diff --git a/biometrics/face/aidl/default/Session.cpp b/biometrics/face/aidl/default/Session.cpp
index d980c5f..0cb7c95 100644
--- a/biometrics/face/aidl/default/Session.cpp
+++ b/biometrics/face/aidl/default/Session.cpp
@@ -34,12 +34,15 @@
     }
 };
 
-Session::Session(std::shared_ptr<ISessionCallback> cb) : cb_(std::move(cb)) {}
+Session::Session(std::shared_ptr<ISessionCallback> cb)
+    : cb_(std::move(cb)), mRandom(std::mt19937::default_seed) {}
 
 ndk::ScopedAStatus Session::generateChallenge() {
     LOG(INFO) << "generateChallenge";
     if (cb_) {
-        cb_->onChallengeGenerated(0);
+        std::uniform_int_distribution<int64_t> dist;
+        auto challenge = dist(mRandom);
+        cb_->onChallengeGenerated(challenge);
     }
     return ndk::ScopedAStatus::ok();
 }
@@ -63,6 +66,9 @@
         const std::vector<Feature>& /*features*/, const NativeHandle& /*previewSurface*/,
         std::shared_ptr<biometrics::common::ICancellationSignal>* /*return_val*/) {
     LOG(INFO) << "enroll";
+    if (cb_) {
+        cb_->onError(Error::UNABLE_TO_PROCESS, 0 /* vendorError */);
+    }
     return ndk::ScopedAStatus::ok();
 }
 
@@ -100,6 +106,9 @@
 
 ndk::ScopedAStatus Session::getFeatures() {
     LOG(INFO) << "getFeatures";
+    if (cb_) {
+        cb_->onFeaturesRetrieved({});
+    }
     return ndk::ScopedAStatus::ok();
 }
 
@@ -119,6 +128,9 @@
 
 ndk::ScopedAStatus Session::invalidateAuthenticatorId() {
     LOG(INFO) << "invalidateAuthenticatorId";
+    if (cb_) {
+        cb_->onAuthenticatorIdInvalidated(0);
+    }
     return ndk::ScopedAStatus::ok();
 }
 
diff --git a/biometrics/face/aidl/default/Session.h b/biometrics/face/aidl/default/Session.h
index caf81f8..4d213e3 100644
--- a/biometrics/face/aidl/default/Session.h
+++ b/biometrics/face/aidl/default/Session.h
@@ -16,6 +16,8 @@
 
 #pragma once
 
+#include <random>
+
 #include <aidl/android/hardware/biometrics/face/BnSession.h>
 #include <aidl/android/hardware/biometrics/face/ISessionCallback.h>
 
@@ -68,6 +70,7 @@
 
   private:
     std::shared_ptr<ISessionCallback> cb_;
+    std::mt19937 mRandom;
 };
 
 }  // namespace aidl::android::hardware::biometrics::face