sub bigint_to_bytearray {
   my $bigint = shift;
   die "Negative numbers not supported" if $bigint < 0;

   my @bytes = unpack('c*', pack('H*', substr($bigint->as_hex, 2)));
   unshift @bytes, 0x00 if $bytes[0] < 0;  # Add sign bit if necessary
   return @bytes;
}