I'm requesting feedback for Hash Time-Locked Contract (HTLC) transactions
in Bitcoin.

HTLC transactions allow you to pay for the preimage of a hash. CSV/CLTV can
be used to recover your funds if the other party is not cooperative. These
scripts take the following general form:

    [HASHOP] <digest> OP_EQUAL
    OP_IF
        <seller pubkey>
    OP_ELSE
        <num> [TIMEOUTOP] OP_DROP <buyer pubkey>
    OP_ENDIF
    OP_CHECKSIG

These transactions are useful for both the Lightning network and in
zero-knowledge contingent payments. This very script (using CLTV and
SHA256) was used as part of our "pay-to-sudoku" ZKCP demo earlier this
year: https://github.com/zcash/pay-to-sudoku

Members of the community have expressed the desire for a BIP to submitted
in coordination with changes to Bitcoin Core that support these
transactions in the wallet.

Please review my draft BIP here:
https://gist.github.com/ebfull/8306903041d46e4119a39442f72a3741

An implementation is being worked on here:
https://github.com/bitcoin/bitcoin/pull/7601

Thanks!

Sean Bowe
Zcash