Parameterize JubJub Python implementation, add parameters for a=-1 (equivalent to matter-inc curve)

[barryWhiteHat]

I also have to review the changes made by the matter team and make PR to https://github.com/barryWhiteHat/baby_jubjub

Do you have a reference for that?

[HarryR]

From: https://github.com/matterinc/sapling-crypto/blob/master/src/alt_babyjubjub/mod.rs#L5

• scaling = 1911982854305225074381251344103329931637610209014896889891168275855466657090
• a' = 21888242871839275222246405745257275088548364400416034343698204186575808495616 == -1 = a*scale^2 mod P
• d' = 12181644023421730124874158521699555681764249180949974110617291017600649128846 == -(168696/168700) = d*scale^2