otp.rb

#!/usr/bin/env ruby

print "MESSAGE> "
message = gets.gsub(/\s/, '').split(//)

print "PAD> "
pad = gets.gsub(/\s/, '').split(//)

message.zip(pad) do |mc, pc|
  puts "#{mc} | #{pc} | #{'%2i' % (nm = mc[0] - ?a)} | #{'%2i' % (np = pc[0] - ?a)} | #{'%2i' % ((nm + np) % 26)} | #{(((nm + np) % 26) + ?a).chr}"
end

cyphertext = message.zip(pad).collect do |m,p|
  (?a + (((m[0] - ?a) + (p[0] - ?a)) % 26)).chr
end

puts "CYPHERTEXT: #{cyphertext}"