[bitcoin-dev] Fix or withdraw BIP120/121?

[Kalle Rosenbaum via bitcoin-dev]

Hi

There is an inherent problem with BIP120, Proof of Payment: If there
is a soft fork, a server that verifies PoPs will accept a PoP as valid
without checking any of the new Bitcoin rules.

For example, a server will be fooled by a segwit transaction, because
the server doesn't have a witness to verify and consequently will
accept any PoP with an empty scriptSig.

Besides this problem, on-chain payments are not hot anymore and
interest, or need, for PoP as a concept seems low.

I have no good solution for the soft fork problem. Requiring all
software that uses PoP to upgrade to a new PoP specification on each
soft-fork is not good enough. Do you have any ideas on how to fix it?

If there is no good solution to the soft-fork issue, I suggest that I
withdraw BIP120 and BIP121.

As for current implementations: I know that Mycelium implements
BIP120, but I'm not sure if there is any other software, besides my
own, implementing it. If you know of any, please let me know so I can
discuss it with them.

Regards,
/Kalle