Add MSM

src/abstract/curve.ts

@@ -1,7 +1,7 @@
 /*! noble-curves - MIT License (c) 2022 Paul Miller (paulmillr.com) */
 // Abelian group utilities
 import { IField, validateField, nLength } from './modular.js';
-import { validateObject } from './utils.js';
+import { validateObject, bitLen } from './utils.js';
 const _0n = BigInt(0);
 const _1n = BigInt(1);
 
@@ -181,6 +181,62 @@ export function wNAF<T extends Group<T>>(c: GroupConstructor<T>, bits: number) {
   };
 }
 
+/**
+ * Pippenger algorithm for multi-scalar multiplication (MSM).
+ * MSM is basically (Pa + Qb + Rc + ...).
+ * 30x faster vs naive addition on L=4096, 10x faster with precomputes.
+ * For N=254bit, L=1, it does: 1024 ADD + 254 DBL. For L=5: 1536 ADD + 254 DBL.
+ * Algorithmically constant-time (for same L), even when 1 point + scalar, or when scalar = 0.
+ * @param c Curve Point constructor
+ * @param field field over CURVE.N - important that it's not over CURVE.P
+ * @param points array of L curve points
+ * @param scalars array of L scalars (aka private keys / bigints)
+ */
+export function pippenger<T extends Group<T>>(
+  c: GroupConstructor<T>,
+  field: IField<bigint>,
+  points: T[],
+  scalars: bigint[]
+): T {
+  // If we split scalars by some window (let's say 8 bits), every chunk will only
+  // take 256 buckets even if there are 4096 scalars, also re-uses double.
+  // TODO:
+  // - https://eprint.iacr.org/2024/750.pdf
+  // - https://tches.iacr.org/index.php/TCHES/article/view/10287
+  // 0 is accepted in scalars
+  if (!Array.isArray(points) || !Array.isArray(scalars) || scalars.length !== points.length)
+    throw new Error('arrays of scalars and points must have equal length');
+  scalars.forEach((s, i) => {
+    if (!field.isValid(s)) throw new Error(`wrong scalar at index ${i}`);
+  });
+  points.forEach((p, i) => {
+    if (!(p instanceof (c as any))) throw new Error(`wrong point at index ${i}`);
+  });
+  const wbits = bitLen(BigInt(points.length));
+  const windowSize = wbits > 12 ? wbits - 3 : wbits > 4 ? wbits - 2 : wbits ? 2 : 1; // in bits
+  const MASK = (1 << windowSize) - 1;
+  const buckets = new Array(MASK + 1).fill(c.ZERO); // +1 for zero array
+  const lastBits = Math.floor((field.BITS - 1) / windowSize) * windowSize;
+  let sum = c.ZERO;
+  for (let i = lastBits; i >= 0; i -= windowSize) {
+    buckets.fill(c.ZERO);
+    for (let j = 0; j < scalars.length; j++) {
+      const scalar = scalars[j];
+      const wbits = Number((scalar >> BigInt(i)) & BigInt(MASK));
+      buckets[wbits] = buckets[wbits].add(points[j]);
+    }
+    let resI = c.ZERO; // not using this will do small speed-up, but will lose ct
+    // Skip first bucket, because it is zero
+    for (let j = buckets.length - 1, sumI = c.ZERO; j > 0; j--) {
+      sumI = sumI.add(buckets[j]);
+      resI = resI.add(sumI);
+    }
+    sum = sum.add(resI);
+    if (i !== 0) for (let j = 0; j < windowSize; j++) sum = sum.double();
+  }
+  return sum as T;
+}
+
 // Generic BasicCurve interface: works even for polynomial fields (BLS): P, n, h would be ok.
 // Though generator can be different (Fp2 / Fp6 for BLS).
 export type BasicCurve<T> = {

src/abstract/edwards.ts

@@ -1,7 +1,15 @@
 /*! noble-curves - MIT License (c) 2022 Paul Miller (paulmillr.com) */
 // Twisted Edwards curve. The formula is: ax² + y² = 1 + dx²y²
-import { AffinePoint, BasicCurve, Group, GroupConstructor, validateBasic, wNAF } from './curve.js';
-import { mod } from './modular.js';
+import {
+  AffinePoint,
+  BasicCurve,
+  Group,
+  GroupConstructor,
+  validateBasic,
+  wNAF,
+  pippenger,
+} from './curve.js';
+import { mod, Field } from './modular.js';
 import * as ut from './utils.js';
 import { ensureBytes, FHash, Hex, memoized, abool } from './utils.js';
 
@@ -70,6 +78,7 @@ export interface ExtPointConstructor extends GroupConstructor<ExtPointType> {
   fromAffine(p: AffinePoint<bigint>): ExtPointType;
   fromHex(hex: Hex): ExtPointType;
   fromPrivateKey(privateKey: Hex): ExtPointType;
+  msm(points: ExtPointType[], scalars: bigint[]): ExtPointType;
 }
 
 /**
@@ -218,6 +227,10 @@ export function twistedEdwards(curveDef: CurveType): CurveFn {
       const toInv = Fp.invertBatch(points.map((p) => p.ez));
       return points.map((p, i) => p.toAffine(toInv[i])).map(Point.fromAffine);
     }
+    // Multiscalar Multiplication
+    static msm(points: Point[], scalars: bigint[]) {
+      return pippenger(Point, Fn, points, scalars);
+    }
 
     // "Private method", don't use it directly
     _setWindowSize(windowSize: number) {
@@ -419,6 +432,7 @@ export function twistedEdwards(curveDef: CurveType): CurveFn {
   }
   const { BASE: G, ZERO: I } = Point;
   const wnaf = wNAF(Point, nByteLength * 8);
+  const Fn = Field(CURVE.n, CURVE.nBitLength);
 
   function modN(a: bigint) {
     return mod(a, CURVE_ORDER);

src/abstract/weierstrass.ts

@@ -1,6 +1,14 @@
 /*! noble-curves - MIT License (c) 2022 Paul Miller (paulmillr.com) */
 // Short Weierstrass curve. The formula is: y² = x³ + ax + b
-import { AffinePoint, BasicCurve, Group, GroupConstructor, validateBasic, wNAF } from './curve.js';
+import {
+  AffinePoint,
+  BasicCurve,
+  Group,
+  GroupConstructor,
+  validateBasic,
+  wNAF,
+  pippenger,
+} from './curve.js';
 import * as mod from './modular.js';
 import * as ut from './utils.js';
 import { CHash, Hex, PrivKey, ensureBytes, memoized, abool } from './utils.js';
@@ -85,6 +93,7 @@ export interface ProjConstructor<T> extends GroupConstructor<ProjPointType<T>> {
   fromHex(hex: Hex): ProjPointType<T>;
   fromPrivateKey(privateKey: PrivKey): ProjPointType<T>;
   normalizeZ(points: ProjPointType<T>[]): ProjPointType<T>[];
+  msm(points: ProjPointType<T>[], scalars: bigint[]): ProjPointType<T>;
 }
 
 export type CurvePointsType<T> = BasicWCurve<T> & {
@@ -412,6 +421,11 @@ export function weierstrassPoints<T>(opts: CurvePointsType<T>): CurvePointsRes<T
       return Point.BASE.multiply(normPrivateKeyToScalar(privateKey));
     }
 
+    // Multiscalar Multiplication
+    static msm(points: Point[], scalars: bigint[]) {
+      return pippenger(Point, Fn, points, scalars);
+    }
+
     // "Private method", don't use it directly
     _setWindowSize(windowSize: number) {
       wnaf.setWindowSize(this, windowSize);
@@ -665,6 +679,7 @@ export function weierstrassPoints<T>(opts: CurvePointsType<T>): CurvePointsRes<T
   }
   const _bits = CURVE.nBitLength;
   const wnaf = wNAF(Point, CURVE.endo ? Math.ceil(_bits / 2) : _bits);
+  const Fn = mod.Field(CURVE.n, _bits); // TODO: export/re-use maybe?
   // Validate if generator point is on curve
   return {
     CURVE,

test/basic.test.js

@@ -468,6 +468,33 @@ for (const name in CURVES) {
             { numRuns: NUM_RUNS }
           )
         );
+        should('MSM (basic)', () => {
+          equal(p.msm([p.BASE], [0n]), p.ZERO, '0*G');
+          equal(p.msm([], []), p.ZERO, 'empty');
+          equal(p.msm([p.ZERO], [123n]), p.ZERO, '123 * Infinity');
+          equal(p.msm([p.BASE], [123n]), p.BASE.multiply(123n), '123 * G');
+          const points = [p.BASE, p.BASE.multiply(2n), p.BASE.multiply(4n), p.BASE.multiply(8n)];
+          // 1*3 + 5*2 + 4*7 + 11*8 = 129
+          equal(p.msm(points, [3n, 5n, 7n, 11n]), p.BASE.multiply(129n), '129 * G');
+        });
+        should('MSM (rand)', () =>
+          fc.assert(
+            fc.property(fc.array(fc.tuple(FC_BIGINT, FC_BIGINT)), FC_BIGINT, (pairs) => {
+              let total = 0n;
+              const scalars = [];
+              const points = [];
+              for (const [ps, s] of pairs) {
+                points.push(p.BASE.multiply(ps));
+                scalars.push(s);
+                total += ps * s;
+              }
+              total = mod.mod(total, CURVE_ORDER);
+              const exp = total ? p.BASE.multiply(total) : p.ZERO;
+              equal(p.msm(points, scalars), exp, 'total');
+            }),
+            { numRuns: NUM_RUNS }
+          )
+        );
       });
 
       for (const op of ['add', 'subtract']) {