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sighash-types.md

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Sighash types

This note is about signature hashing types.

In src/script/interpreter.h:

/** Signature hash types/flags */
enum
{
    SIGHASH_ALL = 1,
    SIGHASH_NONE = 2,
    SIGHASH_SINGLE = 3,
    SIGHASH_ANYONECANPAY = 0x80,
};

In src/script/interpreter.cpp:

template <class T>
uint256 SignatureHash(const CScript& scriptCode, const T& txTo, unsigned int nIn, int nHashType, const CAmount& amount, SigVersion sigversion, const PrecomputedTransactionData* cache)

This does the work of selecting which parts of a transaction to hash/serialize and sign. int nHashType is what holds the sighash types.

sig hash type inputs (prevouts) inputs (sequence no) outputs what we sign what can change
SIGHASH_ALL only 0b00000001 ALL ALL ALL all inputs and outputs in this tx. this is the default. NOTHING
SIGHASH_NONE only 0b00000010 ALL this input NONE all inputs and no outputs any outputs
SIGHASH_SINGLE 0b00000011 ALL this input same index as this input all inputs and one output (same index as this one) other outputs
SIGHASH_ALL | SIGHASH_ANYONECANPAY 0b10000001 this input this input ALL one input and all outputs. you and others are contributing inputs, and all you care is that the outputs don't change. others' inputs
SIGHASH_NONE | SIGHASH_ANYONECANPAY 0b10000010 this input this input NONE one input and no outputs you are contributing an input that can be in any tx and can spend to any address(es). other inputs and any of the outputs
SIGHASH_SINGLE | SIGHASH_ANYONECANPAY 0b10000011 this input this input same index as this input one input and one output. you are contributing an input and care about 1 output. other inputs and other outputs