diff --git a/keystore/Android.bp b/keystore/Android.bp
index cb736b3..68dde3d 100644
--- a/keystore/Android.bp
+++ b/keystore/Android.bp
@@ -84,6 +84,7 @@
     srcs: ["keystore_cli.cpp"],
     shared_libs: [
         "android.hardware.keymaster@3.0",
+        "android.hardware.keymaster@4.0",
         "libbinder",
         "libcrypto",
         "libcutils",
@@ -109,8 +110,8 @@
     srcs: ["keystore_cli_v2.cpp"],
     shared_libs: [
         "android.hardware.confirmationui@1.0",
-        "android.hardware.keymaster@3.0",
         "libbinder",
+        "android.hardware.keymaster@4.0",
         "libchrome",
         "libutils",
         "libhidlbase",
diff --git a/keystore/include/keystore/keymaster_types.h b/keystore/include/keystore/keymaster_types.h
index 62b43be..bd61294 100644
--- a/keystore/include/keystore/keymaster_types.h
+++ b/keystore/include/keystore/keymaster_types.h
@@ -83,6 +83,7 @@
 using keymaster::TAG_RSA_PUBLIC_EXPONENT;
 using keymaster::TAG_USAGE_EXPIRE_DATETIME;
 using keymaster::TAG_USER_AUTH_TYPE;
+using keymaster::TAG_USER_ID;
 using keymaster::TAG_USER_SECURE_ID;
 
 using keymaster::NullOr;
diff --git a/keystore/key_store_service.cpp b/keystore/key_store_service.cpp
index 96d8f4d..582f8aa 100644
--- a/keystore/key_store_service.cpp
+++ b/keystore/key_store_service.cpp
@@ -364,6 +364,7 @@
         return Status::ok();
     }
 
+    enforcement_policy.set_device_locked(true, userId);
     mKeyStore->lock(userId);
     *aidl_return = static_cast<int32_t>(ResponseCode::NO_ERROR);
     return Status::ok();
@@ -392,6 +393,7 @@
         return Status::ok();
     }
 
+    enforcement_policy.set_device_locked(false, userId);
     const String8 password8(pw);
     // read master key, decrypt with password, initialize mMasterKey*.
     *aidl_return = static_cast<int32_t>(mKeyStore->readMasterKey(password8, userId));
@@ -1444,7 +1446,7 @@
 }
 
 Status KeyStoreService::addAuthToken(const ::std::vector<uint8_t>& authTokenAsVector,
-                                     int32_t* aidl_return) {
+                                     int32_t android_uid, int32_t* aidl_return) {
 
     // TODO(swillden): When gatekeeper and fingerprint are ready, this should be updated to
     // receive a HardwareAuthToken, rather than an opaque byte array.
@@ -1466,6 +1468,8 @@
         return Status::ok();
     }
 
+    enforcement_policy.set_device_locked(false, android_uid);
+
     mAuthTokenTable.AddAuthenticationToken(hidlVec2AuthToken(hidl_vec<uint8_t>(authTokenAsVector)));
     *aidl_return = static_cast<int32_t>(ResponseCode::NO_ERROR);
     return Status::ok();
diff --git a/keystore/key_store_service.h b/keystore/key_store_service.h
index ce809f8..ea4a089 100644
--- a/keystore/key_store_service.h
+++ b/keystore/key_store_service.h
@@ -146,7 +146,7 @@
     ::android::binder::Status isOperationAuthorized(const ::android::sp<::android::IBinder>& token,
                                                     bool* _aidl_return) override;
     ::android::binder::Status addAuthToken(const ::std::vector<uint8_t>& authToken,
-                                           int32_t* _aidl_return) override;
+                                           int32_t android_uid, int32_t* _aidl_return) override;
     ::android::binder::Status onUserAdded(int32_t userId, int32_t parentId,
                                           int32_t* _aidl_return) override;
     ::android::binder::Status onUserRemoved(int32_t userId, int32_t* _aidl_return) override;
diff --git a/keystore/keymaster_enforcement.cpp b/keystore/keymaster_enforcement.cpp
index d78a5a6..690927c 100644
--- a/keystore/keymaster_enforcement.cpp
+++ b/keystore/keymaster_enforcement.cpp
@@ -223,6 +223,8 @@
     bool caller_nonce_authorized_by_key = false;
     bool authentication_required = false;
     bool auth_token_matched = false;
+    bool unlocked_device_required = false;
+    int32_t user_id = -1;
 
     for (auto& param : auth_set) {
 
@@ -282,10 +284,18 @@
             }
             break;
 
+        case Tag::USER_ID:
+            user_id = authorizationValue(TAG_USER_ID, param).value();
+            break;
+
         case Tag::CALLER_NONCE:
             caller_nonce_authorized_by_key = true;
             break;
 
+        case Tag::UNLOCKED_DEVICE_REQUIRED:
+            unlocked_device_required = true;
+            break;
+
         /* Tags should never be in key auths. */
         case Tag::INVALID:
         case Tag::ROOT_OF_TRUST:
@@ -356,6 +366,10 @@
         }
     }
 
+    if (unlocked_device_required && is_device_locked(user_id)) {
+        return ErrorCode::DEVICE_LOCKED;
+    }
+
     if (authentication_required && !auth_token_matched) {
         ALOGE("Auth required but no matching auth token found");
         return ErrorCode::KEY_USER_NOT_AUTHENTICATED;
diff --git a/keystore/keymaster_enforcement.h b/keystore/keymaster_enforcement.h
index d7b27fc..6e6c54f 100644
--- a/keystore/keymaster_enforcement.h
+++ b/keystore/keymaster_enforcement.h
@@ -142,6 +142,11 @@
      */
     virtual bool ValidateTokenSignature(const HardwareAuthToken& token) const = 0;
 
+    /*
+     * Returns true if the device screen is currently locked for the specified user.
+     */
+    virtual bool is_device_locked(int32_t userId) const = 0;
+
   private:
     ErrorCode AuthorizeUpdateOrFinish(const AuthorizationSet& auth_set,
                                       const HardwareAuthToken& auth_token, uint64_t op_handle);
diff --git a/keystore/keystore_keymaster_enforcement.h b/keystore/keystore_keymaster_enforcement.h
index 3cdf649..e114ea9 100644
--- a/keystore/keystore_keymaster_enforcement.h
+++ b/keystore/keystore_keymaster_enforcement.h
@@ -84,6 +84,19 @@
         // signing key. Assume the token is good.
         return true;
     }
+
+    bool is_device_locked(int32_t userId) const override {
+        // If we haven't had a set call for this user yet, assume the device is locked.
+        if (mIsDeviceLockedForUser.count(userId) == 0) return true;
+        return mIsDeviceLockedForUser.find(userId)->second;
+    }
+
+    void set_device_locked(bool isLocked, int32_t userId) {
+        mIsDeviceLockedForUser[userId] = isLocked;
+    }
+
+  private:
+    std::map<int32_t, bool> mIsDeviceLockedForUser;
 };
 
 } // namespace keystore