[Lightning-dev] Proposal: Lightning Pre-Image Encryption Standard

Stepan Snigirev snigirev.stepan at gmail.com
Wed Jun 26 05:41:59 UTC 2019


Hi ZmnSCPxj,

> Does this require Bob to attempt both positive and negative sign for the
y-coordinate?
> Alternately we can force Sally to always use a scalar such that generated
point has a fixed sign (or some other property to derive the sign of the
missing coordinate).

The best would be if Sally uses the point with a fixed sign, then Bob
doesn't need to try twice and can start decrypting data from stream (for
example if it's a DRM key for a movie).
Similar approach is used for R-encoding in Schnorr signatures, so we could
use the same convention here.


On Tue, Jun 25, 2019 at 10:18 PM ZmnSCPxj <ZmnSCPxj at protonmail.com> wrote:

> Good morning Stepan, and Nadav,
>
> Both additions seem good idea to me.
>
> > - Sally generates the invoice with the preimage `S` (i.e. x-coordinate
> of this point to make it 32-bytes long)
>
> Does this require Bob to attempt both positive and negative sign for the
> y-coordinate?
> Alternately we can force Sally to always use a scalar such that generated
> point has a fixed sign (or some other property to derive the sign of the
> missing coordinate).
>
> Regards,
> ZmnSCPxj
>
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