new files

Task/Caesar-cipher/Ruby/caesar-cipher.rb

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+@atoz = Hash.new do |hash, key|
+  str = ('A'..'Z').to_a.rotate(key).join("")
+  hash[key] = (str << str.downcase)
+end
+
+def encrypt(key, plaintext)
+  (1..25) === key or raise ArgumentError, "key not in 1..25"
+  plaintext.tr(@atoz[0], @atoz[key])
+end
+
+def decrypt(key, ciphertext)
+  (1..25) === key or raise ArgumentError, "key not in 1..25"
+  ciphertext.tr(@atoz[key], @atoz[0])
+end
+
+original = "THEYBROKEOURCIPHEREVERYONECANREADTHIS"
+en = encrypt(3, original)
+de = decrypt(3, en)
+
+[original, en, de].each {|e| puts e}
+
+puts 'OK' if
+  (1..25).all? {|k| original == decrypt(k, encrypt(k, original))}