> For the complete documentation index, see [llms.txt](https://hub.bsvblockchain.org/llms.txt). Markdown versions of documentation pages are available by appending `.md` to page URLs; this page is available as [Markdown](https://hub.bsvblockchain.org/wiki/transactions-and-utxos/bitcoin-transactions/sighash-flags.md).

# SIGHASH flags

**SIGHASH flags** are a byte appended to an ECDSA signature in a Bitcoin transaction input that specify which parts of the transaction's inputs and outputs the signature covers. Because the flag controls what a signature actually commits to, different flags allow the same signature scheme to support different transaction construction patterns, such as multi-party contracts, crowdfunding-style transactions, and payment channels. There are three base flags, which can be combined with the ANYONECANPAY modifier:

* **SIGHASH\_ALL (0x01)** - the default. Signs all of the transaction's inputs and outputs. Any change to any input or output after signing invalidates the signature.
* **SIGHASH\_NONE (0x02)** - signs all of the transaction's inputs, but none of the outputs. Outputs can be changed or added after signing without invalidating the signature.
* **SIGHASH\_SINGLE (0x03)** - signs all of the transaction's inputs and only the output at the same index as the input being signed. Other outputs can be changed or added after signing.
* **SIGHASH\_ANYONECANPAY (0x80)** - a modifier that can be combined with any of the above (e.g. SIGHASH\_SINGLE|ANYONECANPAY) to sign only the specific input being signed, rather than all inputs. This allows other parties to add their own inputs to the transaction after signing. In all cases, the input script (scriptSig) of the input being signed is always excluded from the signed message, regardless of which SIGHASH flags are used - see Transaction Malleability for why this matters. For details of how these flags are applied during signature hash calculation, see Legacy Sighash Algorithm.


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