push garbage

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

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+package ch.fhnw.kry;
+
+import java.util.Random;
+import java.util.concurrent.ThreadLocalRandom;
+
+public class CTR {
+    private final SPN spn = new SPN();
+    private final int iv;
+    private final int key;
+
+    public CTR(int key) {
+        this.iv = generateIV();
+        this.key = key;
+    }
+
+    public int getIV() {
+        return iv;
+    }
+
+    public int generateIV() {
+        Random random = ThreadLocalRandom.current();
+        byte[] r = new byte[2];
+        random.nextBytes(r);
+
+        return r[0] << 8 & r[1];
+    }
+
+    public int decrypt(int block, int idx) {
+        int e = (iv + idx) % (1 << 16);
+        e = spn.decryptBlock(key, e);
+
+        return block ^ e;
+    }
+}