Contribute even when a sender makes no change #259
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DanGould
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A pure consolidation does not suffer from Unnecessary Input Heuristic. A Payjoin consolidation without sender change still breaks Common Input Heuristic. Allow it.
DanGould
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Avoid UIH for multiple inputs, and just select any input where UIH does not apply.
Inputs naturally come before outputs in bitcoin transactions.
Such one-output transactions pay the base costs to transact and provide an incentive for a receiver to contribute with reduced marginal cost of adding an input rather than an explicit change output. Allowing payjoin sweeps breaks common input heuristic for them. Sweeps with many inputs are common, making ~5.2% or ~54M of ~1.037B monetary, non-coinbase txs. Source monetary non-coinbase transactions count: https://blockchair.com/bitcoin/transactions?q=is_coinbase(false)#f=hash,is_coinbase,time Source sweep transactions count: https://blockchair.com/bitcoin/transactions?s=time(desc)&q=is_coinbase(false),input_count(2..),output_count(1)#f=hash,time
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Since these changes makes sweeps first-class payjoin transactions, make the Requestbuilder recommend the appropriate parameters for sweeps too.
Without this, a sender would sign a receiver transaction that would get stuck.
This was referenced Jul 18, 2024
Closed
This was referenced Aug 16, 2024
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A pure consolidation does not suffer from Unnecessary Input Heuristic. A Payjoin consolidation without sender change still breaks Common Input Heuristic. Allow it.
This is incomplete because the UIH checking should not be happening if only a consolidation is to occur. That does not suffer from change interpretation nor unnecessary input issues because there is no change to interpret, just a single output funded by all necessary inputs.
Supporting sweeps themselves introduce NO API change. It only allows a payjoin to be created with exactly 1 output paying the receiver.
HOWEVER I have taken the liberty to change
RequestBuilder::build_non_incentivisingto take a min_fee_rate as parameter. Without this, a sender could sign and broadcast transactions that have no chance of being mined. I've seen a persistent mempool for months!These are my notes on Unnecessary Input Heuristic that a reviewer may find helpful in understanding the constraints of the
try_preserving_privacyfunction modified here.This ability
should beis tested with both a sender / receiver integration test and data to show that these types of transactions might be ambiguous with existing payment activity (self spends or sweeps to others)Data:
As of Jul 8, 2024, Out of Blockchair's 1,037,565,391 transactions, 53,232,056 of them
transactions that are not Coinbase transactions have exactly one output with a non-zero amount.
This means approximately 5.13% of all transactions are sweeps that might suffer from Common-input heuristic.
Source monetary non-coinbase transactions count: https://blockchair.com/bitcoin/transactions?q=is_coinbase(false)#f=hash,is_coinbase,time
source sweeps: https://blockchair.com/bitcoin/transactions?s=time(desc)&q=output_count(1),is_coinbase(false),fee(1..),input_count(2..),output_total(1..)#f=hash,time,output_total,fee,is_coinbase,output_count,block_id,input_count
Of the transactions in the past year, since height 797844
There have been 175,639,552 transactions and 8,080,966 of them
This means approximately 4.57% of all non-coinbase transactions in the past year are sweeps that might suffer from common input heuristic.
source all non-coinbase: https://blockchair.com/bitcoin/transactions?s=time(desc)&q=is_coinbase(false),fee(1..),block_id(797844..)#f=hash,time,output_total,is_coinbase,block_id,fee,input_count,output_count
source sweeps: https://blockchair.com/bitcoin/transactions?s=time(desc)&q=output_count(1),is_coinbase(false),fee(1..),input_count(2..),output_total(1..),block_id(797844..)#f=hash,time,output_total,is_coinbase,block_id,fee,input_count,output_count