Ohayou Hiroki-san,

I agree this possibility.

Of note is that this also helps support:

1. Cross-currency swaps without premium-free American Call Option.
   Exchanges will demand for a premium to be paid for revelation of the second 
preimage.
2. Non-custodial Escrow.
   The second preimage is shared between the escrow and the payer.

Both will also just as well be served by using points.

Regards,
ZmnSCPxj


>
> I explained Stuckless Payments on the basis of PTLCs before and some people 
> understood that this is a proposal that can be accomplished after PTLCs are 
> introduced. But this can also be accomplished using HTLC variants that are 
> not compatible with BOLT 1.x HTLCs. For simplicity, I'd like to describe them 
> in Miniscript policies (http://bitcoin.sipa.be/miniscript/).
>
> # The BOLT #3 offered HTLC policy
> or(pk(key_revocation),and(pk(key_remote),or(pk(key_local),hash160(H))))
> ->
> or(pk(key_revocation),and(pk(key_remote),or(pk(key_local),and(hash160(H),hash160(H)))))
>
> # The BOLT #3 received HTLC policy
> or(pk(key_revocation),and(pk(key_remote),or(and(pk(key_local),hash160(H)),older(1008))))
> ->
> or(pk(key_revocation),and(pk(key_remote),or(and(pk(key_local),and(hash160(H),hash160(H))),older(1008))))
>
> In both cases, I just changed `hash160(H)` to `and(hash160(H), hash160(H))`. 
> The notation seems to refer to the same `H`, but these are different. One is 
> provided by payer and the other is provided by payee. So we don't necessarily 
> have to wait for PTLCs.
>
> Regards,
> Hiroki
>
> 2019年6月27日(木) 18:45 Hiroki Gondo <[email protected]>:
>
> > Hi ZmnSCPxj and Bastien,
> >
> > When I was putting together this proposal, I thought it would be difficult 
> > for me to consider all the security and privacy issues. I am very glad that 
> > you raised the possible issues.
> >
> > > So my opinion, it is best to retain this property of "D does not know 
> > > payer A".
> >
> > I agree with your opinion too. I thought there was no problem if the ACK 
> > and the PoP were responses of the HTLCs and the key respectively. But,
> >
> > > The added communication round may allow intermediate node to guess the 
> > > payer.
> >
> > > With addition of new ACK-key turnaround, intermediate node can measure 
> > > time from send of ACK to receive of key, and guess its distance to payer.
> >
> > Right.
> >
> > > A can select another route (e.g. D -> E -> F -> A) and can create the ACK
> > > onion packet during the setup phase.
> > > A can then embed this ACK packet inside the last hop payload of the
> > > *add_htlc* onion packet.
> > > When D receives it, it simply sends that onion to the indicated recipient
> > > (E) which will unwrap and forward.
> > > This way D doesn't learn anything about A, and intermediate nodes aren't
> > > included in the ACK route so
> > > they don't learn anything either.
> >
> > I think this is likely to be an improvement. This could also be generalized 
> > as a case where a packet we send goes back to us via a given node. I need 
> > to understand more precisely the limitations of the onion packet including 
> > new specs under development. In the process, I will also consider 
> > combination of this proposal with AMP and new routing algorithms 
> > (Trampoline, Rendezvous).
> >
> > Regards,
> > Hiroki


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