[Lightning-dev] Selling Signatures: Another Reason to Move to Payment Points

[Lloyd Fournier]

Hi Nadav,

This is cool idea. I always imagined oracles would either give their DLC
signatures away for free or work via a subscription model.

The downside to this proposal is that the seller of the signature knows
which signature they're selling and therefore learns what kind of contract
the buyer must be involved in.

LL


On Thu, Jul 18, 2019 at 1:37 AM Nadav Kohen <nadav at suredbits.com> wrote:

> Hi All,
>
> I recently posted a proposal here for a scheme through which a trusted
> data provider can utilize the Lightning Network to privately sell data
> where data is received atomically with purchase.
>
> I've more recently been thinking about situations where a party, that is
> *not* trusted, is attempting to sell its signature to a known message. One
> example of a situation where this would be useful is if someone is trying
> to offer a DLC-like Option contract where they are essentially
> collateralizing themselves in a funding transaction and then selling their
> signatures to Contract Execution Transactions (CETs). In this example, we
> must ensure that the buyer of the signatures pays if and only if they
> receive valid signatures for the CETs which are known.
>
> I believe that this is achievable in a relatively straightforward way if
> we were to use ZmnSCPxj's proposed payment points with scalars (as opposed
> to payment hashes with pre-images). The (Schnorr) signature seller could
> give the buyer their one-time public key, `R = k*G`, through which the
> buyer could compute the payment point whose scalar is the seller's
> signature: `sig*G = R + h(m, R)*A` where `A` is the seller's public key.
> Using this value as the payment point, the buyer could be assured that they
> pay if and only if they receive `sig` from the seller, where `sig` is the
> desired valid signature of `m`!
>
> Best,
> Nadav
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