BIP 0078 - Revision history

934: Update BIP text with latest version from https://github.com/bitcoin/bips/blob/83a1afd985984862/bip-0078.mediawiki

2024-10-09T19:25:39Z

Update BIP text with latest version from https://github.com/bitcoin/bips/blob/83a1afd985984862/bip-0078.mediawiki

934: Update BIP text with latest version from https://github.com/bitcoin/bips/blob/51b2d131bea737bc/bip-0078.mediawiki

2024-04-30T21:40:47Z

Update BIP text with latest version from https://github.com/bitcoin/bips/blob/51b2d131bea737bc/bip-0078.mediawiki

← Older revision		Revision as of 21:40, 30 April 2024
Line 147:		Line 147:
	</pre>		</pre>

	* <code>additionalfeeoutputindex=</code>, if the sender is willing to pay for increased fee, this indicate output can have its value ~~substracted~~ to pay for it.		* <code>additionalfeeoutputindex=</code>, if the sender is willing to pay for increased fee, this indicate output can have its value subtracted to pay for it.

	If the <code>additionalfeeoutputindex</code> is out of bounds or pointing to the payment output meant for the receiver, the receiver should ignore the parameter. See [[#fee-output\|fee output]] for more information.		If the <code>additionalfeeoutputindex</code> is out of bounds or pointing to the payment output meant for the receiver, the receiver should ignore the parameter. See [[#fee-output\|fee output]] for more information.
Line 202:		Line 202:

	In some situation, the sender might want to pay some additional fee in the payjoin proposal.		In some situation, the sender might want to pay some additional fee in the payjoin proposal.
	If such is the case, the sender must use both [[#optional-params\|optional parameters]] <code>additionalfeeoutputindex=</code> and <code>maxadditionalfeecontribution=</code> to indicate which output and how much the receiver can ~~substract~~ fee.		If such is the case, the sender must use both [[#optional-params\|optional parameters]] <code>additionalfeeoutputindex=</code> and <code>maxadditionalfeecontribution=</code> to indicate which output and how much the receiver can subtract fee.

	There is several cases where a fee output is useful:		There is several cases where a fee output is useful:
Line 277:		Line 277:
	** Verify that no keypaths is in the PSBT output		** Verify that no keypaths is in the PSBT output
	** If the output is the [[#fee-output\|fee output]]:		** If the output is the [[#fee-output\|fee output]]:
	*** The amount that was ~~substracted~~ from the output's value is less than or equal to <code>maxadditionalfeecontribution</code>. Let's call this amount <code>actual contribution</code>.		*** The amount that was subtracted from the output's value is less than or equal to <code>maxadditionalfeecontribution</code>. Let's call this amount <code>actual contribution</code>.
	*** Make sure the actual contribution is only paying fee: The <code>actual contribution</code> is less than or equals to the difference of absolute fee between the payjoin proposal and the original PSBT.		*** Make sure the actual contribution is only paying fee: The <code>actual contribution</code> is less than or equals to the difference of absolute fee between the payjoin proposal and the original PSBT.
	*** Make sure the actual contribution is only paying for fee incurred by additional inputs: <code>actual contribution</code> is less than or equals to <code>originalPSBTFeeRate * vsize(sender_input_type) * (count(payjoin_proposal_inputs) - count(original_psbt_inputs))</code>. (see [[#fee-output\|Fee output]] section)		*** Make sure the actual contribution is only paying for fee incurred by additional inputs: <code>actual contribution</code> is less than or equals to <code>originalPSBTFeeRate * vsize(sender_input_type) * (count(payjoin_proposal_inputs) - count(original_psbt_inputs))</code>. (see [[#fee-output\|Fee output]] section)
Line 348:		Line 348:
	===<span id="output-substitution"></span>Payment output substitution===		===<span id="output-substitution"></span>Payment output substitution===

	Unless disallowed by sender ~~explicitely~~ via `disableoutputsubstitution=true` or by the BIP21 url via query parameter the `pjos=0`, the receiver is free to decrease the amount, remove, or change the scriptPubKey output paying to himself.		Unless disallowed by sender explicitly via `disableoutputsubstitution=true` or by the BIP21 url via query parameter the `pjos=0`, the receiver is free to decrease the amount, remove, or change the scriptPubKey output paying to himself.
	Note that if payment output substitution is disallowed, the reveiver can still increase the amount of the output. (See [[#reference-impl\|the reference implementation]])		Note that if payment output substitution is disallowed, the reveiver can still increase the amount of the output. (See [[#reference-impl\|the reference implementation]])

Line 417:		Line 417:
	We then prepare <code>originalPSBT</code> from the <code>signedPSBT</code> via the <code>CreateOriginalPSBT</code> function and get back the <code>proposal</code>.		We then prepare <code>originalPSBT</code> from the <code>signedPSBT</code> via the <code>CreateOriginalPSBT</code> function and get back the <code>proposal</code>.

	While we verify the <code>proposal</code>, we also import into it ~~informations~~ about our own inputs and outputs from the <code>signedPSBT</code>.		While we verify the <code>proposal</code>, we also import into it information about our own inputs and outputs from the <code>signedPSBT</code>.
	At the end of this <code>RequestPayjoin</code>, the proposal is verified and ready to be signed.		At the end of this <code>RequestPayjoin</code>, the proposal is verified and ready to be signed.

Line 561:		Line 561:
	{		{
	var actualContribution = feeOutput.Value - proposedPSBTOutput.Value;		var actualContribution = feeOutput.Value - proposedPSBTOutput.Value;
	// The amount that was ~~substracted~~ from the output's value is less than or equal to maxadditionalfeecontribution		// The amount that was subtracted from the output's value is less than or equal to maxadditionalfeecontribution
	if (actualContribution > optionalParameters.MaxAdditionalFeeContribution)		if (actualContribution > optionalParameters.MaxAdditionalFeeContribution)
	throw new PayjoinSenderException("The actual contribution is more than maxadditionalfeecontribution");		throw new PayjoinSenderException("The actual contribution is more than maxadditionalfeecontribution");
Line 646:		Line 646:
	{\| class="wikitable"		{\| class="wikitable"
	!InputScriptType		!InputScriptType
	!~~Orginal~~ PSBT Fee rate		!Original PSBT Fee rate
	!maxadditionalfeecontribution		!maxadditionalfeecontribution
	!additionalfeeoutputindex		!additionalfeeoutputindex

934: Update BIP text with latest version from https://github.com/bitcoin/bips/blob/edffe529056f6dfd/bip-0078.mediawiki

2021-12-15T16:06:01Z

Update BIP text with latest version from https://github.com/bitcoin/bips/blob/edffe529056f6dfd/bip-0078.mediawiki

← Older revision		Revision as of 16:06, 15 December 2021
Line 213:		Line 213:

	If the sender's fee rate is always round, then a blockchain analyst can easily spot the transactions of the sender involving payjoin by checking if, when removing a single input to the suspected payjoin transaction, the resulting fee rate is round.		If the sender's fee rate is always round, then a blockchain analyst can easily spot the transactions of the sender involving payjoin by checking if, when removing a single input to the suspected payjoin transaction, the resulting fee rate is round.
	To prevent this, the sender can agree to pay ~~more~~ more fee so the receiver make sure that the payjoin transaction fee is also round.		To prevent this, the sender can agree to pay more fee so the receiver make sure that the payjoin transaction fee is also round.

	* The sender's transaction is time sensitive.		* The sender's transaction is time sensitive.
Line 233:		Line 233:
	\|P2SH-P2WPKH		\|P2SH-P2WPKH
	\|91		\|91
			\|-
			\|P2TR
			\|58
	\|}		\|}

Line 253:		Line 256:

	The sender should check the payjoin proposal before signing it to prevent a malicious receiver from stealing money.		The sender should check the payjoin proposal before signing it to prevent a malicious receiver from stealing money.

	* Verify that the absolute fee of the payjoin proposal is equals or higher than the original PSBT.		* Verify that the absolute fee of the payjoin proposal is equals or higher than the original PSBT.
	* If the receiver's BIP21 signalled <code>pjos=0</code>, disable payment output substitution.		* If the receiver's BIP21 signalled <code>pjos=0</code>, disable payment output substitution.
Line 276:		Line 279:
	*** The amount that was substracted from the output's value is less than or equal to <code>maxadditionalfeecontribution</code>. Let's call this amount <code>actual contribution</code>.		*** The amount that was substracted from the output's value is less than or equal to <code>maxadditionalfeecontribution</code>. Let's call this amount <code>actual contribution</code>.
	*** Make sure the actual contribution is only paying fee: The <code>actual contribution</code> is less than or equals to the difference of absolute fee between the payjoin proposal and the original PSBT.		*** Make sure the actual contribution is only paying fee: The <code>actual contribution</code> is less than or equals to the difference of absolute fee between the payjoin proposal and the original PSBT.
	*** Make sure the actual contribution is only paying for fee incurred by additional inputs: <code>actual contribution</code> is less than or equals to <code>originalPSBTFeeRate * vsize(sender_input_type) * (count(~~original_psbt_inputs~~) - count(~~payjoin_proposal_inputs~~))</code>. (see [[#fee-output\|Fee output]] section)		*** Make sure the actual contribution is only paying for fee incurred by additional inputs: <code>actual contribution</code> is less than or equals to <code>originalPSBTFeeRate * vsize(sender_input_type) * (count(payjoin_proposal_inputs) - count(original_psbt_inputs))</code>. (see [[#fee-output\|Fee output]] section)
	** If the output is the payment output and payment output substitution is allowed.		** If the output is the payment output and payment output substitution is allowed.
	*** Do not make any check		*** Do not make any check
Line 329:		Line 332:
	The validation (policy and consensus) of the original transaction is optional: a receiver without a full node can decide to create the payjoin transaction and automatically broadcast the original transaction after a timeout of 1 minute, and only verify that it has been propagated in the network.		The validation (policy and consensus) of the original transaction is optional: a receiver without a full node can decide to create the payjoin transaction and automatically broadcast the original transaction after a timeout of 1 minute, and only verify that it has been propagated in the network.

	However, non-interactive receivers (like a payment processor) need to verify the transaction to prevent UTXO probing attacks.		However, non-interactive receivers (like a payment processor) need to verify the transaction to prevent UTXO probing attacks.

	This is not a concern for interactive receivers like Wasabi Wallet, because those receivers can just limit the number of original PSBT proposals of a specific address to one. With such wallets, the attacker has no way to generate new deposit addresses to probe the UTXOs.		This is not a concern for interactive receivers like Wasabi Wallet, because those receivers can just limit the number of original PSBT proposals of a specific address to one. With such wallets, the attacker has no way to generate new deposit addresses to probe the UTXOs.
Line 502:		Line 505:
	throw new PayjoinSenderException("The receiver added non_witness_utxo or witness_utxo to one of our inputs");		throw new PayjoinSenderException("The receiver added non_witness_utxo or witness_utxo to one of our inputs");
	sequences.Add(proposedTxIn.Sequence);		sequences.Add(proposedTxIn.Sequence);

	// Fill up the info from the original PSBT input so we can sign and get fees.		// Fill up the info from the original PSBT input so we can sign and get fees.
	proposedPSBTInput.NonWitnessUtxo = input.SignedPSBTInput.NonWitnessUtxo;		proposedPSBTInput.NonWitnessUtxo = input.SignedPSBTInput.NonWitnessUtxo;
Line 545:		Line 548:
	if (proposedPSBTOutput.HDKeyPaths.Count != 0)		if (proposedPSBTOutput.HDKeyPaths.Count != 0)
	throw new PayjoinSenderException("The receiver added keypaths to an output");		throw new PayjoinSenderException("The receiver added keypaths to an output");
	~~bool isOriginalOutput =~~ originalOutputs.Count > 0 && originalOutputs.Peek().OriginalTxOut.ScriptPubKey == proposedPSBTOutput.ScriptPubKey;		if (originalOutputs.Count == 0)
	if (isOriginalOutput)		continue;
			var originalOutput = originalOutputs.Peek();
			bool isOriginalOutput = originalOutput.OriginalTxOut.ScriptPubKey == proposedPSBTOutput.ScriptPubKey;
			bool substitutedOutput = !isOriginalOutput &&
			allowOutputSubstitution &&
			originalOutput.OriginalTxOut.ScriptPubKey == paymentScriptPubKey;
			if (isOriginalOutput \|\| substitutedOutput)
	{		{
	~~var originalOutput =~~ originalOutputs.Dequeue();		originalOutputs.Dequeue();
	if (output.OriginalTxOut == feeOutput)		if (output.OriginalTxOut == feeOutput)
	{		{
Line 641:		Line 650:
	!additionalfeeoutputindex		!additionalfeeoutputindex
	\|-		\|-
	\|P2SH-~~P2WSH~~		\|P2SH-P2WPKH
	\|2 sat/vbyte		\|2 sat/vbyte
	\|0.00000182		\|0.00000182
Line 664:		Line 673:
	* [[https://github.com/btcpayserver/btcpayserver\|BTCPay Server]] has implemented sender and receiver side of this protocol.		* [[https://github.com/btcpayserver/btcpayserver\|BTCPay Server]] has implemented sender and receiver side of this protocol.
	* [[https://github.com/zkSNACKs/WalletWasabi/\|Wasabi Wallet]] has merged sender's support.		* [[https://github.com/zkSNACKs/WalletWasabi/\|Wasabi Wallet]] has merged sender's support.
	* [[https://github.com/JoinMarket-Org/joinmarket-clientserver\|Join Market]] ~~is in the process~~ of ~~implementing the~~ protocol.		* [[https://github.com/JoinMarket-Org/joinmarket-clientserver\|Join Market]] has implemented sender and receiver side of this protocol.
	* [[https://github.com/bitcoinjs/payjoin-client\|JavaScript sender implementation]].		* [[https://github.com/bitcoinjs/payjoin-client\|JavaScript sender implementation]].

934: Update BIP text with latest version from https://github.com/bitcoin/bips/blob/b4dddbcf75c47cdb/bip-0078.mediawiki

2020-08-04T11:58:05Z

Update BIP text with latest version from https://github.com/bitcoin/bips/blob/b4dddbcf75c47cdb/bip-0078.mediawiki

934: Update BIP text with latest version from https://github.com/bitcoin/bips/blob/c134a853a9fc0657/bip-0078.mediawiki

2020-08-02T07:59:50Z

Update BIP text with latest version from https://github.com/bitcoin/bips/blob/c134a853a9fc0657/bip-0078.mediawiki

Show changes

← Older revision		Revision as of 11:58, 4 August 2020
Line 68:		Line 68:
	In a payjoin payment, the following steps happen:		In a payjoin payment, the following steps happen:

	* The receiver of the payment, presents a [[bip-~~021~~.mediawiki\|BIP 21 URI]] to the sender with a parameter <code>pj=</code> describing a payjoin endpoint.		* The receiver of the payment, presents a [[bip-0021.mediawiki\|BIP 21 URI]] to the sender with a parameter <code>pj=</code> describing a payjoin endpoint.
	* The sender creates a signed, finalized PSBT with witness UTXO or previous transactions of the inputs. We call this PSBT the <code>original</code>.		* The sender creates a signed, finalized PSBT with witness UTXO or previous transactions of the inputs. We call this PSBT the <code>original</code>.
	* The receiver replies back with a signed PSBT containing his own signed inputs/outputs and those of the sender. We call this PSBT <code>Payjoin proposal</code>.		* The receiver replies back with a signed PSBT containing his own signed inputs/outputs and those of the sender. We call this PSBT <code>Payjoin proposal</code>.
Line 125:		Line 125:
	===BIP21 payjoin parameters===		===BIP21 payjoin parameters===

	This proposal is defining the following new [[bip-~~021~~.mediawiki\|BIP 21 URI]] parameters:		This proposal is defining the following new [[bip-0021.mediawiki\|BIP 21 URI]] parameters:
	* <code>pj=</code>: Represents an http(s) endpoint which the sender can POST the original PSBT.		* <code>pj=</code>: Represents an http(s) endpoint which the sender can POST the original PSBT.
	* <code>pjos=0</code>: Signal to the sender that they MUST disallow [[#output-substitution\|payment output substitution]]. (See [[#unsecured-payjoin\|Unsecured payjoin server]])		* <code>pjos=0</code>: Signal to the sender that they MUST disallow [[#output-substitution\|payment output substitution]]. (See [[#unsecured-payjoin\|Unsecured payjoin server]])
Line 669:		Line 669:
	==Backward compatibility==		==Backward compatibility==

	The receivers are advertising payjoin capabilities through [[~~https://github.com/bitcoin/bips/blob/master/~~bip-0021.mediawiki\|BIP21's URI Scheme]].		The receivers are advertising payjoin capabilities through [[bip-0021.mediawiki\|BIP21's URI Scheme]].

	Senders not supporting payjoin will just ignore the <code>pj</code> variable and thus, will proceed to normal payment.		Senders not supporting payjoin will just ignore the <code>pj</code> variable and thus, will proceed to normal payment.
Line 676:		Line 676:

	Special thanks to Kukks for developing the initial support to BTCPay Server, to junderw, AdamISZ, lukechilds, ncoelho, nopara73, lontivero, yahiheb, SomberNight, andrewkozlik, instagibbs, RHavar for all the feedback we received since our first implementation.		Special thanks to Kukks for developing the initial support to BTCPay Server, to junderw, AdamISZ, lukechilds, ncoelho, nopara73, lontivero, yahiheb, SomberNight, andrewkozlik, instagibbs, RHavar for all the feedback we received since our first implementation.
	Thanks again to RHavar who wrote the [[~~https://github.com/bitcoin/bips/blob/master/~~bip-0079.mediawiki\|BIP79 Bustapay]] proposal, this gave a good starting point for our proposal.		Thanks again to RHavar who wrote the [[bip-0079.mediawiki\|BIP79 Bustapay]] proposal, this gave a good starting point for our proposal.