diff --git a/cas/1.2/IMediaCasService.hal b/cas/1.2/IMediaCasService.hal
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+++ b/cas/1.2/IMediaCasService.hal
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+/*
+ * Copyright (C) 2019 The Android Open Source Project
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *      http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+package android.hardware.cas@1.2;
+
+import ICas;
+import ICasListener;
+import @1.1::IMediaCasService;
+
+/**
+ * IMediaCasService is the main entry point for interacting with a vendor's
+ * cas HAL to create cas and descrambler plugin instances. A cas plugin instance
+ * opens cas sessions which are used to obtain keys for a descrambler session,
+ * which can in turn be used to descramble protected video content.
+ *
+ * The 1.2 must always create 1.2 ICas interfaces, which are
+ * returned via the 1.1 createPluginExt method.
+ *
+ * To use 1.2 features the caller must cast the returned interface to a
+ * 1.2 HAL, using V1_2::ICas::castFrom().
+ */
+interface IMediaCasService extends @1.1::IMediaCasService {};