@iden3/js-crypto/src/ff/scalar.ts

Crypto primitives for iden3

const hexLen = [0, 1, 2, 2, 3, 3, 3, 3, 4, 4, 4, 4, 4, 4, 4, 4];

export const fromString = (s: string, radix?: number): bigint => {
  if (!radix || radix === 10) {
    return BigInt(s);
  } else if (radix === 16) {
    if (s.slice(0, 2) == '0x') {
      return BigInt(s);
    } else {
      return BigInt('0x' + s);
    }
  }

  throw new Error('Unsupported radix');
};

export const e = fromString;

export const fromArray = (a: Uint8Array, r: number) => {
  let acc = BigInt(0);
  const radix = BigInt(r);
  for (let i = 0; i < a.length; i++) {
    acc = acc * radix + BigInt(a[i]);
  }
  return acc;
};

export const bitLength = (a: bigint): number => {
  const aS = a.toString(16);
  return (aS.length - 1) * 4 + hexLen[parseInt(aS[0], 16)];
};

export const isNegative = (a: bigint): boolean => {
  return BigInt(a) < BigInt(0);
};

export const isZero = (a: bigint) => {
  return a === zero;
};

export const shiftLeft = (a: bigint, n: bigint): bigint => {
  return a << n;
};

export const shiftRight = (a: bigint, n: bigint): bigint => {
  return a >> n;
};

export const shl = shiftLeft;
export const shr = shiftRight;

export const isOdd = (a: bigint): boolean => {
  return (a & one) == one;
};

export const naf = (n: bigint): number[] => {
  let E = n;
  const res = [];
  while (E) {
    if (E & one) {
      const z = 2 - Number(E % BigInt(4));
      res.push(z);
      E = E - BigInt(z);
    } else {
      res.push(0);
    }
    E = E >> one;
  }
  return res;
};

export const bits = (n: bigint): number[] => {
  let E = n;
  const res = [];
  while (E) {
    if (E & one) {
      res.push(1);
    } else {
      res.push(0);
    }
    E = E >> one;
  }
  return res;
};

export const toNumber = (s: bigint): number => {
  if (s > BigInt(Number.MAX_SAFE_INTEGER)) {
    throw new Error('Number too big');
  }
  return Number(s);
};

export const toArray = (s: bigint, r: bigint): number[] => {
  const res = [];
  let rem = s;
  const radix = r;
  while (rem) {
    res.unshift(Number(rem % radix));
    rem = rem / radix;
  }
  return res;
};

export const add = (a: bigint, b: bigint): bigint => {
  return a + b;
};

export const sub = (a: bigint, b: bigint): bigint => {
  return a - b;
};

export const neg = (a: bigint): bigint => {
  return -a;
};

export const mul = (a: bigint, b: bigint): bigint => {
  return a * b;
};

export const square = (a: bigint): bigint => {
  return a * a;
};

export const pow = (a: bigint, b: bigint): bigint => {
  return a ** b;
};

export const exp = (a: bigint, b: bigint): bigint => {
  return a ** b;
};

export const abs = (a: bigint): bigint => {
  return a >= 0 ? a : -a;
};

export const div = (a: bigint, b: bigint): bigint => {
  return a / b;
};

export const mod = (a: bigint, b: bigint): bigint => {
  return a % b;
};

export const eq = (a: bigint, b: bigint): boolean => {
  return a === b;
};

export const neq = (a: bigint, b: bigint): boolean => {
  return a !== b;
};

export const lt = (a: bigint, b: bigint): boolean => {
  return a < b;
};

export const gt = (a: bigint, b: bigint): boolean => {
  return a > b;
};

export const leq = (a: bigint, b: bigint): boolean => {
  return a <= b;
};

export const geq = (a: bigint, b: bigint): boolean => {
  return a >= b;
};

export const band = (a: bigint, b: bigint): bigint => {
  return a & b;
};

export const bor = (a: bigint, b: bigint): bigint => {
  return a | b;
};

export const bXor = (a: bigint, b: bigint): bigint => {
  return a ^ b;
};

export const land = (a: bigint, b: bigint): bigint => {
  return a && b;
};

export const lor = (a: bigint, b: bigint): bigint => {
  return a || b;
};

// Returns a buffer with Little Endian Representation
export const toRprLE = (buff: Uint8Array, o: number, e: bigint, n8: number): void => {
  const s = '0000000' + e.toString(16);
  const v = new Uint32Array(buff.buffer, buff.byteOffset + o, n8 / 4);
  const l = (((s.length - 7) * 4 - 1) >> 5) + 1; // Number of 32bit words;
  for (let i = 0; i < l; i++)
    v[i] = parseInt(s.substring(s.length - 8 * i - 8, s.length - 8 * i), 16);
  for (let i = l; i < v.length; i++) v[i] = 0;
  for (let i = v.length * 4; i < n8; i++)
    buff[i] = toNumber(band(shiftRight(e, BigInt(i * 8)), BigInt(0xff)));
};

// Returns a buffer with Big Endian Representation
export const toRprBE = (buff: Uint8Array, o: number, e: bigint, n8: number): void => {
  const s = '0000000' + e.toString(16);
  const v = new DataView(buff.buffer, buff.byteOffset + o, n8);
  const l = (((s.length - 7) * 4 - 1) >> 5) + 1; // Number of 32bit words;
  for (let i = 0; i < l; i++)
    v.setUint32(
      n8 - i * 4 - 4,
      parseInt(s.substring(s.length - 8 * i - 8, s.length - 8 * i), 16),
      false
    );

  // todo: check this
  for (let i = 0; i < n8 / 4 - l; i++) v.setInt32(0, 0, false);
};

// Passes a buffer with Little Endian Representation
export const fromRprLE = (buff: Uint8Array, o: number, n8?: number): bigint => {
  n8 = n8 || buff.byteLength;
  o = o || 0;
  const v = new Uint32Array(buff.buffer, buff.byteOffset + o, n8 / 4);
  const a = new Array(n8 / 4);
  v.forEach((ch, i) => (a[a.length - i - 1] = ch.toString(16).padStart(8, '0')));
  return fromString(a.join(''), 16);
};

// Passes a buffer with Big Endian Representation
export const fromRprBE = (buff: Uint8Array, o: number, n8: number): bigint => {
  n8 = n8 || buff.byteLength;
  o = o || 0;
  const v = new DataView(buff.buffer, buff.byteOffset + o, n8);
  const a = new Array(n8 / 4);
  for (let i = 0; i < n8 / 4; i++) {
    a[i] = v
      .getUint32(i * 4, false)
      .toString(16)
      .padStart(8, '0');
  }
  return fromString(a.join(''), 16);
};

export const toString = (a: bigint, radix = 10): string => {
  return a.toString(radix);
};

export const toLEBuff = (a: bigint): Uint8Array => {
  const buff = new Uint8Array(Math.floor((bitLength(a) - 1) / 8) + 1);
  toRprLE(buff, 0, a, buff.byteLength);
  return buff;
};

export const zero = BigInt(0);
export const one = BigInt(1);