: hexdigest

    ޤǤɲäʸФϥåͤASCIIɤȤä
    16ʿ򼨤 'fe5c2235f48d2bcc911afabea23cd5aa' 
    褦32ʸʸ˥󥳡ɤ֤Rubyǽ񤯤ȰʲƱ

        def hexdigest
          ret = ''
          digest.each_byte {|i| ret << sprintf('%02x', i) }
          ret
        end

