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const bigInt = require("big-integer"); const ZqField = require("ffjavascript").ZqField; const utils = require("./utils.js");
exports.addPoint = addPoint; exports.mulPointEscalar = mulPointEscalar; exports.inCurve = inCurve; exports.inSubgroup = inSubgroup; exports.packPoint = packPoint; exports.unpackPoint = unpackPoint; exports.Generator = [ bigInt("995203441582195749578291179787384436505546430278305826713579947235728471134"), bigInt("5472060717959818805561601436314318772137091100104008585924551046643952123905") ]; exports.Base8 = [ bigInt("5299619240641551281634865583518297030282874472190772894086521144482721001553"), bigInt("16950150798460657717958625567821834550301663161624707787222815936182638968203") ]; exports.order = bigInt("21888242871839275222246405745257275088614511777268538073601725287587578984328"); exports.subOrder = exports.order.shiftRight(3); exports.p = bigInt("21888242871839275222246405745257275088548364400416034343698204186575808495617"); exports.A = bigInt("168700"); exports.D = bigInt("168696");
function addPoint(a,b) { const F = new ZqField(exports.p);
const res = [];
/* 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); */
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(exports.A, a[0])), F.add(b[0], b[1]) ); const tau = F.mul(beta, gamma); const dtau = F.mul(exports.D, tau);
res[0] = F.div( F.add(beta, gamma), F.add(bigInt.one, dtau) );
res[1] = F.div( F.add(delta, F.sub(F.mul(exports.A,beta), gamma)), F.sub(bigInt.one, dtau) );
return res; }
function mulPointEscalar(base, e) { let res = [bigInt("0"),bigInt("1")]; let rem = bigInt(e); let exp = base;
while (! rem.isZero()) { if (rem.isOdd()) { res = addPoint(res, exp); } exp = addPoint(exp, exp); rem = rem.shiftRight(1); }
return res; }
function inSubgroup(P) { if (!inCurve(P)) return false; const res= mulPointEscalar(P, exports.subOrder); return (res[0].equals(bigInt(0))) && (res[1].equals(bigInt(1))); }
function inCurve(P) { const F = new ZqField(exports.p);
const x2 = F.square(P[0]); const y2 = F.square(P[1]);
if (!F.eq( F.add(F.mul(exports.A, x2), y2), F.add(F.one, F.mul(F.mul(x2, y2), exports.D)))) return false;
return true; }
function packPoint(P) { const buff = utils.leInt2Buff(P[1], 32); if (P[0].greater(exports.p.shiftRight(1))) { buff[31] = buff[31] | 0x80; } return buff; }
function unpackPoint(_buff) { const F = new ZqField(exports.p);
const buff = Buffer.from(_buff); let sign = false; const P = new Array(2); if (buff[31] & 0x80) { sign = true; buff[31] = buff[31] & 0x7F; } P[1] = utils.leBuff2int(buff); if (P[1].greaterOrEquals(exports.p)) return null;
const y2 = F.square(P[1]);
let x = F.sqrt(F.div( F.sub(F.one, y2), F.sub(exports.A, F.mul(exports.D, y2))));
if (x == null) return null;
if (sign) x = F.neg(x);
P[0] = x;
return P; }
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