SIGHASHALL

SIGHASH_ALL, often written as SIGHASH_ALL or SIGHASH_ALL (0x01), is a signature hash type used in Bitcoin to specify what parts of a transaction are covered by a digital signature. When a transaction input is signed with SIGHASH_ALL, the resulting signature commits to the entire transaction’s inputs and outputs, meaning any modification to any input or output would invalidate the signature. This provides strong integrity by ensuring that the funds are directed as originally intended.

How it works in practice: during signing, the transaction is serialized in a specific way depending on the sighash type, and the hash of that serialization is produced. For SIGHASH_ALL, the serialization is constructed so that all inputs and all outputs are included in the hash. The signer then signs this hash with their private key to produce a signature that proves ownership of the referenced funds and authorizes the exact transaction as signed. In standard non-SegWit transactions, this process signs the entire transaction; in SegWit contexts, the exact serialization differs but SIGHASH_ALL still indicates full coverage of inputs and outputs within the signing scheme.

Significance and use: SIGHASH_ALL is the default signing mode for most ordinary Bitcoin transactions, providing strong protection against tampering with any part of the transaction. It can be combined with other flags to alter scope, such as with SIGHASH_ANYONECANPAY to sign only the current input while still signing all outputs, though such combinations change the guarantees provided by the signature.

Related concepts: SIGHASH types also include SIGHASH_NONE and SIGHASH_SINGLE, which sign fewer parts of the transaction, and SIGHASH_ALL combined with SIGHASH_ANYONECANPAY variants. These types determine which portions of the transaction are included in the signature.