#script from http://readlist.com/lists/ruby-lang.org/ruby-talk/11/55390.html

require "narray"

class String
def xor(other)
if other.empty?
self
else
s1 = self
s2 = other

if s1.length < s2.length
n, r = s2.length.divmod(s1.length)
s1 = s1 * n + s1[0, r]
elsif s2.length < s1.length
n, r = s1.length.divmod(s2.length)
s2 = s2 * n + s2[0, r]
end

a1 = NArray.to_na(s1, "byte")
a2 = NArray.to_na(s2, "byte")

(a1 ^ a2).to_s
end
end
end

hash = 'de9f2c7fd25e1b3afad3e85a0bd17d9b100db4b3'
a = hash[-19..-1];b = hash[0..19]
p a.xor(b) => "\\PXVP\a\x06Q\x00\vWT\x01RW\x03R\x03W\v"