[bitcoin-dev] Anti-transaction replay in a hardfork

Johnson Lau jl2012 at xbt.hk
Wed Jan 25 07:42:13 UTC 2017

> On 25 Jan 2017, at 15:29, Natanael <natanael.l at gmail.com> wrote:
> Den 25 jan. 2017 08:22 skrev "Johnson Lau" <jl2012 at xbt.hk <mailto:jl2012 at xbt.hk>>:
> Assuming Alice is paying Bob with an old style time-locked tx. Under your proposal, after the hardfork, Bob is still able to confirm the time-locked tx on both networks. To fulfil your new rules he just needs to send the outputs to himself again (with different tx format). But as Bob gets all the money on both forks, it is already a successful replay
> Why would Alice be sitting on an old-style signed transaction with UTXO:s none of which she controls (paying somebody else), with NO ability to substitute the transaction for one where she DOES control an output, leaving her unable to be the one spending the replay protecting child transaction? 

If Alice still has full control, she is already protected by my proposal, which does not require any protecting child transaction.

But in many cases she may not have full control. Make it clearer, consider that’s actually a 2-of-2 multisig of Alice and Bob, and the time locked tx is sending to Bob. If the time locked tx is unprotected in the first place, Bob will get all the money from both forks anyway, as there is no reason for him to renegotiate with Alice.
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