diff --git a/bin/main/ch/fhnw/kry/SPN.class b/bin/main/ch/fhnw/kry/SPN.class
index e5a110b..317df83 100644
Binary files a/bin/main/ch/fhnw/kry/SPN.class 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
index b5648b6..ec17f83 100644
Binary files a/bin/test/ch/fhnw/kry/SPNTest.class 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 d0f5e49..a4a31db 100644
--- a/src/main/java/ch/fhnw/kry/SPN.java
+++ b/src/main/java/ch/fhnw/kry/SPN.java
@@ -61,4 +61,14 @@ public class SPN {
         return x;
     }
 
+    public int swapBits(int x, int a, int b) {
+        int tmpA = (x & (0x1 << 15 - a)) == 0 ? 0 : 1;
+        int tmpB = (x & (0x1 << 15 - b)) == 0 ? 0 : 1;
+
+        x = tmpA == 0 ? (x & 0x1 << 15 - b) & 0b0 : (x & 0x1 << 15 - b) & ~0b0;
+
+
+        return 0;
+    }
+
 }
diff --git a/src/test/java/ch/fhnw/kry/SPNTest.java b/src/test/java/ch/fhnw/kry/SPNTest.java
index 3a29036..63952b1 100644
--- a/src/test/java/ch/fhnw/kry/SPNTest.java
+++ b/src/test/java/ch/fhnw/kry/SPNTest.java
@@ -33,4 +33,21 @@ class SPNTest {
 
         // System.out.print(Integer.toHexString(spn.substitution(x)));
     }
+
+    @Test
+    void swapBits() {
+        var spn = new SPN();
+
+        // given 
+        int x = 0xA;
+        int r = 0xC;
+
+        // when
+        int y = spn.swapBits(x, 1, 2);
+        int yy = spn.swapBits(x, 2, 1);
+
+        // then
+        assertEquals(r, y);
+        assertEquals(r, yy);
+    }
 }