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From: Rusty Russell <rusty@rustcorp.com.au>
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Subject: Re: [bitcoin-dev] Safer sighashes and more granular SIGHASH_NOINPUT
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Johnson Lau <jl2012@xbt.hk> writes:
> I don=E2=80=99t think this has been mentioned: without signing the script=
or masked script, OP_CODESEPARATOR becomes unusable or insecure with NOINP=
UT.
>
> In the new sighash proposal, we will sign the hash of the full script (or=
masked script), without any truncation. To make OP_CODESEPARATOR works lik=
e before, we will commit to the position of the last executed OP_CODESEPARA=
TOR. If NOINPUT doesn=E2=80=99t commit to the masked script, it will just b=
lindly committing to a random OP_CODESEPARATOR position, which a wallet cou=
ldn=E2=80=99t know what codes are actually being executed.
My anti-complexity argument leads me to ask why we'd support
OP_CODESEPARATOR at all? Though my argument is weaker here: no wallet
need support it.
But I don't see how OP_CODESEPARATOR changes anything here, wrt NOINPUT?
Remember, anyone can create an output which can be spent by any NOINPUT,
whether we go for OP_MASK or simply not commiting to the input script.
Confused,
Rusty.
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