On Tue, Mar 07, 2017 at 02:18:53PM -0500, John Tromp wrote: > dear Andrew, > > >> Pieter Wuille in particular has stressed to me what a great feature of MW > >> it is > >> that everything looks the same, and that breaking this property should be > >> taken > >> very seriously. > > But with every kernel having both a fee and a locktime (which defaults > to the last confirmed block at the time of signing), things are pretty > uniform already. > > > He also suggested the locktime should be cancellable and extendable by > > having > > the would-be recipient reveal a key to the sender, but we didn't work out > > all > > the details. If this works then we should be able to get the effect of a > > relative lock-time, having indefinitely-open lightning channels, and so > > forth. > > Exciting times. > > > > Therefore I revise my proposal again, to remove the explicit locktime, and > > have only the fee. > > "I send the coins to a 3-of-3 multisig: my key, his key, and a third > key that I generate with some RSA timelock puzzle. Then I give him the > corresponding pubkey and SNARK-prove to him that the privkey is a > solution to the timelock puzzle." > > This seems like quite a bit of complexity. What extra security > assumptions are we relying on here? > I don't see the downside of simply requiring a locktime on every kernel... >
I was recently at Financial Crypto 2017 and I described Ethan's trick to about half a dozen people independently. Exactly zero of them were comfortable with it as the only way to do locktimes. The main complaint was that it required the RSA grinding. I argued reusability and outsourcing of the grinding, but people still felt that it was wasteful and likely to vary in speed from user to user. And of course, it's possible to do this even if the chain supports locktimes explicitly, so... I don't think I ever convinced Igno that we should have no kernel locktimes in grin, but I retract this opinion. The locktimes cost four extra bytes per kernel, are a very minor privacy hit, and give us a very simple mechanism for doing reliable locktimes whose timeout is agreed upon by all validators. Cheers Andrew -- Andrew Poelstra Mathematics Department, Blockstream Email: apoelstra at wpsoftware.net Web: https://www.wpsoftware.net/andrew "A goose alone, I suppose, can know the loneliness of geese who can never find their peace, whether north or south or west or east" --Joanna Newsom
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