code: public BigInteger getPositiveBigInteger() throws IOException {
          if (buffer.read() != DerValue.tag_Integer) {
              throw new IOException("DER input, Integer tag error");
          }
          return buffer.getBigInteger(getLength(buffer), true);
      }
docs: Returns an ASN.1 INTEGER value as a positive BigInteger.
  This is just to deal with implementations that incorrectly encode
  some values as negative.
  
  @return the integer held in this DER value as a BigInteger.