added encryption algorithm

src/encrypt.lua

@@ -85,4 +85,17 @@ for f = 1, 3 * math.max(t,c) do
 	]]
 end
 
-
+--encrypt
+--assume that the input block is given in two w-bit registers 
+--A and B
+--the A and B found in the setup have been loaded into the S
+--array and can now be filled with words of plaintext
+A = A + S[1]
+B = B + S[2]
+for i = 1, r do
+	A = bit.rol((bit.bxor(A, B)), B) + S[2*i]
+	B = bit.rol((bit.bxor(B, A)), A) + S[2*i + 1]
+end
+print("Encrypted output A & B")
+print(A)
+print(B)