def to_hex(sep_bytes=false)
    hx = @bytes.unpack('H*')[0].upcase
    if sep_bytes
      sep = ""
      (0...hx.size).step(2) do |i|
        sep << " " unless i==0
        sep << hx[i,2]
      end
      hx = sep
    end
    hx
  end
def to_hex(sep_bytes=false)
    hx = @bytes.unpack('H*')[0].upcase
    if sep_bytes
      sep = ""
      (0...hx.size).step(2) do |i|
        sep << " " unless i==0
        sep << hx[i,2]
      end
      hx = sep
    end
    hx
  end
return an hex representation of a byte string