js-moi-signer/src.ts/utils.ts

This package enables users to sign and verify messages in their applications.

const ZERO = new Uint8Array([0]);
const ErrRIsZero = "digest._r length cannot be zero";
const ErrSIsZero = "digest._s length cannot be zero";
const ErrRIsLong = "invalid digest._r length, should be 33 or 32"
const ErrSIsLong = "invalid digest._s length, should be 33 or 32"
const ErrSIsNegative = "digest._s value cannot be negative";
const ErrRIsNegative = "digest._r value cannot be negative";
const ErrRIsExcessPad = "digest._r value excessively padded";
const ErrSIsExcessPad = "digest._s value excessively padded";
const ErrDERExpected2 = "Expected DER integer (2)"

export type SigDigest = {
  _r: Uint8Array, 
  _s: Uint8Array
}

export function toDER(x: Uint8Array): Uint8Array {
  let i = 0;
  while (x[i] === 0) ++i;
  if (i === x.length) return ZERO;
  x = x.slice(i);
  if (x[0] & 0x80) {
    const result = new Uint8Array(1 + x.length);
    result.set(ZERO, 0);
    result.set(x, 1);
    return result;
  }
  return x;
}

export function fromDER(x: Uint8Array): Uint8Array {
  if (x[0] === 0x00) x = x.subarray(1);
  const uint8Array = new Uint8Array(32);
  const bstart = Math.max(0, 32 - x.length);
  uint8Array.set(x, bstart);

  return uint8Array;
}

// Reference https://github.com/bitcoin/bips/blob/master/bip-0066.mediawiki
// Format: 0x30 [total-length] 0x02 [R-length] [R] 0x02 [S-length] [S]
export function bip66Encode(rAndS: SigDigest): Uint8Array {
  let r = rAndS._r;
  let s = rAndS._s;

  let lenR = r.length;
  let lenS = s.length;
  if (lenR === 0) throw new Error(ErrRIsZero);
  if (lenS === 0) throw new Error(ErrSIsZero);
  if (lenR > 33) throw new Error(ErrRIsLong);
  if (lenS > 33) throw new Error(ErrSIsLong);
  if (r[0] & 0x80) throw new Error(ErrRIsNegative);
  if (s[0] & 0x80) throw new Error(ErrSIsNegative);
  if (lenR > 1 && (r[0] === 0x00) && !(r[1] & 0x80)) throw new Error(ErrRIsExcessPad);
  if (lenS > 1 && (s[0] === 0x00) && !(s[1] & 0x80)) throw new Error(ErrSIsExcessPad);

  let signature = new Uint8Array(6 + lenR + lenS);

  signature[0] = 0x30;
  signature[1] = signature.length - 2;
  signature[2] = 0x02;
  signature[3] = lenR;
  signature.set(r, 4);
  signature[4 + lenR] = 0x02;
  signature[5 + lenR] = lenS;
  signature.set(s, 6 + lenR);

  return signature;
}

export function bip66Decode(buffer: Uint8Array): SigDigest {
  if (buffer.length < 8) throw new Error('DER sequence length is too short');
  if (buffer.length > 72) throw new Error('DER sequence length is too long');
  if (buffer[0] !== 0x30) throw new Error('Expected DER sequence');
  if (buffer[1] !== buffer.length - 2) throw new Error('DER sequence length is invalid');
  if (buffer[2] !== 0x02) throw new Error('Expected DER integer');

  let lenR = buffer[3];
  if (lenR === 0) throw new Error(ErrRIsZero);
  if (5 + lenR >= buffer.length) throw new Error(ErrSIsLong);
  if (buffer[4 + lenR] !== 0x02) throw new Error(ErrDERExpected2);

  let lenS = buffer[5 + lenR];
  if (lenS === 0) throw new Error(ErrSIsZero);
  if (6 + lenR + lenS !== buffer.length) throw new Error(ErrSIsLong);

  if (buffer[4] & 0x80) throw new Error(ErrRIsNegative);
  if (lenR > 1 && (buffer[4] === 0x00) && !(buffer[5] & 0x80)) throw new Error(ErrRIsExcessPad);

  if (buffer[lenR + 6] & 0x80) throw new Error(ErrSIsNegative);
  if (lenS > 1 && (buffer[lenR + 6] === 0x00) && !(buffer[lenR + 7] & 0x80)) throw new Error(ErrSIsExcessPad);

  const digest: SigDigest = {
    _r: buffer.slice(4, 4 + lenR),
    _s: buffer.slice(6 + lenR)
  };

  return digest;
}

export function JoinSignature(digest: SigDigest): Uint8Array {
  const joinedArray = new Uint8Array(64);
  joinedArray.set(digest._r, 0);
  joinedArray.set(digest._s, 32);
  
  return joinedArray;
}