoption depends entirely on whether the change is genuinely useful.
NUMBERED
Stable numeric reference — BIP-143 means the same thing across every wallet, miner, and node that has read this spec.
BIP-143 is a soft fork — it changes (or proposes to change) the rules every full node enforces.
DEPLOYED
Implementations of BIP-143 are in production. The behaviour is observable on mainnet today.
COMMON_PITFALLS
Things that catch people out
PITFALLS
- BIP-143 is a soft fork — old clients accept new behaviour but don't enforce it. Validate against an upgraded node to be sure the rule is being checked.
- Don't confuse "draft" / "proposed" / "final" status — read the BIP header before relying on it in production.
- The BIP number is just an editorial counter — it doesn't imply correctness or stability. Always cross-reference with the latest bitcoin/bips repo.
RELATED_CONCEPTS
Other terms from Upgrades & BIPs — click any to read its page:
TERMINOLOGY_INDEX
TERMINOLOGY
BIP 143 (Witness Tx Sig Verification)
The SegWit sighash algorithm fixing quadratic-hashing complexity.
Segregated Witness (SegWit, BIP 141)
The 2017 upgrade separating witness data, fixing tx malleability, and introducing weight units.
Taproot (BIP 341)
Tapscript (BIP 342)
Script-language updates accompanying Taproot — new opcodes, removed limits.
Schnorr (BIP 340)
The Schnorr signature spec adopted by Taproot.
BIP Process
The community workflow for proposing, discussing, and tracking changes to Bitcoin.
Soft Fork Activation
MASF (Miner-Activated Soft Fork)
Activation triggered by miner signaling in block versions.