diff --git a/Credentials.java b/Credentials.java
new file mode 100644
index 0000000..482bf9a
--- /dev/null
+++ b/Credentials.java
@@ -0,0 +1,116 @@
+import java.util.Scanner;
+
+public class Credentials {
+    private String login;
+    private String password;
+    private static Scanner s = new Scanner(System.in);
+
+    /*public Credentials(String login, String password) {
+        this.login = login;
+        this.password = password;
+    }*/
+
+    public static void main(String[] args) {
+        if (login()) {
+            register();
+        }
+        boolean valid = false;
+        //Scanner s = new Scanner(System.in);
+        for (int i = 0; i < 3; i++) {
+            System.out.print("Benutzername: ");
+            String login = s.next();
+            System.out.print("Passwort: ");
+            String pwd = s.next();
+            if (valid(login, pwd)) {
+                System.out.println("Hello World");
+                valid = true;
+            }
+            if(valid) {
+                i = 3;
+            } else {
+                System.out.println("Der Benutzername oder das Passwort ist falsch. Übrige Versuche: " + (2 - i));
+            }
+        }
+        s.close();
+        if (!valid) {
+            System.out.println("Sie sind gesperrt.");
+        }
+    }
+
+    public static boolean valid(String login, String password) {
+        String[] data = Helpers.readTextdatei("passwd");
+        for (int i = 0; i < data.length; i++) {
+            if (data[i].equals(login)) {
+                if (Helpers.getHash(password).equals(data[i + 1])) {
+                    return true;
+                } else {
+                    return false;
+                }
+            }
+        }
+        return false;
+    }
+
+    public static boolean login() {
+        //Scanner s2 = new Scanner(System.in);
+        System.out.print("Tippen Sie '0', um sich zu registrieren; Tippen Sie '1', um sich anzumelden: ");
+        String answer = s.next();
+        //s2.close();
+        if (answer.equals("0")) {
+            return true;
+        } else {
+            return false;
+        }
+    }
+
+    public static void register() {
+        //Scanner s3 = new Scanner(System.in);
+        System.out.print("Ihr Benutzername: ");
+        String user = s.next();
+        if (checkUser(user)) {
+            System.out.print("Ihr Passwort: ");
+            String pwd1 = s.next();
+            System.out.print("Passwort erneut eingeben: ");
+            String pwd2 = s.next();
+            if(pwd1.equals(pwd2)) {
+                if(checkPassword(pwd1)) {
+                    String[] data = Helpers.readTextdatei("passwd");
+                    pwd1 = Helpers.getHash(pwd1);
+                    String[] lines = new String[data.length + 2];
+                    for (int i = 0; i < data.length; i++) {
+                        lines[i] = data[i];
+                    }
+                    lines[data.length] = user;
+                    lines[data.length + 1] = pwd1;
+                    Helpers.writeTextdatei("passwd", lines);
+                    System.out.println("Der Benutzer wurde erfolgreich hinzugefügt. Sie können sich nun anmelden:");
+                } else {
+                    System.out.println("Das Passwort entspricht nicht den Sicherheitsvorgaben.");
+                }
+            } else {
+                System.out.println("Die Passwörter stimmen nicht überein.");
+            }
+        } else {
+            System.out.println("Dieser Benutzername ist bereits vergeben.");
+        }
+        //s3.close();
+    }
+
+    public static boolean checkUser(String user) {
+        String[] data = Helpers.readTextdatei("passwd");
+        for (int i = 0; i < data.length; i++) {
+            if (user.equals(data[i])) {
+                return false;
+            }
+            i++;
+        }
+        return true;
+    }
+
+    public static boolean checkPassword(String pwd) {
+        if (pwd.length() < 8) {
+            return false;
+        }
+        return true;
+    }
+}
diff --git a/CredentialsTest.java b/CredentialsTest.java
new file mode 100644
index 0000000..71d244d
--- /dev/null
+++ b/CredentialsTest.java
@@ -0,0 +1,46 @@
+import org.junit.jupiter.api.Test;
+
+import static org.junit.jupiter.api.Assertions.*;
+
+class CredentialsTest {
+
+    Credentials credentials = new Credentials();
+
+    @Test
+    void valid() {
+        //Credentials credentials = new Credentials();
+        assertTrue(credentials.valid("hofmannol", "GERONIMO"));
+        assertTrue(credentials.valid("wimmerma", "GEHEIM123"));
+        assertFalse(credentials.valid("meierandr", "GERONIMO"));
+        assertFalse(credentials.valid("wimmerma", "ÖFFENTLICH123"));
+    }
+
+    @Test
+    void login() {
+        //Credentials credentials = new Credentials();
+
+    }
+
+    @Test
+    void register() {
+        //Credentials credentials = new Credentials();
+
+    }
+
+    @Test
+    void checkUser() {
+        assertTrue(credentials.checkUser("heinz"));
+        assertTrue(credentials.checkUser("hoffmannol"));
+        assertFalse(credentials.checkUser("hofmannol"));
+
+        //Credentials credentials = new Credentials();
+    }
+
+    @Test
+    void checkPassword() {
+        //Credentials credentials = new Credentials();
+        assertTrue(credentials.checkPassword("12345678"));
+        assertTrue(credentials.checkPassword("GERONIMO"));
+        assertFalse(credentials.checkPassword("D1234"));
+    }
+}
\ No newline at end of file
diff --git a/Helpers.java b/Helpers.java
new file mode 100644
index 0000000..ec49cf0
--- /dev/null
+++ b/Helpers.java
@@ -0,0 +1,55 @@
+import java.io.*;
+import java.math.BigInteger;
+import java.security.MessageDigest;
+import java.security.NoSuchAlgorithmException;
+import java.util.ArrayList;
+
+public class Helpers {
+
+    // Lesen einer Textdatei in ein Stringarray
+    public static String[] readTextdatei(String name) {
+        String line;
+        ArrayList<String> result = new ArrayList<String>();
+        try {
+            FileReader fr = new FileReader(name);
+            BufferedReader br = new BufferedReader(fr);
+            while ((line = br.readLine()) != null)
+                result.add(line);
+            br.close();
+        }
+        catch (IOException e) {
+            e.printStackTrace();
+        }
+        return result.toArray(new String[]{});
+    }
+
+    // Schreiben eines Stringarray in eine Textdatei
+    public static void writeTextdatei(String name, String[] lines) {
+        try {
+            FileWriter fw = new FileWriter(name);
+            BufferedWriter bw = new BufferedWriter(fw);
+            PrintWriter pw = new PrintWriter(bw);
+            for (int i = 0; i < lines.length; i++)
+                pw.println(lines[i]);
+            pw.close();
+        }
+        catch (IOException e) {
+            e.printStackTrace();
+        }
+    }
+
+    // Berechnen des Hashwerts zu einem String und
+    // Rückgabe als Hex-Zeichenkette
+    public static String getHash(String w) {
+        try {
+            byte[] bytesOfMessage = w.getBytes("UTF-8");
+            MessageDigest md = MessageDigest.getInstance("MD5");
+            byte[] thedigest = md.digest(bytesOfMessage);
+            return String.format("%032x", new BigInteger(1, thedigest));
+        } catch (UnsupportedEncodingException | NoSuchAlgorithmException e) {
+            e.printStackTrace();
+        }
+        return null;
+    }
+
+}
diff --git a/Numbers.java b/Numbers.java
index 9f74f61..d9a2423 100644
--- a/Numbers.java
+++ b/Numbers.java
@@ -1,5 +1,7 @@
 public class Numbers {
 
+    private int number;
+
     public static void main(String[] args) {
         for (int i = 1; i <= 200; i++) {
             if (isDivisibleBy(5, i)) {
@@ -28,8 +30,12 @@ public class Numbers {
         }
     }
 
+    public static int sumWithPredecessor(int number) {
+        return 2 * number -1;
+    }
+
     public static boolean sumWithPredecessorIsDivisibleBy( int divisor, int number) {
-        int s = 2 * number - 1;
+        int s = sumWithPredecessor(number);
         if (isDivisibleBy(divisor, s)) {
             return true;
         } else {
diff --git a/NumbersTest.java b/NumbersTest.java
new file mode 100644
index 0000000..526c7a0
--- /dev/null
+++ b/NumbersTest.java
@@ -0,0 +1,56 @@
+import org.junit.jupiter.api.Test;
+import static org.junit.jupiter.api.Assertions.*;
+
+class NumbersTest {
+
+    @org.junit.jupiter.api.Test
+    void isDivisibleBy() {
+        Numbers number = new Numbers();
+        assertTrue(number.isDivisibleBy(3 ,12));
+        assertTrue(number.isDivisibleBy(4,12));
+        assertTrue(number.isDivisibleBy(6,12));
+        assertTrue(number.isDivisibleBy(12, 12));
+        assertFalse(number.isDivisibleBy(5,12));
+
+        assertTrue(number.isDivisibleBy(3 ,9));
+        assertTrue(number.isDivisibleBy(9, 9));
+        assertFalse(number.isDivisibleBy(4,9));
+        assertFalse(number.isDivisibleBy(5,9));
+        assertFalse(number.isDivisibleBy(6,9));
+    }
+
+    @org.junit.jupiter.api.Test
+    void lastDigitIs() {
+        Numbers number = new Numbers();
+        assertTrue(number.lastDigitIs(0, 90));
+        assertTrue(number.lastDigitIs(1, 1));
+        assertTrue(number.lastDigitIs(1, 41));
+        assertTrue(number.lastDigitIs(2, 32));
+        assertTrue(number.lastDigitIs(7, 67));
+        assertTrue(number.lastDigitIs(9, 10399));
+
+        assertFalse(number.lastDigitIs(1, 12));
+        assertFalse(number.lastDigitIs(2, 23));
+        assertFalse(number.lastDigitIs(10, 110));
+        assertFalse(number.lastDigitIs(5, 551));
+    }
+
+    @org.junit.jupiter.api.Test
+    void sumWithPredecessor() {
+        Numbers number = new Numbers();
+        assertEquals(11, number.sumWithPredecessor(6));
+        assertEquals(0, number.sumWithPredecessor(1));
+    }
+
+    @org.junit.jupiter.api.Test
+    void sumWithPredecessorIsDivisibleBy() {
+        Numbers number = new Numbers();
+        assertTrue(number.sumWithPredecessorIsDivisibleBy(1,14));
+        assertTrue(number.sumWithPredecessorIsDivisibleBy(3,14));
+        assertFalse(number.sumWithPredecessorIsDivisibleBy(4,36));
+        assertTrue(number.sumWithPredecessorIsDivisibleBy(5,18));
+        assertFalse(number.sumWithPredecessorIsDivisibleBy(10,100));
+        assertFalse(number.sumWithPredecessorIsDivisibleBy(12,24));
+        assertTrue(number.sumWithPredecessorIsDivisibleBy(13,85));
+    }
+}
\ No newline at end of file
diff --git a/prog3.iml b/prog3.iml
index 8b2ade9..762e558 100644
--- a/prog3.iml
+++ b/prog3.iml
@@ -7,5 +7,21 @@
     </content>
     <orderEntry type="inheritedJdk" />
     <orderEntry type="sourceFolder" forTests="false" />
+    <orderEntry type="module-library">
+      <library name="JUnit5.8.1">
+        <CLASSES>
+          <root url="jar://$MAVEN_REPOSITORY$/org/junit/jupiter/junit-jupiter/5.8.1/junit-jupiter-5.8.1.jar!/" />
+          <root url="jar://$MAVEN_REPOSITORY$/org/junit/jupiter/junit-jupiter-api/5.8.1/junit-jupiter-api-5.8.1.jar!/" />
+          <root url="jar://$MAVEN_REPOSITORY$/org/opentest4j/opentest4j/1.2.0/opentest4j-1.2.0.jar!/" />
+          <root url="jar://$MAVEN_REPOSITORY$/org/junit/platform/junit-platform-commons/1.8.1/junit-platform-commons-1.8.1.jar!/" />
+          <root url="jar://$MAVEN_REPOSITORY$/org/apiguardian/apiguardian-api/1.1.2/apiguardian-api-1.1.2.jar!/" />
+          <root url="jar://$MAVEN_REPOSITORY$/org/junit/jupiter/junit-jupiter-params/5.8.1/junit-jupiter-params-5.8.1.jar!/" />
+          <root url="jar://$MAVEN_REPOSITORY$/org/junit/jupiter/junit-jupiter-engine/5.8.1/junit-jupiter-engine-5.8.1.jar!/" />
+          <root url="jar://$MAVEN_REPOSITORY$/org/junit/platform/junit-platform-engine/1.8.1/junit-platform-engine-1.8.1.jar!/" />
+        </CLASSES>
+        <JAVADOC />
+        <SOURCES />
+      </library>
+    </orderEntry>
   </component>
 </module>
\ No newline at end of file