diff --git a/bin/main/ch/fhnw/kry/SPN.class b/bin/main/ch/fhnw/kry/SPN.class
new file mode 100644
index 0000000..e5a110b
Binary files /dev/null and b/bin/main/ch/fhnw/kry/SPN.class differ
diff --git a/bin/test/ch/fhnw/kry/SPNTest.class b/bin/test/ch/fhnw/kry/SPNTest.class
new file mode 100644
index 0000000..b5648b6
Binary files /dev/null and b/bin/test/ch/fhnw/kry/SPNTest.class differ
diff --git a/src/main/java/ch/fhnw/kry/SPN.java b/src/main/java/ch/fhnw/kry/SPN.java
index 92de8d7..d0f5e49 100644
--- a/src/main/java/ch/fhnw/kry/SPN.java
+++ b/src/main/java/ch/fhnw/kry/SPN.java
@@ -1,7 +1,40 @@
 package ch.fhnw.kry;
 
+import java.util.Map;
+import java.util.HashMap;
+import static java.util.Map.entry;
+
 public class SPN {
     private final static int ROUND_KEY_LENGTH = 16;
+    private final Map<Integer, Integer> SBOX = Map.ofEntries(
+        entry(0xE, 0),
+        entry(4, 1),
+        entry(0xD, 2),
+        entry(1, 3),
+        entry(2, 4),
+        entry(0xF, 5),
+        entry(0xB, 6),
+        entry(8, 7),
+        entry(3, 8),
+        entry(0xA, 9),
+        entry(6, 0xA),
+        entry(0xC, 0xB),
+        entry(5, 0xC),
+        entry(9, 0xD),
+        entry(0, 0xE),
+        entry(7, 0xF)
+    );
+
+    public String decrypt(int key, String chiffre) {
+        
+        return null;
+    }
+
+    public int sp (int key, int x) {
+        x = init(key, x);
+
+        return x;
+    }
 
     public int k(int key, int i) {
         i *= 4;
@@ -9,4 +42,23 @@ public class SPN {
 
         return key & mask >>> ROUND_KEY_LENGTH - i;
     }
+
+    public int init(int key, int x) {
+        return x ^ k(key, 4);
+    } 
+
+    public int substitution(int x) {
+        int mask = 0xF000;
+        for (int i = 0; i < 4; i++) {
+            int j = 4 * i;
+            int key = (x & mask) >>> 12 - j;
+            int val = SBOX.get(key);
+            int replMask = ~(0xf << 12 - j); // Maske mit 4 0-Bits vorbereiten zur Vorbereitung vom Einfügen
+            x = x & replMask | (val << 12 - j); // x an der Stelle der 4 0-Bits mit val überschreiben
+
+            mask = mask >>> 4; // maske um 4 Bit für nächste Iteration verschieben
+        }
+        return x;
+    }
+
 }
diff --git a/src/test/java/ch/fhnw/kry/SPNTest.java b/src/test/java/ch/fhnw/kry/SPNTest.java
index 0f0d838..3a29036 100644
--- a/src/test/java/ch/fhnw/kry/SPNTest.java
+++ b/src/test/java/ch/fhnw/kry/SPNTest.java
@@ -15,4 +15,22 @@ class SPNTest {
         assertEquals(0xFFFF,  spn.k(key, 1));
         assertEquals(0xFFFF,  spn.k(key, 2));
     }
+
+    @Test
+    void substitution() {
+        var spn = new SPN();
+
+        //given
+        int x = 0xEF45;
+        int r = 0x051C;
+        System.out.print(Integer.toHexString(x));
+
+        //when
+        int y = spn.substitution(x);
+
+        // then
+        assertEquals(r, y);
+
+        // System.out.print(Integer.toHexString(spn.substitution(x)));
+    }
 }