Pedersen Hash done with tests

src/babyjub.js

@@ -0,0 +1,57 @@
+const bn128 = require("snarkjs").bn128;
+const bigInt = require("snarkjs").bigInt;
+
+exports.addPoint = addPoint;
+exports.mulPointEscalar = mulPointEscalar;
+exports.inCurve = inCurve;
+
+function addPoint(a,b) {
+    const q = bn128.r;
+    const cta = bigInt("168700");
+    const d = bigInt("168696");
+
+    const res = [];
+    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);
+    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.shr(1);
+    }
+
+    return res;
+}
+
+function isLowGrade(p) {
+    const r = bigInt("21888242871839275222246405745257275088614511777268538073601725287587578984328").shr(3);
+    const res= mulPointEscalar(p, r);
+    return (res[0].equals(bigInt(0))) && (res[1].equals(bigInt(1)));
+}
+
+function inCurve(p) {
+    const F = bn128.Fr;
+
+    const a = bigInt("168700");
+    const d = bigInt("168696");
+
+    const x2 = F.square(p[0]);
+    const y2 = F.square(p[1]);
+
+    if (!F.equals(
+        F.add(F.mul(a, x2), y2),
+        F.add(F.one, F.mul(F.mul(x2, y2), d)))) return false;
+
+    if (!isLowGrade(p)) return false;
+
+    return true;
+}