# File lib/openid/util.rb, line 169
    def Util.strxor(s1, s2)
      raise ArgumentError if s1.length != s2.length
      length = [s1.length, s2.length].min - 1
      a = (0..length).collect {|i| (s1[i]^s2[i]).chr}
      a.join("")
    end