new tasks

Task/Caesar_cipher/Ruby/caesar_cipher.rb

@@ -0,0 +1,23 @@
+@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))}