diff --git a/NOTICE b/NOTICE
index 447c1f1a..274e6614 100644
--- a/NOTICE
+++ b/NOTICE
@@ -16,3 +16,4 @@ Michael Schulte [mschulte-tsi], T-Systems International GmbH
 Lars Stelzner [lstelzne-tech], T-Systems International GmbH
 Andreas Mandel [amandel], T-Systems International GmbH
 Martin Scheffler [martinschefflerTSI] T-Systems International GmbH
+Damir Seit [damirseit], Nazarbayev University
diff --git a/src/main/java/app/coronawarn/verification/controller/ExternalTanController.java b/src/main/java/app/coronawarn/verification/controller/ExternalTanController.java
index 6469340c..32ca3fb0 100644
--- a/src/main/java/app/coronawarn/verification/controller/ExternalTanController.java
+++ b/src/main/java/app/coronawarn/verification/controller/ExternalTanController.java
@@ -25,13 +25,13 @@
 import app.coronawarn.verification.config.VerificationApplicationConfig;
 import app.coronawarn.verification.domain.VerificationAppSession;
 import app.coronawarn.verification.exception.VerificationServerException;
+import app.coronawarn.verification.factories.tan.verifier.TanVerifier;
+import app.coronawarn.verification.factories.tan.verifier.TanVerifierFactory;
+import app.coronawarn.verification.factories.tan.verifier.TanVerifierFactoryImpl;
 import app.coronawarn.verification.model.AppSessionSourceOfTrust;
-import app.coronawarn.verification.model.HashedGuid;
-import app.coronawarn.verification.model.LabTestResult;
 import app.coronawarn.verification.model.RegistrationToken;
 import app.coronawarn.verification.model.Tan;
 import app.coronawarn.verification.model.TanSourceOfTrust;
-import app.coronawarn.verification.model.TestResult;
 import app.coronawarn.verification.service.AppSessionService;
 import app.coronawarn.verification.service.FakeDelayService;
 import app.coronawarn.verification.service.FakeRequestService;
@@ -98,6 +98,9 @@ public class ExternalTanController {
   @NonNull
   private final FakeRequestService fakeRequestService;
 
+  @NonNull
+  private final TanVerifierFactory tanVerifierFactory;
+
   /**
    * This method generates a transaction number by a Registration Token, if the state of the COVID-19 lab-test is
    * positive.
@@ -133,25 +136,11 @@ public DeferredResult<ResponseEntity<Tan>> generateTan(@Valid @RequestBody Regis
       if (appSession.getTanCounter() < tancountermax) {
         AppSessionSourceOfTrust appSessionSourceOfTrust = appSession.getSourceOfTrust();
         TanSourceOfTrust tanSourceOfTrust = TanSourceOfTrust.CONNECTED_LAB;
-        switch (appSessionSourceOfTrust) {
-          case HASHED_GUID:
-            TestResult covidTestResult = testResultServerService.result(new HashedGuid(appSession.getHashedGuid()));
-            if (covidTestResult.getTestResult() != LabTestResult.POSITIVE.getTestResult()
-              && covidTestResult.getTestResult() != LabTestResult.QUICK_POSITIVE.getTestResult()
-            ) {
-              stopWatch.stop();
-              throw new VerificationServerException(HttpStatus.BAD_REQUEST,
-                "Tan cannot be created, caused by the non positive result of the labserver");
-            }
-            break;
-          case TELETAN:
-            tanSourceOfTrust = TanSourceOfTrust.TELETAN;
-            break;
-          default:
-            stopWatch.stop();
-            throw new VerificationServerException(HttpStatus.BAD_REQUEST,
-              "Unknown source of trust inside the appsession for the registration token");
-        }
+
+        TanVerifier tanVerifier = tanVerifierFactory.makeTanVerifier(appSessionSourceOfTrust);
+
+        tanVerifier.generateTan(appSession, testResultServerService, stopWatch, tanSourceOfTrust);
+
         appSession.incrementTanCounter();
         appSession.setUpdatedAt(LocalDateTime.now());
 
diff --git a/src/main/java/app/coronawarn/verification/factories/tan/verifier/HashedGuidTanVerifier.java b/src/main/java/app/coronawarn/verification/factories/tan/verifier/HashedGuidTanVerifier.java
new file mode 100644
index 00000000..f2ebd7dd
--- /dev/null
+++ b/src/main/java/app/coronawarn/verification/factories/tan/verifier/HashedGuidTanVerifier.java
@@ -0,0 +1,28 @@
+package app.coronawarn.verification.factories.tan.verifier;
+
+import app.coronawarn.verification.domain.VerificationAppSession;
+import app.coronawarn.verification.exception.VerificationServerException;
+import app.coronawarn.verification.model.HashedGuid;
+import app.coronawarn.verification.model.LabTestResult;
+import app.coronawarn.verification.model.TanSourceOfTrust;
+import app.coronawarn.verification.model.TestResult;
+import app.coronawarn.verification.service.TestResultServerService;
+import org.springframework.http.HttpStatus;
+import org.springframework.util.StopWatch;
+
+public class HashedGuidTanVerifier extends TanVerifier {
+  @Override
+  public void generateTan(VerificationAppSession appSession,
+                          TestResultServerService testResultServerService,
+                          StopWatch stopWatch,
+                          TanSourceOfTrust tanSourceOfTrust) {
+    TestResult covidTestResult = testResultServerService.result(new HashedGuid(appSession.getHashedGuid()));
+    if (covidTestResult.getTestResult() != LabTestResult.POSITIVE.getTestResult()
+      && covidTestResult.getTestResult() != LabTestResult.QUICK_POSITIVE.getTestResult()
+    ) {
+      stopWatch.stop();
+      throw new VerificationServerException(HttpStatus.BAD_REQUEST,
+        "Tan cannot be created, caused by the non positive result of the labserver");
+    }
+  }
+}
diff --git a/src/main/java/app/coronawarn/verification/factories/tan/verifier/TanVerifier.java b/src/main/java/app/coronawarn/verification/factories/tan/verifier/TanVerifier.java
new file mode 100644
index 00000000..5eae5f80
--- /dev/null
+++ b/src/main/java/app/coronawarn/verification/factories/tan/verifier/TanVerifier.java
@@ -0,0 +1,13 @@
+package app.coronawarn.verification.factories.tan.verifier;
+
+import app.coronawarn.verification.domain.VerificationAppSession;
+import app.coronawarn.verification.model.TanSourceOfTrust;
+import app.coronawarn.verification.service.TestResultServerService;
+import org.springframework.util.StopWatch;
+
+public abstract class TanVerifier {
+  public abstract void generateTan(VerificationAppSession appSession,
+                                   TestResultServerService testResultServerService,
+                                   StopWatch stopWatch,
+                                   TanSourceOfTrust tanSourceOfTrust);
+}
diff --git a/src/main/java/app/coronawarn/verification/factories/tan/verifier/TanVerifierFactory.java b/src/main/java/app/coronawarn/verification/factories/tan/verifier/TanVerifierFactory.java
new file mode 100644
index 00000000..99a805d5
--- /dev/null
+++ b/src/main/java/app/coronawarn/verification/factories/tan/verifier/TanVerifierFactory.java
@@ -0,0 +1,7 @@
+package app.coronawarn.verification.factories.tan.verifier;
+
+import app.coronawarn.verification.model.AppSessionSourceOfTrust;
+
+public interface TanVerifierFactory {
+  public TanVerifier makeTanVerifier(AppSessionSourceOfTrust appSessionSourceOfTrust);
+}
diff --git a/src/main/java/app/coronawarn/verification/factories/tan/verifier/TanVerifierFactoryImpl.java b/src/main/java/app/coronawarn/verification/factories/tan/verifier/TanVerifierFactoryImpl.java
new file mode 100644
index 00000000..a52ea3d9
--- /dev/null
+++ b/src/main/java/app/coronawarn/verification/factories/tan/verifier/TanVerifierFactoryImpl.java
@@ -0,0 +1,17 @@
+package app.coronawarn.verification.factories.tan.verifier;
+
+import app.coronawarn.verification.model.AppSessionSourceOfTrust;
+
+public class TanVerifierFactoryImpl implements TanVerifierFactory {
+  @Override
+  public TanVerifier makeTanVerifier(AppSessionSourceOfTrust appSessionSourceOfTrust) {
+    switch (appSessionSourceOfTrust) {
+      case HASHED_GUID:
+        return new HashedGuidTanVerifier();
+      case TELETAN:
+        return new TeletanTanVerifier();
+      default:
+        return new UnknownTanVerifier();
+    }
+  }
+}
diff --git a/src/main/java/app/coronawarn/verification/factories/tan/verifier/TeletanTanVerifier.java b/src/main/java/app/coronawarn/verification/factories/tan/verifier/TeletanTanVerifier.java
new file mode 100644
index 00000000..ea183ba3
--- /dev/null
+++ b/src/main/java/app/coronawarn/verification/factories/tan/verifier/TeletanTanVerifier.java
@@ -0,0 +1,17 @@
+package app.coronawarn.verification.factories.tan.verifier;
+
+import app.coronawarn.verification.domain.VerificationAppSession;
+import app.coronawarn.verification.model.TanSourceOfTrust;
+import app.coronawarn.verification.service.TestResultServerService;
+import org.springframework.util.StopWatch;
+
+public class TeletanTanVerifier extends TanVerifier {
+
+  @Override
+  public void generateTan(VerificationAppSession appSession,
+                          TestResultServerService testResultServerService,
+                          StopWatch stopWatch,
+                          TanSourceOfTrust tanSourceOfTrust) {
+    tanSourceOfTrust = TanSourceOfTrust.TELETAN;
+  }
+}
diff --git a/src/main/java/app/coronawarn/verification/factories/tan/verifier/UnknownTanVerifier.java b/src/main/java/app/coronawarn/verification/factories/tan/verifier/UnknownTanVerifier.java
new file mode 100644
index 00000000..a542ddc3
--- /dev/null
+++ b/src/main/java/app/coronawarn/verification/factories/tan/verifier/UnknownTanVerifier.java
@@ -0,0 +1,20 @@
+package app.coronawarn.verification.factories.tan.verifier;
+
+import app.coronawarn.verification.domain.VerificationAppSession;
+import app.coronawarn.verification.exception.VerificationServerException;
+import app.coronawarn.verification.model.TanSourceOfTrust;
+import app.coronawarn.verification.service.TestResultServerService;
+import org.springframework.http.HttpStatus;
+import org.springframework.util.StopWatch;
+
+public class UnknownTanVerifier extends TanVerifier {
+  @Override
+  public void generateTan(VerificationAppSession appSession,
+                          TestResultServerService testResultServerService,
+                          StopWatch stopWatch,
+                          TanSourceOfTrust tanSourceOfTrust) {
+    stopWatch.stop();
+    throw new VerificationServerException(HttpStatus.BAD_REQUEST,
+      "Unknown source of trust inside the appsession for the registration token");
+  }
+}