Explaining SIGHASH

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Sighash, short for Signature Hash, is a concept within the Bitcoin protocol that determines which parts of a transaction are signed. It plays a crucial role in ensuring the security and integrity of the Bitcoin network.

By using different Sighash types, users have control over which parts of a transaction are mutable and which are immutable when they sign it. This flexibility allows for various use cases, such as creating conditional transactions or enabling partial signatures for multi-signature transactions.

Sighash types, such as SIGHASH_ALL, SIGHASH_NONE, SIGHASH_SINGLE, and others, define different signing schemes. These schemes specify which parts of a transaction are committed to, preventing tampering while still allowing different transaction formats.

Each signature has two flags appended at the end:

SIGHASH, which outputs were committed to this signature:

  • ALL (0x01) = all outputs
  • NONE (0x02) = none output
  • SINGLE (0x03) = only the output with same index as this input.

ANYONECANPAY, which inputs were committed to this signature:

  • False (0x00) = all inputs
  • True (0x80) = only this input

Using both flags in conjunction we get 6 possibilities:


BIP-341 (Taproot) introduces a new flag, SIGHASH_DEFAULT (0x00), that works like SIGHASH_ALL but spares one byte on the signature (64 instead of 65 bytes).

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