From 0be4815edc4c13ceeb53f5b90e8fc54010289481 Mon Sep 17 00:00:00 2001
From: Ramji Chandramouli <ramjic@google.com>
Date: Thu, 16 Oct 2014 09:18:30 -0700
Subject: [PATCH] Use only the first 16 bytes of the asset key. Bug: 18003864

Change-Id: I65b08c4766a4c2ab08b09660b1540630387ab36c
---
 .../media/formats/wvm/wvm_media_parser.cc     | 15 ++++++++++++++-
 .../formats/wvm/wvm_media_parser_unittest.cc  | 19 +++++++++++++++++++
 2 files changed, 33 insertions(+), 1 deletion(-)

diff --git a/packager/media/formats/wvm/wvm_media_parser.cc b/packager/media/formats/wvm/wvm_media_parser.cc
index 9f30e66106..dbdc2a56c1 100644
--- a/packager/media/formats/wvm/wvm_media_parser.cc
+++ b/packager/media/formats/wvm/wvm_media_parser.cc
@@ -61,6 +61,7 @@ namespace {
   const uint32_t kEcmFlagsSizeBytes =
       kEcmCCIFlagsSizeBytes + kEcmDCPFlagsSizeBytes;
   const uint32_t kEcmPaddingSizeBytes = 12;
+  const uint32_t kAssetKeySizeBytes = 16;
 
   enum Type {
     Type_void = 0,
@@ -963,9 +964,21 @@ bool WvmMediaParser::ProcessEcm() {
   if (!GetAssetKey(asset_id, &encryption_key)) {
     return false;
   }
+  if (encryption_key.key.size() < kAssetKeySizeBytes) {
+    LOG(ERROR) << "Asset Key size of " << encryption_key.key.size()
+               << " for AssetID = " << asset_id
+               << " is less than minimum asset key size.";
+    return false;
+  }
+  // Legacy WVM content may have asset keys > 16 bytes.
+  // Use only the first 16 bytes of the asset key to get
+  // the content key.
+  std::vector<uint8_t> asset_key(
+      encryption_key.key.begin(),
+      encryption_key.key.begin() + kAssetKeySizeBytes);
   std::vector<uint8_t> iv(kInitializationVectorSizeBytes);
   AesCbcCtsDecryptor asset_decryptor;
-  if (!asset_decryptor.InitializeWithIv(encryption_key.key, iv)) {
+  if (!asset_decryptor.InitializeWithIv(asset_key, iv)) {
     LOG(ERROR) << "Failed to initialize asset_decryptor.";
     return false;
   }
diff --git a/packager/media/formats/wvm/wvm_media_parser_unittest.cc b/packager/media/formats/wvm/wvm_media_parser_unittest.cc
index c97ace7ff2..a86552c805 100644
--- a/packager/media/formats/wvm/wvm_media_parser_unittest.cc
+++ b/packager/media/formats/wvm/wvm_media_parser_unittest.cc
@@ -30,6 +30,11 @@ const int kExpectedVideoFrameCount = 6665;
 const int kExpectedAudioFrameCount = 11964;
 const uint8_t kExpectedAssetKey[] =
     "\x06\x81\x7f\x48\x6b\xf2\x7f\x3e\xc7\x39\xa8\x3f\x12\x0a\xd2\xfc";
+const uint8_t k64ByteAssetKey[] =
+    "\x06\x81\x7f\x48\x6b\xf2\x7f\x3e\xc7\x39\xa8\x3f\x12\x0a\xd2\xfc"
+    "\x06\x81\x7f\x48\x6b\xf2\x7f\x3e\xc7\x39\xa8\x3f\x12\x0a\xd2\xfc"
+    "\x06\x81\x7f\x48\x6b\xf2\x7f\x3e\xc7\x39\xa8\x3f\x12\x0a\xd2\xfc"
+    "\x06\x81\x7f\x48\x6b\xf2\x7f\x3e\xc7\x39\xa8\x3f\x12\x0a\xd2\xfc";
 const size_t kInitDataSize = 0x4000;
 }  // namespace
 
@@ -65,6 +70,7 @@ class WvmMediaParserTest : public testing::Test {
         current_track_id_(-1) {
     parser_.reset(new WvmMediaParser());
     key_source_.reset(new MockKeySource());
+    encryption_key_.key.resize(16);
     encryption_key_.key.assign(kExpectedAssetKey, kExpectedAssetKey + 16);
   }
 
@@ -169,6 +175,19 @@ TEST_F(WvmMediaParserTest, ParseWvm) {
   EXPECT_EQ(kExpectedAudioFrameCount, audio_frame_count_);
 }
 
+TEST_F(WvmMediaParserTest, ParseWvmWith64ByteAssetKey) {
+  EXPECT_CALL(*key_source_, FetchKeys(_)).WillOnce(Return(Status::OK));
+  // WVM uses only the first 16 bytes of the asset key.
+  encryption_key_.key.resize(64);
+  encryption_key_.key.assign(k64ByteAssetKey, k64ByteAssetKey + 64);
+  EXPECT_CALL(*key_source_, GetKey(_, _))
+      .WillOnce(DoAll(SetArgPointee<1>(encryption_key_), Return(Status::OK)));
+  Parse(kWvmFile);
+  EXPECT_EQ(kExpectedStreams, stream_map_.size());
+  EXPECT_EQ(kExpectedVideoFrameCount, video_frame_count_);
+  EXPECT_EQ(kExpectedAudioFrameCount, audio_frame_count_);
+}
+
 }  // namespace wvm
 }  // namespace media
 }  // namespace edash_packager