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

[ZmnSCPxj]

Good morning aj,

> 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).

Ah, yes, a generic zkp should work indeed.

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

Yes, the "existence-proof-of-a-proof-of-X is a proof-of-X".

Perhaps relevant? http://stevengoldfeder.com/papers/ZKCSP.pdf
Lightning payments are essentially zero-knowledge contingent payments already.

Regards,
ZmnSCPxj