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Просмотр файла: curve.js
"use strict";
Object.defineProperty(exports, "__esModule", { value: true });
exports.wNAF = wNAF;
exports.pippenger = pippenger;
exports.precomputeMSMUnsafe = precomputeMSMUnsafe;
exports.validateBasic = validateBasic;
/**
* Methods for elliptic curve multiplication by scalars.
* Contains wNAF, pippenger
* @module
*/
/*! noble-curves - MIT License (c) 2022 Paul Miller (paulmillr.com) */
const modular_js_1 = require("./modular.js");
const utils_js_1 = require("./utils.js");
const _0n = BigInt(0);
const _1n = BigInt(1);
function constTimeNegate(condition, item) {
const neg = item.negate();
return condition ? neg : item;
}
function validateW(W, bits) {
if (!Number.isSafeInteger(W) || W <= 0 || W > bits)
throw new Error('invalid window size, expected [1..' + bits + '], got W=' + W);
}
function calcWOpts(W, bits) {
validateW(W, bits);
const windows = Math.ceil(bits / W) + 1; // +1, because
const windowSize = 2 ** (W - 1); // -1 because we skip zero
return { windows, windowSize };
}
function validateMSMPoints(points, c) {
if (!Array.isArray(points))
throw new Error('array expected');
points.forEach((p, i) => {
if (!(p instanceof c))
throw new Error('invalid point at index ' + i);
});
}
function validateMSMScalars(scalars, field) {
if (!Array.isArray(scalars))
throw new Error('array of scalars expected');
scalars.forEach((s, i) => {
if (!field.isValid(s))
throw new Error('invalid scalar at index ' + i);
});
}
// Since points in different groups cannot be equal (different object constructor),
// we can have single place to store precomputes
const pointPrecomputes = new WeakMap();
const pointWindowSizes = new WeakMap(); // This allows use make points immutable (nothing changes inside)
function getW(P) {
return pointWindowSizes.get(P) || 1;
}
/**
* Elliptic curve multiplication of Point by scalar. Fragile.
* Scalars should always be less than curve order: this should be checked inside of a curve itself.
* Creates precomputation tables for fast multiplication:
* - private scalar is split by fixed size windows of W bits
* - every window point is collected from window's table & added to accumulator
* - since windows are different, same point inside tables won't be accessed more than once per calc
* - each multiplication is 'Math.ceil(CURVE_ORDER / 𝑊) + 1' point additions (fixed for any scalar)
* - +1 window is neccessary for wNAF
* - wNAF reduces table size: 2x less memory + 2x faster generation, but 10% slower multiplication
*
* @todo Research returning 2d JS array of windows, instead of a single window.
* This would allow windows to be in different memory locations
*/
function wNAF(c, bits) {
return {
constTimeNegate,
hasPrecomputes(elm) {
return getW(elm) !== 1;
},
// non-const time multiplication ladder
unsafeLadder(elm, n, p = c.ZERO) {
let d = elm;
while (n > _0n) {
if (n & _1n)
p = p.add(d);
d = d.double();
n >>= _1n;
}
return p;
},
/**
* Creates a wNAF precomputation window. Used for caching.
* Default window size is set by `utils.precompute()` and is equal to 8.
* Number of precomputed points depends on the curve size:
* 2^(𝑊−1) * (Math.ceil(𝑛 / 𝑊) + 1), where:
* - 𝑊 is the window size
* - 𝑛 is the bitlength of the curve order.
* For a 256-bit curve and window size 8, the number of precomputed points is 128 * 33 = 4224.
* @param elm Point instance
* @param W window size
* @returns precomputed point tables flattened to a single array
*/
precomputeWindow(elm, W) {
const { windows, windowSize } = calcWOpts(W, bits);
const points = [];
let p = elm;
let base = p;
for (let window = 0; window < windows; window++) {
base = p;
points.push(base);
// =1, because we skip zero
for (let i = 1; i < windowSize; i++) {
base = base.add(p);
points.push(base);
}
p = base.double();
}
return points;
},
/**
* Implements ec multiplication using precomputed tables and w-ary non-adjacent form.
* @param W window size
* @param precomputes precomputed tables
* @param n scalar (we don't check here, but should be less than curve order)
* @returns real and fake (for const-time) points
*/
wNAF(W, precomputes, n) {
// TODO: maybe check that scalar is less than group order? wNAF behavious is undefined otherwise
// But need to carefully remove other checks before wNAF. ORDER == bits here
const { windows, windowSize } = calcWOpts(W, bits);
let p = c.ZERO;
let f = c.BASE;
const mask = BigInt(2 ** W - 1); // Create mask with W ones: 0b1111 for W=4 etc.
const maxNumber = 2 ** W;
const shiftBy = BigInt(W);
for (let window = 0; window < windows; window++) {
const offset = window * windowSize;
// Extract W bits.
let wbits = Number(n & mask);
// Shift number by W bits.
n >>= shiftBy;
// If the bits are bigger than max size, we'll split those.
// +224 => 256 - 32
if (wbits > windowSize) {
wbits -= maxNumber;
n += _1n;
}
// This code was first written with assumption that 'f' and 'p' will never be infinity point:
// since each addition is multiplied by 2 ** W, it cannot cancel each other. However,
// there is negate now: it is possible that negated element from low value
// would be the same as high element, which will create carry into next window.
// It's not obvious how this can fail, but still worth investigating later.
// Check if we're onto Zero point.
// Add random point inside current window to f.
const offset1 = offset;
const offset2 = offset + Math.abs(wbits) - 1; // -1 because we skip zero
const cond1 = window % 2 !== 0;
const cond2 = wbits < 0;
if (wbits === 0) {
// The most important part for const-time getPublicKey
f = f.add(constTimeNegate(cond1, precomputes[offset1]));
}
else {
p = p.add(constTimeNegate(cond2, precomputes[offset2]));
}
}
// JIT-compiler should not eliminate f here, since it will later be used in normalizeZ()
// Even if the variable is still unused, there are some checks which will
// throw an exception, so compiler needs to prove they won't happen, which is hard.
// At this point there is a way to F be infinity-point even if p is not,
// which makes it less const-time: around 1 bigint multiply.
return { p, f };
},
/**
* Implements ec unsafe (non const-time) multiplication using precomputed tables and w-ary non-adjacent form.
* @param W window size
* @param precomputes precomputed tables
* @param n scalar (we don't check here, but should be less than curve order)
* @param acc accumulator point to add result of multiplication
* @returns point
*/
wNAFUnsafe(W, precomputes, n, acc = c.ZERO) {
const { windows, windowSize } = calcWOpts(W, bits);
const mask = BigInt(2 ** W - 1); // Create mask with W ones: 0b1111 for W=4 etc.
const maxNumber = 2 ** W;
const shiftBy = BigInt(W);
for (let window = 0; window < windows; window++) {
const offset = window * windowSize;
if (n === _0n)
break; // No need to go over empty scalar
// Extract W bits.
let wbits = Number(n & mask);
// Shift number by W bits.
n >>= shiftBy;
// If the bits are bigger than max size, we'll split those.
// +224 => 256 - 32
if (wbits > windowSize) {
wbits -= maxNumber;
n += _1n;
}
if (wbits === 0)
continue;
let curr = precomputes[offset + Math.abs(wbits) - 1]; // -1 because we skip zero
if (wbits < 0)
curr = curr.negate();
// NOTE: by re-using acc, we can save a lot of additions in case of MSM
acc = acc.add(curr);
}
return acc;
},
getPrecomputes(W, P, transform) {
// Calculate precomputes on a first run, reuse them after
let comp = pointPrecomputes.get(P);
if (!comp) {
comp = this.precomputeWindow(P, W);
if (W !== 1)
pointPrecomputes.set(P, transform(comp));
}
return comp;
},
wNAFCached(P, n, transform) {
const W = getW(P);
return this.wNAF(W, this.getPrecomputes(W, P, transform), n);
},
wNAFCachedUnsafe(P, n, transform, prev) {
const W = getW(P);
if (W === 1)
return this.unsafeLadder(P, n, prev); // For W=1 ladder is ~x2 faster
return this.wNAFUnsafe(W, this.getPrecomputes(W, P, transform), n, prev);
},
// We calculate precomputes for elliptic curve point multiplication
// using windowed method. This specifies window size and
// stores precomputed values. Usually only base point would be precomputed.
setWindowSize(P, W) {
validateW(W, bits);
pointWindowSizes.set(P, W);
pointPrecomputes.delete(P);
},
};
}
/**
* Pippenger algorithm for multi-scalar multiplication (MSM, 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 fieldN 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)
*/
function pippenger(c, fieldN, points, scalars) {
// 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
validateMSMPoints(points, c);
validateMSMScalars(scalars, fieldN);
if (points.length !== scalars.length)
throw new Error('arrays of points and scalars must have equal length');
const zero = c.ZERO;
const wbits = (0, utils_js_1.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(zero); // +1 for zero array
const lastBits = Math.floor((fieldN.BITS - 1) / windowSize) * windowSize;
let sum = zero;
for (let i = lastBits; i >= 0; i -= windowSize) {
buckets.fill(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 = 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 = 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;
}
/**
* Precomputed multi-scalar multiplication (MSM, Pa + Qb + Rc + ...).
* @param c Curve Point constructor
* @param fieldN field over CURVE.N - important that it's not over CURVE.P
* @param points array of L curve points
* @returns function which multiplies points with scaars
*/
function precomputeMSMUnsafe(c, fieldN, points, windowSize) {
/**
* Performance Analysis of Window-based Precomputation
*
* Base Case (256-bit scalar, 8-bit window):
* - Standard precomputation requires:
* - 31 additions per scalar × 256 scalars = 7,936 ops
* - Plus 255 summary additions = 8,191 total ops
* Note: Summary additions can be optimized via accumulator
*
* Chunked Precomputation Analysis:
* - Using 32 chunks requires:
* - 255 additions per chunk
* - 256 doublings
* - Total: (255 × 32) + 256 = 8,416 ops
*
* Memory Usage Comparison:
* Window Size | Standard Points | Chunked Points
* ------------|-----------------|---------------
* 4-bit | 520 | 15
* 8-bit | 4,224 | 255
* 10-bit | 13,824 | 1,023
* 16-bit | 557,056 | 65,535
*
* Key Advantages:
* 1. Enables larger window sizes due to reduced memory overhead
* 2. More efficient for smaller scalar counts:
* - 16 chunks: (16 × 255) + 256 = 4,336 ops
* - ~2x faster than standard 8,191 ops
*
* Limitations:
* - Not suitable for plain precomputes (requires 256 constant doublings)
* - Performance degrades with larger scalar counts:
* - Optimal for ~256 scalars
* - Less efficient for 4096+ scalars (Pippenger preferred)
*/
validateW(windowSize, fieldN.BITS);
validateMSMPoints(points, c);
const zero = c.ZERO;
const tableSize = 2 ** windowSize - 1; // table size (without zero)
const chunks = Math.ceil(fieldN.BITS / windowSize); // chunks of item
const MASK = BigInt((1 << windowSize) - 1);
const tables = points.map((p) => {
const res = [];
for (let i = 0, acc = p; i < tableSize; i++) {
res.push(acc);
acc = acc.add(p);
}
return res;
});
return (scalars) => {
validateMSMScalars(scalars, fieldN);
if (scalars.length > points.length)
throw new Error('array of scalars must be smaller than array of points');
let res = zero;
for (let i = 0; i < chunks; i++) {
// No need to double if accumulator is still zero.
if (res !== zero)
for (let j = 0; j < windowSize; j++)
res = res.double();
const shiftBy = BigInt(chunks * windowSize - (i + 1) * windowSize);
for (let j = 0; j < scalars.length; j++) {
const n = scalars[j];
const curr = Number((n >> shiftBy) & MASK);
if (!curr)
continue; // skip zero scalars chunks
res = res.add(tables[j][curr - 1]);
}
}
return res;
};
}
function validateBasic(curve) {
(0, modular_js_1.validateField)(curve.Fp);
(0, utils_js_1.validateObject)(curve, {
n: 'bigint',
h: 'bigint',
Gx: 'field',
Gy: 'field',
}, {
nBitLength: 'isSafeInteger',
nByteLength: 'isSafeInteger',
});
// Set defaults
return Object.freeze({
...(0, modular_js_1.nLength)(curve.n, curve.nBitLength),
...curve,
...{ p: curve.Fp.ORDER },
});
}
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