Difference between revisions of "SIGHASH flags"

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Signature checking is flexible because the form of transaction that is signed can be controlled through the use of SIGHASH flags, which are stuck on the end of a signature. In this way, contracts can be constructed in which each party signs only a part of it, allowing other parts to be changed without their involvement. The SIGHASH flags have two parts, a mode and the ANYONECANPAY modifier:
+
A SIGHASH [[flag]] is used to indicate which part of the transaction is signed by the [[Elliptic Curve Digital Signature Algorithm| ECDSA signature]]. The mechanism provides a flexibility in constructing transactions. There are in total 6 different flag combinations that can be added to a digital signature in a transaction. Note that different inputs can use different SIGHASH flags enabling complex compositions of spending conditions.
  
−
SIGHASH_ALL: This is the default. It indicates that everything about the transaction is signed, except for the input scripts. Signing the input scripts as well would obviously make it impossible to construct a transaction, so they are always blanked out. Note, though, that other properties of the input, like the connected output and sequence numbers, are signed; it's only the scripts that are not. Intuitively, it means "I agree to put my money in, if everyone puts their money in and the outputs are this".
+
'''NOTE: Currently all BitcoinSV transactions require an additional SIGHASH flag called SIGHASH_FORKID which is 0x40'''
−
SIGHASH_NONE: The outputs are not signed and can be anything. Use this to indicate "I agree to put my money in, as long as everyone puts their money in, but I don't care what's done with the output". This mode allows others to update the transaction by changing their inputs sequence numbers.
 
−
SIGHASH_SINGLE: Like SIGHASH_NONE, the inputs are signed, but the sequence numbers are blanked, so others can create new versions of the transaction. However, the only output that is signed is the one at the same position as the input. Use this to indicate "I agree, as long as my output is what I want; I don't care about the others".
 
−
The SIGHASH_ANYONECANPAY modifier can be combined with the above three modes. When set, only that input is signed and the other inputs can be anything.
 
  
−
Scripts can contain the CHECKMULTISIG opcode. This opcode provides n-of-m checking: you provide multiple public keys, and specify the number of valid signatures that must be present. The number of signatures can be less than the number of public keys. An output can require two signatures to be spent by setting it to something like this:
+
{| class="wikitable"
 +
|-
 +
! Flag
 +
! Value including SIGHASH_FORKID </br> HEX / BINARY
 +
! Value excluding SIGHASH_FORKID </br> HEX / BINARY
 +
! Functional Meaning
 +
|-
 +
| SIGHASH_ALL
 +
| style="text-align: center;" | 0x41 / 0100 0001
 +
| style="text-align: center;" | 0x01 / 0000 0001
 +
| Sign all inputs and outputs
 +
|-
 +
| SIGHASH_NONE
 +
| style="text-align: center;" | 0x42 / 0100 0010
 +
| style="text-align: center;" | 0x02 / 0000 0010
 +
| Sign all inputs and no output
 +
|-
 +
| SIGHASH_SINGLE
 +
| style="text-align: center;" | 0x43 / 0100 0011
 +
| style="text-align: center;" | 0x03 / 0000 0011
 +
| Sign all inputs and the output with the same index
 +
|-
 +
| SIGHASH_ALL <nowiki>|</nowiki> ANYONECANPAY
 +
| style="text-align: center;" | 0xC1 / 1100 0001
 +
| style="text-align: center;" | 0x81 / 1000 0001
 +
| Sign its own input and all outputs
 +
|-
 +
| SIGHASH_NONE <nowiki>|</nowiki> ANYONECANPAY
 +
| style="text-align: center;" | 0xC2 / 1100 0010
 +
| style="text-align: center;" | 0x82 / 1000 0010
 +
| Sign its own input and no output
 +
|-
 +
| SIGHASH_SINGLE <nowiki>|</nowiki> ANYONECANPAY
 +
| style="text-align: center;" | 0xC3 / 1100 0011
 +
| style="text-align: center;" | 0x83 / 1000 0011
 +
| Sign its own input and the output with the same index
 +
|}
  
−
2 <pubkey1> <pubkey2> 2 CHECKMULTISIGVERIFY
 
−
There are two general patterns for safely creating contracts:
 
  
−
Transactions are passed around outside of the P2P network, in partially-complete or invalid forms.
+
The tables below illustrate what is signed and what is not signed in an ECDSA siganture depending on the SIGHASH type used.
−
Two transactions are used: one (the contract) is created and signed but not broadcast right away. Instead, the other transaction (the payment) is broadcast after the contract is agreed to lock in the money, and then the contract is broadcast.
 
−
This is to ensure that people always know what they are agreeing to.
 
  
−
Together, these features let us build interesting new financial tools on top of the block chain.
+
==Items that are ''always'' signed==
 +
 
 +
The signature on any input always signs the [[TXID]] and [[VOUT]] that comprise the Outpoint being spent as well as the [[Version|version]] of the protocol that the transaction is being evaluated under and the [[nLocktime|locktime]] being applied to the transaction.
 +
 
 +
{| class="wikitable" style="text-align: center;"
 +
|colspan="4" style="font-style: italic; width: 600px;"|TxID
 +
|-
 +
|colspan="4" style="background: #abebc6;"|Version
 +
|-
 +
|colspan="4" style="background: #abebc6;"|Locktime
 +
|-
 +
|colspan="2" style="width: 50%;"|Inputs
 +
|colspan="2" style="width: 50%;"|Outputs
 +
|-
 +
|
 +
|style="font-style: italic;"|Unlocking Script
 +
|
 +
|style="font-style: italic;"|Locking Script
 +
|- style="height: 7em;"
 +
|style="background-color:#abebc6; font-style: italic;"|Outpoint A
 +
|.....Sig Pa, Tx.....
 +
|Xa BSV
 +
|[ChecksigP1]
 +
|- style="height: 7em;"
 +
|style="font-style: italic;"|Outpoint B
 +
|.....Sig Pb, Tx.....
 +
|Xb BSV
 +
|[ChecksigP2]
 +
|-
 +
|style="font-style: bold;"|...
 +
|style="font-style: bold;"|...
 +
|style="font-style: bold;"|...
 +
|style="font-style: bold;"|...
 +
|- style="height: 7em;"
 +
|style="font-style: italic;"|Outpoint N
 +
|.....Sig PN, Tx.....
 +
|XN BSV
 +
|[ChecksigPm]
 +
|}
 +
 
 +
==Items that are ''never'' signed==
 +
 
 +
Unlocking scripts are ''never'' signed
 +
 
 +
{| class="wikitable" style="text-align: center;"
 +
|colspan="4" style="font-style: italic; width: 600px;"|TxID
 +
|-
 +
|colspan="4"|Version
 +
|-
 +
|colspan="4"|Locktime
 +
|-
 +
|colspan="2" style="width: 50%;"|Inputs
 +
|colspan="2" style="width: 50%;"|Outputs
 +
|-
 +
|
 +
|style="font-style: italic;"|Unlocking Script
 +
|
 +
|style="font-style: italic;"|Locking Script
 +
|- style="height: 7em;"
 +
|style="font-style: italic;"|Outpoint A
 +
|style="background: #f5b7b1;"|.....Sig Pa, Tx.....
 +
|Xa BSV
 +
|[ChecksigP1]
 +
|- style="height: 7em;"
 +
|style="font-style: italic;"|Outpoint B
 +
|style="background: #f5b7b1;"|.....Sig Pb, Tx.....
 +
|Xb BSV
 +
|[ChecksigP2]
 +
|-
 +
|style="font-style: bold;"|...
 +
|style="font-style: bold; background: #f5b7b1;"|...
 +
|style="font-style: bold;"|...
 +
|style="font-style: bold;"|...
 +
|- style="height: 7em;"
 +
|style="font-style: italic;"|Outpoint N
 +
|style="background: #f5b7b1;"|.....Sig PN, Tx.....
 +
|XN BSV
 +
|[ChecksigPm]
 +
|}
 +
 
 +
==SIGHASH_ALL==
 +
 
 +
SIGHASH_ALL  signs all inputs and outputs used to build the transaction. Once an input signed with SIGHASH_ALL is added to a transaction, the transaction's details cannot be changed without that signature being invalidated.
 +
 
 +
{| class="wikitable" style="text-align: center;"
 +
|colspan="4" style="font-style: italic; width: 600px;"|TxID
 +
|-
 +
|colspan="4" style="background: #abebc6;"|Version
 +
|-
 +
|colspan="4" style="background: #abebc6;"|Locktime
 +
|-
 +
|colspan="2" style="width: 50%;"|Inputs
 +
|colspan="2" style="width: 50%;"|Outputs
 +
|-
 +
|
 +
|style="font-style: italic;"|Unlocking Script
 +
|
 +
|style="font-style: italic;"|Locking Script
 +
|- style="height: 7em;"
 +
|style="background-color:#abebc6; font-style: italic;"|Outpoint A
 +
|.....Sig Pa, Tx.....
 +
|style="background-color:#abebc6;"|Xa BSV
 +
|style="background-color:#abebc6;"|[ChecksigP1]
 +
|- style="height: 7em;"
 +
|style="background-color:#abebc6;font-style: italic;"|Outpoint B
 +
|.....Sig Pb, Tx.....
 +
|style="background-color:#abebc6"|Xb BSV
 +
|style="background-color:#abebc6"|[ChecksigP2]
 +
|-
 +
|style="font-style: bold; background-color:#abebc6;"|...
 +
|style="font-style: bold;"|...
 +
|style="font-style: bold; background-color:#abebc6;"|...
 +
|style="font-style: bold; background-color:#abebc6;"|...
 +
|- style="height: 7em;"
 +
|style="background-color:#abebc6; font-style: italic;"|Outpoint N
 +
|.....Sig PN, Tx.....
 +
|style="background-color:#abebc6"|XN BSV
 +
|style="background-color:#abebc6"|[ChecksigPm]
 +
|}
 +
 
 +
==SIGHASH_SINGLE==
 +
 
 +
SIGHASH_SINGLE  signs all inputs and the output that shares the same index as the input being signed. If that output or any inputs are changed that signature becomes invalidated.
 +
 
 +
{| class="wikitable" style="text-align: center;"
 +
|colspan="4" style="font-style: italic; width: 600px;"|TxID
 +
|-
 +
|colspan="4" style="background: #abebc6;"|Version
 +
|-
 +
|colspan="4" style="background: #abebc6;"|Locktime
 +
|-
 +
|colspan="2" style="width: 50%;"|Inputs
 +
|colspan="2" style="width: 50%;"|Outputs
 +
|-
 +
|
 +
|style="font-style: italic;"|Unlocking Script
 +
|
 +
|style="font-style: italic;"|Locking Script
 +
|- style="height: 7em;"
 +
|style="background-color:#abebc6; font-style: italic;"|Outpoint A
 +
|.....Sig Pa, Tx.....
 +
|style="background-color:#abebc6;"|Xa BSV
 +
|style="background-color:#abebc6;"|[ChecksigP1]
 +
|- style="height: 7em;"
 +
|style="background-color:#abebc6;font-style: italic;"|Outpoint B
 +
|.....Sig Pb, Tx.....
 +
|Xb BSV
 +
|[ChecksigP2]
 +
|-
 +
|style="font-style: bold; background-color:#abebc6;"|...
 +
|style="font-style: bold;"|...
 +
|style="font-style: bold;"|...
 +
|style="font-style: bold;"|...
 +
|- style="height: 7em;"
 +
|style="background-color:#abebc6; font-style: italic;"|Outpoint N
 +
|.....Sig PN, Tx.....
 +
|XN BSV
 +
|[ChecksigPm]
 +
|}
 +
 
 +
==SIGHASH_NONE==
 +
 
 +
SIGHASH_NONE  signs all inputs and no outputs. Any output can be changed without invalidating the signature however if any inputs are changed that signature becomes invalidated.
 +
 
 +
{| class="wikitable" style="text-align: center;"
 +
|colspan="4" style="font-style: italic; width: 600px;"|TxID
 +
|-
 +
|colspan="4" style="background: #abebc6;"|Version
 +
|-
 +
|colspan="4" style="background: #abebc6;"|Locktime
 +
|-
 +
|colspan="2" style="width: 50%;"|Inputs
 +
|colspan="2" style="width: 50%;"|Outputs
 +
|-
 +
|
 +
|style="font-style: italic;"|Unlocking Script
 +
|
 +
|style="font-style: italic;"|Locking Script
 +
|- style="height: 7em;"
 +
|style="background-color:#abebc6; font-style: italic;"|Outpoint A
 +
|.....Sig Pa, Tx.....
 +
|Xa BSV
 +
|[ChecksigP1]
 +
|- style="height: 7em;"
 +
|style="background-color:#abebc6;font-style: italic;"|Outpoint B
 +
|.....Sig Pb, Tx.....
 +
|Xb BSV
 +
|[ChecksigP2]
 +
|-
 +
|style="font-style: bold; background-color:#abebc6;"|...
 +
|style="font-style: bold;"|...
 +
|style="font-style: bold;"|...
 +
|style="font-style: bold;"|...
 +
|- style="height: 7em;"
 +
|style="background-color:#abebc6; font-style: italic;"|Outpoint N
 +
|.....Sig PN, Tx.....
 +
|XN BSV
 +
|[ChecksigPm]
 +
|}
 +
 
 +
==SIGHASH_ALL|ANYONECANPAY==
 +
 
 +
`Once an input signed with SIGHASH_ALL|ANYONECANPAY is added to a transaction outputs cannot be changed or added without that signature being invalidated.
 +
 
 +
{| class="wikitable" style="text-align: center;"
 +
|colspan="4" style="font-style: italic; width: 600px;"|TxID
 +
|-
 +
|colspan="4" style="background: #abebc6;"|Version
 +
|-
 +
|colspan="4" style="background: #abebc6;"|Locktime
 +
|-
 +
|colspan="2" style="width: 50%;"|Inputs
 +
|colspan="2" style="width: 50%;"|Outputs
 +
|-
 +
|
 +
|style="font-style: italic;"|Unlocking Script
 +
|
 +
|style="font-style: italic;"|Locking Script
 +
|- style="height: 7em;"
 +
|style="background-color:#abebc6; font-style: italic;"|Outpoint A
 +
|.....Sig Pa, Tx.....
 +
|style="background-color:#abebc6;"|Xa BSV
 +
|style="background-color:#abebc6;"|[ChecksigP1]
 +
|- style="height: 7em;"
 +
|style="font-style: italic;"|Outpoint B
 +
|.....Sig Pb, Tx.....
 +
|style="background-color:#abebc6"|Xb BSV
 +
|style="background-color:#abebc6"|[ChecksigP2]
 +
|-
 +
|style="font-style: bold;"|...
 +
|style="font-style: bold;"|...
 +
|style="font-style: bold; background-color:#abebc6;"|...
 +
|style="font-style: bold; background-color:#abebc6;"|...
 +
|- style="height: 7em;"
 +
|style="font-style: italic;"|Outpoint N
 +
|.....Sig PN, Tx.....
 +
|style="background-color:#abebc6"|XN BSV
 +
|style="background-color:#abebc6"|[ChecksigPm]
 +
|}
 +
 
 +
==SIGHASH_SINGLE|ANYONECANPAY==
 +
 
 +
SIGHASH_SINGLE|ANYONECANPAY signs the input being signed and the output that shares the same index. If that output is changed that signature becomes invalidated.
 +
 
 +
{| class="wikitable" style="text-align: center;"
 +
|colspan="4" style="font-style: italic; width: 600px;"|TxID
 +
|-
 +
|colspan="4" style="background: #abebc6;"|Version
 +
|-
 +
|colspan="4" style="background: #abebc6;"|Locktime
 +
|-
 +
|colspan="2" style="width: 50%;"|Inputs
 +
|colspan="2" style="width: 50%;"|Outputs
 +
|-
 +
|
 +
|style="font-style: italic;"|Unlocking Script
 +
|
 +
|style="font-style: italic;"|Locking Script
 +
|- style="height: 7em;"
 +
|style="background-color:#abebc6; font-style: italic;"|Outpoint A
 +
|.....Sig Pa, Tx.....
 +
|style="background-color:#abebc6;"|Xa BSV
 +
|style="background-color:#abebc6;"|[ChecksigP1]
 +
|- style="height: 7em;"
 +
|style="font-style: italic;"|Outpoint B
 +
|.....Sig Pb, Tx.....
 +
|Xb BSV
 +
|[ChecksigP2]
 +
|-
 +
|style="font-style: bold;"|...
 +
|style="font-style: bold;"|...
 +
|style="font-style: bold;"|...
 +
|style="font-style: bold;"|...
 +
|- style="height: 7em;"
 +
|style="font-style: italic;"|Outpoint N
 +
|.....Sig PN, Tx.....
 +
|XN BSV
 +
|[ChecksigPm]
 +
|}
 +
 
 +
==SIGHASH_NONE|ANYONECANPAY==
 +
 
 +
SIGHASH_NONE|ANYONECANPAY signs a single inputs and no outputs. This type of signature can be used to easily assign funds to a person or smart-contract without creating an on-chain action.
 +
 
 +
{| class="wikitable" style="text-align: center;"
 +
|colspan="4" style="font-style: italic; width: 600px;"|TxID
 +
|-
 +
|colspan="4" style="background: #abebc6;"|Version
 +
|-
 +
|colspan="4" style="background: #abebc6;"|Locktime
 +
|-
 +
|colspan="2" style="width: 50%;"|Inputs
 +
|colspan="2" style="width: 50%;"|Outputs
 +
|-
 +
|
 +
|style="font-style: italic;"|Unlocking Script
 +
|
 +
|style="font-style: italic;"|Locking Script
 +
|- style="height: 7em;"
 +
|style="background-color:#abebc6; font-style: italic;"|Outpoint A
 +
|.....Sig Pa, Tx.....
 +
|Xa BSV
 +
|[ChecksigP1]
 +
|- style="height: 7em;"
 +
|style="font-style: italic;"|Outpoint B
 +
|.....Sig Pb, Tx.....
 +
|Xb BSV
 +
|[ChecksigP2]
 +
|-
 +
|style="font-style: bold;"|...
 +
|style="font-style: bold;"|...
 +
|style="font-style: bold;"|...
 +
|style="font-style: bold;"|...
 +
|- style="height: 7em;"
 +
|style="font-style: italic;"|Outpoint N
 +
|.....Sig PN, Tx.....
 +
|XN BSV
 +
|[ChecksigPm]
 +
|}
 +
 
 +
==Use cases==
 +
SIGHASH flags are useful when constructing smart contracts and negotiable transactions in payment channels. 
 +
 
 +
 
 +
===Use Case 1 - Crowdfunding===
 +
Using ALL <nowiki>|</nowiki> ANYONECANPAY allows a transaction to have a fixed output or fixed outputs while keeping the input list open. That is, anyone can add their input with their signature to the transaction without invalidating all existing signatures.
 +
 
 +
 
 +
===Use Case 2 - Blank Check===
 +
Using NONE allows anyone to add their desired outputs to the transaction to claim the funds in the input.
 +
 
 +
 
 +
===Use Case 3 - Modular Transaction===
 +
Using SINGLE <nowiki>|</nowiki> ANYONECANPAY modularises a transaction. Any number of these transactions can be combined into one transaction.
 +
 
 +
==References==
 +
https://github.com/bitcoin-sv/bitcoin-sv/blob/master/src/script/sighashtype.h

Latest revision as of 05:42, 21 April 2022

A SIGHASH flag is used to indicate which part of the transaction is signed by the ECDSA signature. The mechanism provides a flexibility in constructing transactions. There are in total 6 different flag combinations that can be added to a digital signature in a transaction. Note that different inputs can use different SIGHASH flags enabling complex compositions of spending conditions.

NOTE: Currently all BitcoinSV transactions require an additional SIGHASH flag called SIGHASH_FORKID which is 0x40

Flag Value including SIGHASH_FORKID
HEX / BINARY 		Value excluding SIGHASH_FORKID
HEX / BINARY 		Functional Meaning
SIGHASH_ALL 0x41 / 0100 0001 0x01 / 0000 0001 Sign all inputs and outputs
SIGHASH_NONE 0x42 / 0100 0010 0x02 / 0000 0010 Sign all inputs and no output
SIGHASH_SINGLE 0x43 / 0100 0011 0x03 / 0000 0011 Sign all inputs and the output with the same index
SIGHASH_ALL | ANYONECANPAY 0xC1 / 1100 0001 0x81 / 1000 0001 Sign its own input and all outputs
SIGHASH_NONE | ANYONECANPAY 0xC2 / 1100 0010 0x82 / 1000 0010 Sign its own input and no output
SIGHASH_SINGLE | ANYONECANPAY 0xC3 / 1100 0011 0x83 / 1000 0011 Sign its own input and the output with the same index


The tables below illustrate what is signed and what is not signed in an ECDSA siganture depending on the SIGHASH type used.

Items that are always signed

The signature on any input always signs the TXID and VOUT that comprise the Outpoint being spent as well as the version of the protocol that the transaction is being evaluated under and the locktime being applied to the transaction.

TxID
Version
Locktime
Inputs Outputs
Unlocking Script Locking Script
Outpoint A .....Sig Pa, Tx..... Xa BSV [ChecksigP1]
Outpoint B .....Sig Pb, Tx..... Xb BSV [ChecksigP2]
... ... ... ...
Outpoint N .....Sig PN, Tx..... XN BSV [ChecksigPm]

Items that are never signed

Unlocking scripts are never signed

TxID
Version
Locktime
Inputs Outputs
Unlocking Script Locking Script
Outpoint A .....Sig Pa, Tx..... Xa BSV [ChecksigP1]
Outpoint B .....Sig Pb, Tx..... Xb BSV [ChecksigP2]
... ... ... ...
Outpoint N .....Sig PN, Tx..... XN BSV [ChecksigPm]

SIGHASH_ALL

SIGHASH_ALL signs all inputs and outputs used to build the transaction. Once an input signed with SIGHASH_ALL is added to a transaction, the transaction's details cannot be changed without that signature being invalidated.

TxID
Version
Locktime
Inputs Outputs
Unlocking Script Locking Script
Outpoint A .....Sig Pa, Tx..... Xa BSV [ChecksigP1]
Outpoint B .....Sig Pb, Tx..... Xb BSV [ChecksigP2]
... ... ... ...
Outpoint N .....Sig PN, Tx..... XN BSV [ChecksigPm]

SIGHASH_SINGLE

SIGHASH_SINGLE signs all inputs and the output that shares the same index as the input being signed. If that output or any inputs are changed that signature becomes invalidated.

TxID
Version
Locktime
Inputs Outputs
Unlocking Script Locking Script
Outpoint A .....Sig Pa, Tx..... Xa BSV [ChecksigP1]
Outpoint B .....Sig Pb, Tx..... Xb BSV [ChecksigP2]
... ... ... ...
Outpoint N .....Sig PN, Tx..... XN BSV [ChecksigPm]

SIGHASH_NONE

SIGHASH_NONE signs all inputs and no outputs. Any output can be changed without invalidating the signature however if any inputs are changed that signature becomes invalidated.

TxID
Version
Locktime
Inputs Outputs
Unlocking Script Locking Script
Outpoint A .....Sig Pa, Tx..... Xa BSV [ChecksigP1]
Outpoint B .....Sig Pb, Tx..... Xb BSV [ChecksigP2]
... ... ... ...
Outpoint N .....Sig PN, Tx..... XN BSV [ChecksigPm]

SIGHASH_ALL|ANYONECANPAY

`Once an input signed with SIGHASH_ALL|ANYONECANPAY is added to a transaction outputs cannot be changed or added without that signature being invalidated.

TxID
Version
Locktime
Inputs Outputs
Unlocking Script Locking Script
Outpoint A .....Sig Pa, Tx..... Xa BSV [ChecksigP1]
Outpoint B .....Sig Pb, Tx..... Xb BSV [ChecksigP2]
... ... ... ...
Outpoint N .....Sig PN, Tx..... XN BSV [ChecksigPm]

SIGHASH_SINGLE|ANYONECANPAY

SIGHASH_SINGLE|ANYONECANPAY signs the input being signed and the output that shares the same index. If that output is changed that signature becomes invalidated.

TxID
Version
Locktime
Inputs Outputs
Unlocking Script Locking Script
Outpoint A .....Sig Pa, Tx..... Xa BSV [ChecksigP1]
Outpoint B .....Sig Pb, Tx..... Xb BSV [ChecksigP2]
... ... ... ...
Outpoint N .....Sig PN, Tx..... XN BSV [ChecksigPm]

SIGHASH_NONE|ANYONECANPAY

SIGHASH_NONE|ANYONECANPAY signs a single inputs and no outputs. This type of signature can be used to easily assign funds to a person or smart-contract without creating an on-chain action.

TxID
Version
Locktime
Inputs Outputs
Unlocking Script Locking Script
Outpoint A .....Sig Pa, Tx..... Xa BSV [ChecksigP1]
Outpoint B .....Sig Pb, Tx..... Xb BSV [ChecksigP2]
... ... ... ...
Outpoint N .....Sig PN, Tx..... XN BSV [ChecksigPm]

Use cases

SIGHASH flags are useful when constructing smart contracts and negotiable transactions in payment channels.


Use Case 1 - Crowdfunding

Using ALL | ANYONECANPAY allows a transaction to have a fixed output or fixed outputs while keeping the input list open. That is, anyone can add their input with their signature to the transaction without invalidating all existing signatures.


Use Case 2 - Blank Check

Using NONE allows anyone to add their desired outputs to the transaction to claim the funds in the input.


Use Case 3 - Modular Transaction

Using SINGLE | ANYONECANPAY modularises a transaction. Any number of these transactions can be combined into one transaction.

References

https://github.com/bitcoin-sv/bitcoin-sv/blob/master/src/script/sighashtype.h

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