code: public BigInteger getPositiveBigInteger() throws IOException {
          if (tag != tag_Integer)
              throw new IOException("DerValue.getBigInteger, not an int " + tag);
          return buffer.getBigInteger(data.available(), 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.