circomlibjs/src/babyjub.js

140 lines
3.8 KiB
JavaScript
Raw Permalink Normal View History

2021-10-30 13:57:29 +02:00
import { getCurveFromName, Scalar } from "ffjavascript";
2021-10-06 11:28:14 +02:00
2021-10-30 13:57:29 +02:00
export default async function buildBabyJub() {
2021-11-23 13:22:47 +01:00
const bn128 = await getCurveFromName("bn128", true);
2021-10-30 13:57:29 +02:00
return new BabyJub(bn128.Fr);
}
2021-10-06 11:28:14 +02:00
2021-10-30 13:57:29 +02:00
class BabyJub {
constructor(F) {
this.F = F;
this.p = Scalar.fromString("21888242871839275222246405745257275088548364400416034343698204186575808495617");
this.pm1d2 = Scalar.div(Scalar.sub(this.p, Scalar.e(1)), Scalar.e(2));
this.Generator = [
F.e("995203441582195749578291179787384436505546430278305826713579947235728471134"),
F.e("5472060717959818805561601436314318772137091100104008585924551046643952123905")
];
this.Base8 = [
F.e("5299619240641551281634865583518297030282874472190772894086521144482721001553"),
F.e("16950150798460657717958625567821834550301663161624707787222815936182638968203")
];
this.order = Scalar.fromString("21888242871839275222246405745257275088614511777268538073601725287587578984328");
this.subOrder = Scalar.shiftRight(this.order, 3);
this.A = F.e("168700");
this.D = F.e("168696");
2021-10-06 11:28:14 +02:00
}
2021-10-30 13:57:29 +02:00
addPoint(a,b) {
const F = this.F;
2021-10-06 11:28:14 +02:00
2021-10-30 13:57:29 +02:00
const res = [];
2021-10-06 11:28:14 +02:00
2021-10-30 13:57:29 +02:00
/* does the equivalent of:
res[0] = bigInt((a[0]*b[1] + b[0]*a[1]) * bigInt(bigInt("1") + d*a[0]*b[0]*a[1]*b[1]).inverse(q)).affine(q);
res[1] = bigInt((a[1]*b[1] - cta*a[0]*b[0]) * bigInt(bigInt("1") - d*a[0]*b[0]*a[1]*b[1]).inverse(q)).affine(q);
*/
2021-10-06 11:28:14 +02:00
2021-10-30 13:57:29 +02:00
const beta = F.mul(a[0],b[1]);
const gamma = F.mul(a[1],b[0]);
const delta = F.mul(
F.sub(a[1], F.mul(this.A, a[0])),
F.add(b[0], b[1])
);
const tau = F.mul(beta, gamma);
const dtau = F.mul(this.D, tau);
2021-10-06 11:28:14 +02:00
2021-10-30 13:57:29 +02:00
res[0] = F.div(
F.add(beta, gamma),
F.add(F.one, dtau)
);
2021-10-06 11:28:14 +02:00
2021-10-30 13:57:29 +02:00
res[1] = F.div(
F.add(delta, F.sub(F.mul(this.A,beta), gamma)),
F.sub(F.one, dtau)
);
return res;
}
mulPointEscalar(base, e) {
const F = this.F;
let res = [F.e("0"),F.e("1")];
let rem = e;
let exp = base;
while (! Scalar.isZero(rem)) {
if (Scalar.isOdd(rem)) {
res = this.addPoint(res, exp);
}
exp = this.addPoint(exp, exp);
rem = Scalar.shiftRight(rem, 1);
}
return res;
2021-10-06 11:28:14 +02:00
}
2021-10-30 13:57:29 +02:00
inSubgroup(P) {
const F = this.F;
if (!this.inCurve(P)) return false;
const res= this.mulPointEscalar(P, this.subOrder);
return (F.isZero(res[0]) && F.eq(res[1], F.one));
2021-10-06 11:28:14 +02:00
}
2021-10-30 13:57:29 +02:00
inCurve(P) {
const F = this.F;
const x2 = F.square(P[0]);
const y2 = F.square(P[1]);
2021-10-06 11:28:14 +02:00
2021-10-30 13:57:29 +02:00
if (!F.eq(
F.add(F.mul(this.A, x2), y2),
F.add(F.one, F.mul(F.mul(x2, y2), this.D)))) return false;
2021-10-06 11:28:14 +02:00
2021-10-30 13:57:29 +02:00
return true;
}
packPoint(P) {
const F = this.F;
const buff = new Uint8Array(32);
F.toRprLE(buff, 0, P[1]);
const n = F.toObject(P[0]);
if (Scalar.gt(n, this.pm1d2)) {
buff[31] = buff[31] | 0x80;
}
return buff;
}
unpackPoint(buff) {
const F = this.F;
let sign = false;
const P = new Array(2);
if (buff[31] & 0x80) {
sign = true;
buff[31] = buff[31] & 0x7F;
}
P[1] = F.fromRprLE(buff, 0);
if (Scalar.gt(F.toObject(P[1]), this.p)) return null;
2021-10-06 11:28:14 +02:00
2021-10-30 13:57:29 +02:00
const y2 = F.square(P[1]);
2021-10-06 11:28:14 +02:00
2021-10-30 13:57:29 +02:00
const x2 = F.div(
F.sub(F.one, y2),
F.sub(this.A, F.mul(this.D, y2))
);
2021-10-06 11:28:14 +02:00
2021-10-30 13:57:29 +02:00
const x2h = F.exp(x2, F.half);
if (! F.eq(F.one, x2h)) return null;
let x = F.sqrt(x2);
if (x == null) return null;
if (sign) x = F.neg(x);
P[0] = x;
return P;
}
2021-10-06 11:28:14 +02:00
}