diff --git a/src/main/java/ch/fhnw/kry/SPN.java b/src/main/java/ch/fhnw/kry/SPN.java
index 7d2e3c6..8c39bee 100644
--- a/src/main/java/ch/fhnw/kry/SPN.java
+++ b/src/main/java/ch/fhnw/kry/SPN.java
@@ -62,6 +62,9 @@ public class SPN {
         entry(15, 15)
     );
 
+    private static final int BLOCK_LENGTH = 16;
+    private static final int ROUNDS = 4;
+
     public String decrypt(int key, String chiffre) {
 
         return null;
@@ -78,11 +81,11 @@ public class SPN {
      * @return int array, with every int's lower 16 bits set to 16 bits of the input string.
      */
     public int[] strToArray(String bits) {
-        int[] data = new int[bits.length() / 16];
+        int[] data = new int[bits.length() / BLOCK_LENGTH];
 
         for (int i = 0; i < data.length; i++) {
-            int startIdx = i * 16;
-            String wordBits = bits.substring(startIdx, startIdx + 16);
+            int startIdx = i * BLOCK_LENGTH;
+            String wordBits = bits.substring(startIdx, startIdx + BLOCK_LENGTH);
             int word = Integer.parseInt(wordBits, 2);
             data[i] = word;
         }
@@ -100,14 +103,14 @@ public class SPN {
     public int encryptBlock(int key, int x) {
         x = init(key, x, 0); // initialer Weisschritt
 
-        for (int i = 1; i < 4; i++) { // for rounds > 0 && < r
+        for (int i = 1; i < ROUNDS; i++) { // for rounds > 0 && < r
             x = substitution(x, SBOX); // run through s-box
             x = permutation(x); // permutate
             x ^= k(key, i); // xor with derived round key
         }
 
         x = substitution(x, SBOX); // run through s-box
-        x ^= k(key, 4); // xor with last round key
+        x ^= k(key, ROUNDS); // xor with last round key
 
         return x;
     }
@@ -120,9 +123,9 @@ public class SPN {
      * @return Decrypted block.
      */
     public int decryptBlock(int key, int x) {
-        x = init(key, x, 4); // initialer Weisschritt
+        x = init(key, x, ROUNDS); // initialer Weisschritt
 
-        for (int i = 3; i > 0; i--) { // for rounds > 0 && < r, going in reverse
+        for (int i = ROUNDS - 1; i > 0; i--) { // for rounds > 0 && < r, going in reverse
             x = substitution(x, SBOX_REVERSE); // run through reverse s-box
             x = permutation(x); // permutate
             x ^= permutation(k(key, i)); // xor with permutated derived round key
@@ -144,7 +147,7 @@ public class SPN {
      * @return Derived key.
      */
     public int k(int key, int i) {
-        i *= 4;
+        i *= ROUNDS;
         int mask = 0xFFFF_0000 >>> i;
 
         return (key & mask) >>> ROUND_KEY_LENGTH - i;
@@ -174,7 +177,7 @@ public class SPN {
     public int permutation(int x) {
         Map<Integer, Boolean> blocked = new HashMap<>();
 
-        for (int i = 0; i < 16; i++) {
+        for (int i = 0; i < BLOCK_LENGTH; i++) {
             int target = PERMUTATION.get(i);
             if (!blocked.containsKey(target)) {
                 x = swapBits(x, i, target);