How to use the asn1.Ber.BitString function in asn1

if (g === false)
      return false;
    var y = readString(info.hostkey, info.hostkey._pos, self, callback);
    if (y === false)
      return false;

    asnWriter.startSequence();
    asnWriter.writeOID('1.2.840.10040.4.1');
    asnWriter.startSequence();
    asnWriter.writeBuffer(p, Ber.Integer);
    asnWriter.writeBuffer(q, Ber.Integer);
    asnWriter.writeBuffer(g, Ber.Integer);
    asnWriter.endSequence();
    asnWriter.endSequence();

    asnWriter.startSequence(Ber.BitString);
    asnWriter.writeByte(0x00);
    asnWriter.writeBuffer(y, Ber.Integer);
    asnWriter.endSequence();

    if (rawsig.length <= 40) {
      // change bare signature r and s values to ASN.1 DER values for OpenSSL
      var asnSigWriter = new Ber.Writer();
      asnSigWriter.startSequence();
      asnSigWriter.writeBuffer(rawsig.slice(0, 20), Ber.Integer);
      asnSigWriter.writeBuffer(rawsig.slice(20), Ber.Integer);
      asnSigWriter.endSequence();
      rawsig = asnSigWriter.buffer;
    }
  }
  asnWriter.endSequence();

function genOpenSSLECDSAPriv(oid, pub, priv) {
  var asnWriter = new Ber.Writer();
  asnWriter.startSequence();
    // version
    asnWriter.writeInt(0x01, Ber.Integer);
    // privateKey
    asnWriter.writeBuffer(priv, Ber.OctetString);
    // parameters (optional)
    asnWriter.startSequence(0xA0);
      asnWriter.writeOID(oid);
    asnWriter.endSequence();
    // publicKey (optional)
    asnWriter.startSequence(0xA1);
      asnWriter.startSequence(Ber.BitString);
        asnWriter.writeByte(0x00);
        // XXX: hack to write a raw buffer without a tag -- yuck
        asnWriter._ensure(pub.length);
        pub.copy(asnWriter._buf, asnWriter._offset, 0, pub.length);
        asnWriter._offset += pub.length;
        // end hack
      asnWriter.endSequence();
    asnWriter.endSequence();
  asnWriter.endSequence();
  return makePEM('EC PRIVATE', asnWriter.buffer);
}

var asnWriter = new Ber.Writer();
  asnWriter.startSequence();
    // algorithm
    asnWriter.startSequence();
      asnWriter.writeOID('1.2.840.10040.4.1'); // id-dsa
      // algorithm parameters
      asnWriter.startSequence();
        asnWriter.writeBuffer(p, Ber.Integer);
        asnWriter.writeBuffer(q, Ber.Integer);
        asnWriter.writeBuffer(g, Ber.Integer);
      asnWriter.endSequence();
    asnWriter.endSequence();

    // subjectPublicKey
    asnWriter.startSequence(Ber.BitString);
      asnWriter.writeByte(0x00);
      asnWriter.writeBuffer(y, Ber.Integer);
    asnWriter.endSequence();
  asnWriter.endSequence();
  return asnWriter.buffer;
}

} else {
    var p = Parser.readString(info.hostkey, info.hostkey._pos),
        q = Parser.readString(info.hostkey, info.hostkey._pos),
        g = Parser.readString(info.hostkey, info.hostkey._pos),
        y = Parser.readString(info.hostkey, info.hostkey._pos);

    asnWriter.startSequence();
    asnWriter.writeOID('1.2.840.10040.4.1');
    asnWriter.startSequence();
    asnWriter.writeBuffer(p, Ber.Integer);
    asnWriter.writeBuffer(q, Ber.Integer);
    asnWriter.writeBuffer(g, Ber.Integer);
    asnWriter.endSequence();
    asnWriter.endSequence();

    asnWriter.startSequence(Ber.BitString);
    asnWriter.writeByte(0x00);
    asnWriter.writeBuffer(y, Ber.Integer);
    asnWriter.endSequence();

    if (rawsig.length <= 40) {
      // change bare signature r and s values to ASN.1 DER values for OpenSSL
      var asnSigWriter = new Ber.Writer();
      asnSigWriter.startSequence();
      asnSigWriter.writeBuffer(rawsig.slice(0, 20), Ber.Integer);
      asnSigWriter.writeBuffer(rawsig.slice(20), Ber.Integer);
      asnSigWriter.endSequence();
      rawsig = asnSigWriter.buffer;
    }
  }
  asnWriter.endSequence();

function genOpenSSLEdPub(pub) {
  var asnWriter = new Ber.Writer();
  asnWriter.startSequence();
    // algorithm
    asnWriter.startSequence();
      asnWriter.writeOID('1.3.101.112'); // id-Ed25519
    asnWriter.endSequence();

    // PublicKey
    asnWriter.startSequence(Ber.BitString);
      asnWriter.writeByte(0x00);
      // XXX: hack to write a raw buffer without a tag -- yuck
      asnWriter._ensure(pub.length);
      pub.copy(asnWriter._buf, asnWriter._offset, 0, pub.length);
      asnWriter._offset += pub.length;
    asnWriter.endSequence();
  asnWriter.endSequence();
  return makePEM('PUBLIC', asnWriter.buffer);
}