indutny/elliptic

'use strict';

var BN = require('bn.js');

var utils = require('../utils');
var assert = utils.assert;

function Signature(options, enc) {
  if (options instanceof Signature)
    return options;

  if (this._importDER(options, enc))
    return;

  assert(options.r && options.s, 'Signature without r or s');
  this.r = new BN(options.r, 16);
  this.s = new BN(options.s, 16);
  if (options.recoveryParam === undefined)
    this.recoveryParam = null;
  else
    this.recoveryParam = options.recoveryParam;
}
module.exports = Signature;

function Position() {
  this.place = 0;
}

function getLength(buf, p) {
  var initial = buf[p.place++];
  if (!(initial & 0x80)) {
    return initial;
  }
  var octetLen = initial & 0xf;

  // Indefinite length or overflow
  if (octetLen === 0 || octetLen > 4) {
    return false;
  }

  var val = 0;
  for (var i = 0, off = p.place; i < octetLen; i++, off++) {
    val <<= 8;
    val |= buf[off];
    val >>>= 0;
  }

  // Leading zeroes
  if (val <= 0x7f) {
    return false;
  }

  p.place = off;
  return val;
}

function rmPadding(buf) {
  var i = 0;
  var len = buf.length - 1;
  while (!buf[i] && !(buf[i + 1] & 0x80) && i < len) {
    i++;
  }
  if (i === 0) {
    return buf;
  }
  return buf.slice(i);
}

Signature.prototype._importDER = function _importDER(data, enc) {
  data = utils.toArray(data, enc);
  var p = new Position();
  if (data[p.place++] !== 0x30) {
    return false;
  }
  var len = getLength(data, p);
  if (len === false) {
    return false;
  }
  if ((len + p.place) !== data.length) {
    return false;
  }
  if (data[p.place++] !== 0x02) {
    return false;
  }
  var rlen = getLength(data, p);
  if (rlen === false) {
    return false;
  }
  var r = data.slice(p.place, rlen + p.place);
  p.place += rlen;
  if (data[p.place++] !== 0x02) {
    return false;
  }
  var slen = getLength(data, p);
  if (slen === false) {
    return false;
  }
  if (data.length !== slen + p.place) {
    return false;
  }
  var s = data.slice(p.place, slen + p.place);
  if (r[0] === 0) {
    if (r[1] & 0x80) {
      r = r.slice(1);
    } else {
      // Leading zeroes
      return false;
    }
  }
  if (s[0] === 0) {
    if (s[1] & 0x80) {
      s = s.slice(1);
    } else {
      // Leading zeroes
      return false;
    }
  }

  this.r = new BN(r);
  this.s = new BN(s);
  this.recoveryParam = null;

  return true;
};

function constructLength(arr, len) {
  if (len < 0x80) {
    arr.push(len);
    return;
  }
  var octets = 1 + (Math.log(len) / Math.LN2 >>> 3);
  arr.push(octets | 0x80);
  while (--octets) {
    arr.push((len >>> (octets << 3)) & 0xff);
  }
  arr.push(len);
}

Signature.prototype.toDER = function toDER(enc) {
  var r = this.r.toArray();
  var s = this.s.toArray();

  // Pad values
  if (r[0] & 0x80)
    r = [ 0 ].concat(r);
  // Pad values
  if (s[0] & 0x80)
    s = [ 0 ].concat(s);

  r = rmPadding(r);
  s = rmPadding(s);

  while (!s[0] && !(s[1] & 0x80)) {
    s = s.slice(1);
  }
  var arr = [ 0x02 ];
  constructLength(arr, r.length);
  arr = arr.concat(r);
  arr.push(0x02);
  constructLength(arr, s.length);
  var backHalf = arr.concat(s);
  var res = [ 0x30 ];
  constructLength(res, backHalf.length);
  res = res.concat(backHalf);
  return utils.encode(res, enc);
};