I am new to Ruby and I could use some expert advice as to how I can
make this code run faster.

def scramble(fname)
    f = File.new(fname, "rb")
    _fname = fname + ".scrambled"
    begin
        File.exist?(_fname) if File.delete(_fname)
    rescue
    end
    ff = File.new(_fname, "wb+")
    for l in f
        l.each_byte{|c| ff.write((c | 0x80).chr) }
    end
    f.close()
    ff.close()
end