BUIP085: Double spend relaying
Proposer: Gal Buki (@torusJKL)
Submitted on: 2018-02-04
Status: passed


A double spend can happen within the time from the initial broadcast
until the transaction is included in a block. Although this is on
average within 10 minutes at the point of sale we need to know that a
unconfirmed transaction is as safe as possible withing seconds.

Currently double spend transactions are not relayed thus a merchant
might not know that there is a high chance of him not receiving his
transaction. In order to detect double spends those transactions need to
be forwarded by the nodes.


By receiving and forwarding double spend transactions sellers learn
about attempts to defraud them faster and can take appropriate steps.
This will make 0-conf transaction on Bitcoin Cash more safe and will
give it broader acceptance.


  1. Develop a double spend relaying that is compatible with BitcoinXT’s
    implementation (the relaying as such and the rpc call).
  2. Add a double spend visualization in the wallet GUI.


The double spend proof should be developed and to be implemented for
BUCash with the aim of being ready for inclusion in the scheduled
November 2018 protocol upgrade.


The lead developer will have discretion and flexibility to modify
details specified in this BUIP, while keeping within the spirit of the
BUIP with the goal of advancing 0-conf tx security on Bitcoin Cash while
staying compatible with the implementation used by BitcoinXT.


- Relay and alert user to double spends (BitcoinXT