keys that are not 0 or r need to be permutated during encryption 🤦

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

@@ -88,7 +88,7 @@ public class SPN {
         for (int i = 3; i > 0; i--) {
             x = substitution(x, SBOX_REVERSE);
             x = permutation(x);
-            x ^= k(key, i);
+            x ^= permutation(k(key, i));
         }
 
         x = substitution(x, SBOX_REVERSE);

src/test/java/ch/fhnw/kry/SPNTest.java

@@ -63,7 +63,7 @@ class SPNTest {
     }
 
     @Test
-    void sp() {
+    void blockEncryptionDecryption() {
         var spn = new SPN();
 
         int x = 0x128F ;