I find another proposed use of CODESEPARATOR here: https://lists.linuxfoundation.org/pipermail/lightning-dev/2016-March/000455.html <https://lists.linuxfoundation.org/pipermail/lightning-dev/2016-March/000455.html>
<KeyA> OP_CHECKSIG OP_IF <KeyB> OP_ELSE <Delay> OP_CSV OP_DROP OP_CODESEPARATOR <KeyA> OP_ENDIF OP_CHECKSIG It is actually 2 scripts: S1: <KeyA> OP_CHECKSIGVERIFY <KeyB> OP_CHECKSIG S2: <Delay> OP_CSV OP_DROP <KeyA> OP_CHECKSIG Under taproot, we could make Q = P + H(P||S2)G, where P = MuSig(KeyA, KeyB) S1 becomes a direct spending with Q, and there is no need to use OP_IF or CODESEPARATOR in S2 at all. ================== If it is only to force R reuse, there is no need to use CODESEPARATOR: Input: <R> <S2> <S1> Script: 2DUP EQUAL NOT VERIFY 2 PICK SWAP CAT <key> DUP TOALTSTACK CHECKSIGVERIFY CAT FROMALTSTACK CHECKSIG But using CODESEPARATOR will save 3 bytes Input: <S2> <R> <S1> Script: OVER SWAP CAT <key> DUP TOALTSTACK CHECKSIGVERIFY CODESEPARATOR SWAP CAT FROMALTSTACK CHECKSIG However, a much better way would be: Input: <S> Script: <known R> SWAP CAT <key> CHECKSIG The discrete log of R could be a shared secret between A and B. If the purpose is to publish the private key to the whole world, R = G could be used. > On 24 Dec 2018, at 8:01 PM, ZmnSCPxj <zmnsc...@protonmail.com> wrote: > > Good morning, > >> Could anyone propose a better use case of CODESEPARATOR? > > Long ago, aj sent an email on Lightning-dev about use of CODESEPARATOR to > impose Scriptless Script even without Schnorr. It involved 3 signatures with > different CODESEPARATOR places, and forced R reuse so that the signatures to > claim the funds revealed the privkey. > > The script shown had all CODESEPARATOR in a single branch. > > I cannot claim to understand the script, and am having difficulty digging > through the mailinglist > > Regards, > ZmnSCPxj
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