[Lightning-dev] Selling timestamps (via payment points and scalars + Pedersen commitments ) [try2]

[Lloyd Fournier]

This is a nice scheme.

Pedersen commitments + pay to point seems to be the most practical way to
do it but you can generalise this paying for a decommitment idea to any
commitment scheme. For example, you could do this in a payment channel with
hashes if we had something like OP_CAT. e.g HTLC unlocks based on whether
you can provide an r such that H(r || x) == C.

> Unfortunately that zkp already proves that C was generated based on x, so
you get your timestamp for free. Ooops. :(

I haven't studied zkp for circuits in general but I guess the
non-interactive proofs are fiat-shamir transformations of an interactive
protocol. Maybe you could just use the interactive zero knowledge protocol
which doesn't have the side effect of the verifier with a proof they can
give to others.

LL

On Thu, Sep 26, 2019 at 5:30 AM Anthony Towns <aj at erisian.com.au> wrote:

> On Wed, Sep 25, 2019 at 01:30:39PM +0000, ZmnSCPxj wrote:
> > > Since it's off chain, you could also provide R and C and a zero
> knowledge
> > > proof that you know an r such that:
> > > R = SHA256( r )
> > > C = SHA256( x || r )
>
> > > in which case you could do it with lightning as it exists today.
> > I can insist on paying only if the server reveals an `r` that matches
> some known `R` such that `R = SHA256(r)`, as currently in Lightning network.
> > However, how would I prove, knowing only `R` and `x`, and that there
> exists some `r` such that `R = SHA256(r)`, that `C = SHA256(x || r)`?
>
> If you know x and r, you can generate C and R and a zero knowledge proof
> of the relationship between x,C,R that doesn't reveal r (eg, I think
> you could do that with bulletproofs). Unfortunately that zkp already
> proves that C was generated based on x, so you get your timestamp for
> free. Ooops. :(
>
> Cheers,
> aj
>
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