Add a function to decrypt a message with the gamma cipher.

src/cipher_analytical_machine/ciphers/gamma.clj

@@ -65,3 +65,14 @@
          (map vector array)
          (map (fn [[a g]] (add-mod a g module))))))
 
+(defn decrypt-message
+  "Decrypt a message using the gamma cipher. The function is case-insensitive. The key is an array of three elements [a b c]. The array contains integer in range [0, module)."
+  [key symbols message]
+  (let [module (count symbols)
+        table (ss/generate-sorted-substitution-table symbols)]
+    (->> message
+         (ss/decrypt-by-table (set/map-invert table))
+         (decrypt-array key module)
+         (ss/decrypt-by-table table)
+         (cs/join))))
+