Hello everyone,

We would like to propose a new BIP to extend OP_CSV (and/or OP_CLTV) in
order for these to allow and interpret negative values. This way,
taking the example shown in BIP 112:

HASH160 <revokehash> EQUAL
IF
     <Bob's pubkey>
ELSE
     "24h" CHECKSEQUENCEVERIFY DROP
     <Alice's pubkey>
ENDIF
CHECKSIG

that gives ownership only to Bob for the first 24 hours and then to
whichever spends first, we basically propose using the negative bit value:

HASH160 <revokehash> EQUAL
IF
     <Bob's pubkey>
ELSE
     "-24h" CHECKSEQUENCEVERIFY DROP
     <Alice's pubkey>
ENDIF
CHECKSIG

meaning that both would have ownership for the first 24 hours, but
after that only Bob would own such coins. Its implementation should
not be too tedious, and in fact it simply implies considering negative
values that are at the moment discarded as for the specification of
BIP-112, leaving the sign bit unused.

This, we argue, an increase the fairness of the users, and can at times
be more cost-effective for users to do rather than trying a Replace-By-Fee
transaction, should they want to modify such payment.

We would like to have a discussion about this before proposing the
BIP, for which we are preparing the text.

You can find our paper discussing it here:
https://hal-cea.archives-ouvertes.fr/cea-01867357 (find attached as well)

Best,

-- 
Alejandro Ranchal Pedrosa, Önder Gürcan and Sara Tucci-Piergiovanni