start with the K function

src/main/java/ch/fhnw/kry/Main.java

@@ -5,6 +5,9 @@ package ch.fhnw.kry;
  */
 public class Main {
 
+    private static final String KEY = "00111010100101001101011000111111";
+    private static final String CHIFFRE = "00000100110100100000101110111000000000101000111110001110011111110110000001010001010000111010000000010011011001110010101110110000";
+
     public static void main(String[] args)  {
 
     }

src/main/java/ch/fhnw/kry/SPN.java

@@ -0,0 +1,10 @@
+package ch.fhnw.kry;
+
+public class SPN {
+    public int k(int key, int i) {
+        i *= 4;
+        int mask = 0xFFFF >>> i;
+
+        return key & mask;
+    }
+}