code: public void encode(byte tag, OutputStream out) throws IOException {
          out.write(tag);
          out.write(derEncoding, 1, derEncoding.length -1);
      }
docs: Put the DER encoding of this PKCS9 attribute set on an
  DerOutputStream, tagged with the given implicit tag.
  
  @param tag the implicit tag to use in the DER encoding.
  @param out the output stream on which to put the DER encoding.
  
  @exception IOException  on output error.