TERM_DEF // UPGRADES_BIPS / SIGHASH_ANYPREVOUT_BIP_118
SIGHASH_ANYPREVOUT (BIP
118)
118)
SIGHASH_ANYPREVOUT (BIP 118). Proposed sighash flag enabling signatures that don't commit to a specific previous output.
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_SIGHASH_ANYPREVOUT_BIP_118_IS
SIGHASH_ANYPREVOUT (BIP 118) — at a glance
UPGRADES
BIP 118 is a proposal in the Script family, first published in 2017 with status draft (fork/">soft fork). Proposed sighash flag enabling signatures that don't commit to a specific previous output. Its technical mechanism: SIGHASH_ANYPREVOUT — sign script without committing to a specific UTXO. core of eltoo Lightning channel updates; not yet activated
Why it exists
DESIGN
SIGHASH_ANYPREVOUT (BIP 118) exists to solve a specific problem: allow a signature to commit to no input or output, enabling re-binding contracts. 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-118 is the single source of truth for this concern, so any new client built today can match the behaviour of every client built since 2017.
HOW_IT_WORKS
Mechanism
HOW IT WORKS
Mechanically, BIP-118 sIGHASH_ANYPREVOUT — sign script without committing to a specific UTXO. 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: core of eltoo Lightning channel updates; not yet activated.
1. Author drafts BIP-118 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-118) 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-118 is promoted to "final"; deprecated proposals get "replaced" or "withdrawn".
WORKED_EXAMPLE
BIP-118 — quick reference card
EXAMPLE
BIP number : 118
Title : SIGHASH_ANYPREVOUT (BIP 118)
Area : Script
First published: 2017
Status : draft
Fork class : soft
Motivation : allow a signature to commit to no input or output, enabling re-binding contracts.
Mechanism : SIGHASH_ANYPREVOUT — sign script without committing to a specific UTXO.
Where it shows up : core of eltoo Lightning channel updates; not yet activated.
Read the spec : https://github.com/bitcoin/bips/blob/master/bip-0118.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-118 means the same thing across every wallet, miner, and node that has read this spec.
BIP-118 is a soft fork — it changes (or proposes to change) the rules every full node enforces.
DRAFT
BIP-118 is still in draft — reference code may exist but mainnet adoption is partial or pending.
COMMON_PITFALLS
Things that catch people out
PITFALLS
- BIP-118 is still in DRAFT status — its details can change before activation, and any code built against it may need adjustment.
- BIP-118 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
SIGHASH_ANYPREVOUT (BIP 118)
Proposed sighash flag enabling signatures that don't commit to a specific previous output.
Segregated Witness (SegWit, BIP 141)
The 2017 upgrade separating witness-data/">witness data, fixing tx malleability, and introducing weight units.
Taproot (BIP 341)
The 2021 upgrade introducing key-aggregable schnorr-signatures/">Schnorr signatures and Merkleized script trees.
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.