diff --git a/libwvdrmengine/cdm/core/include/cdm_session.h b/libwvdrmengine/cdm/core/include/cdm_session.h
index 4a96a576..9a727189 100644
--- a/libwvdrmengine/cdm/core/include/cdm_session.h
+++ b/libwvdrmengine/cdm/core/include/cdm_session.h
@@ -23,7 +23,8 @@ class WvCdmEventListener;
 class CdmSession {
  public:
   CdmSession(const CdmClientPropertySet* cdm_client_property_set,
-             const std::string& origin, WvCdmEventListener* event_listener);
+             const std::string& origin, WvCdmEventListener* event_listener,
+             CdmSessionId* forced_session_id);
   virtual ~CdmSession();
 
   virtual CdmResponseType Init();
diff --git a/libwvdrmengine/cdm/core/include/device_files.h b/libwvdrmengine/cdm/core/include/device_files.h
index 840a673a..57f29fe7 100644
--- a/libwvdrmengine/cdm/core/include/device_files.h
+++ b/libwvdrmengine/cdm/core/include/device_files.h
@@ -4,6 +4,7 @@
 #define WVCDM_CORE_DEVICE_FILES_H_
 
 #include <unistd.h>
+#include <set>
 #include <string>
 
 #include "scoped_ptr.h"
@@ -110,7 +111,6 @@ class DeviceFiles {
   static std::string GetCertificateFileName(const std::string& origin);
   static std::string GetLicenseFileNameExtension();
   static std::string GetUsageInfoFileName(const std::string& app_id);
-  static std::string GetBlankFileData();
   static std::string GetFileNameSafeHash(const std::string& input);
 
   // For testing only:
@@ -122,7 +122,7 @@ class DeviceFiles {
   FRIEND_TEST(DeviceCertificateTest, HasCertificate);
   FRIEND_TEST(DeviceFilesStoreTest, StoreLicense);
   FRIEND_TEST(DeviceFilesTest, DeleteLicense);
-  FRIEND_TEST(DeviceFilesTest, ReserveLicenseIds);
+  FRIEND_TEST(DeviceFilesTest, ReserveLicenseIdsDoesNotUseFileSystem);
   FRIEND_TEST(DeviceFilesTest, RetrieveLicenses);
   FRIEND_TEST(DeviceFilesTest, AppParametersBackwardCompatibility);
   FRIEND_TEST(DeviceFilesTest, SecurityLevelPathBackwardCompatibility);
@@ -141,6 +141,8 @@ class DeviceFiles {
   FRIEND_TEST(WvCdmExtendedDurationTest, UsageOverflowTest);
 #endif
 
+  static std::set<std::string> reserved_license_ids_;
+
   scoped_ptr<File> file_;
   CdmSecurityLevel security_level_;
   bool initialized_;
diff --git a/libwvdrmengine/cdm/core/include/properties.h b/libwvdrmengine/cdm/core/include/properties.h
index 8acf750c..a0890317 100644
--- a/libwvdrmengine/cdm/core/include/properties.h
+++ b/libwvdrmengine/cdm/core/include/properties.h
@@ -54,6 +54,7 @@ class Properties {
                                      std::string* base_path);
   static bool GetFactoryKeyboxPath(std::string* keybox);
   static bool GetOEMCryptoPath(std::string* library_name);
+  static bool AlwaysUseKeySetIds();
   static bool GetSecurityLevelDirectories(std::vector<std::string>* dirs);
   static bool GetApplicationId(const CdmSessionId& session_id,
                                std::string* app_id);
diff --git a/libwvdrmengine/cdm/core/src/cdm_engine.cpp b/libwvdrmengine/cdm/core/src/cdm_engine.cpp
index 1bab8f63..3b7bf096 100644
--- a/libwvdrmengine/cdm/core/src/cdm_engine.cpp
+++ b/libwvdrmengine/cdm/core/src/cdm_engine.cpp
@@ -91,8 +91,13 @@ CdmResponseType CdmEngine::OpenSession(const CdmKeySystem& key_system,
     return INVALID_PARAMETERS_ENG_1;
   }
 
+  CdmSessionId* forced_session_id = NULL;
+  if (Properties::AlwaysUseKeySetIds() && !session_id->empty()) {
+    forced_session_id = session_id;
+  }
+
   scoped_ptr<CdmSession> new_session(
-      new CdmSession(property_set, origin, event_listener));
+      new CdmSession(property_set, origin, event_listener, forced_session_id));
   if (new_session->session_id().empty()) {
     LOGE("CdmEngine::OpenSession: failure to generate session ID");
     return EMPTY_SESSION_ID;
@@ -180,7 +185,10 @@ CdmResponseType CdmEngine::GenerateKeyRequest(
   CdmSessionId id = session_id;
   CdmResponseType sts;
 
-  if (license_type == kLicenseTypeRelease) {
+  // NOTE: If AlwaysUseKeySetIds() is true, there is no need to consult the
+  // release_key_sets_ map for release licenses.
+  if (license_type == kLicenseTypeRelease &&
+      !Properties::AlwaysUseKeySetIds()) {
     if (key_set_id.empty()) {
       LOGE("CdmEngine::GenerateKeyRequest: invalid key set ID");
       return EMPTY_KEYSET_ID_ENG_2;
@@ -666,7 +674,7 @@ CdmResponseType CdmEngine::GetUsageInfo(const std::string& app_id,
   usage_property_set_->set_security_level(kLevelDefault);
   usage_property_set_->set_app_id(app_id);
   usage_session_.reset(
-      new CdmSession(usage_property_set_.get(), EMPTY_ORIGIN, NULL));
+      new CdmSession(usage_property_set_.get(), EMPTY_ORIGIN, NULL, NULL));
   CdmResponseType status = usage_session_->Init();
   if (NO_ERROR != status) {
     LOGE("CdmEngine::GetUsageInfo: session init error");
@@ -685,7 +693,7 @@ CdmResponseType CdmEngine::GetUsageInfo(const std::string& app_id,
     usage_property_set_->set_security_level(kLevel3);
     usage_property_set_->set_app_id(app_id);
     usage_session_.reset(
-        new CdmSession(usage_property_set_.get(), EMPTY_ORIGIN, NULL));
+        new CdmSession(usage_property_set_.get(), EMPTY_ORIGIN, NULL, NULL));
     status = usage_session_->Init();
     if (NO_ERROR != status) {
       LOGE("CdmEngine::GetUsageInfo: session init error");
@@ -754,7 +762,7 @@ CdmResponseType CdmEngine::GetUsageInfo(const std::string& app_id,
   usage_property_set_->set_app_id(app_id);
 
   usage_session_.reset(
-      new CdmSession(usage_property_set_.get(), EMPTY_ORIGIN, NULL));
+      new CdmSession(usage_property_set_.get(), EMPTY_ORIGIN, NULL, NULL));
 
   CdmResponseType status = usage_session_->Init();
   if (NO_ERROR != status) {
@@ -833,7 +841,8 @@ CdmResponseType CdmEngine::ReleaseAllUsageInfo(const std::string& app_id) {
                 : kLevelDefault;
         usage_property_set_->set_security_level(security_level);
         usage_session_.reset(
-            new CdmSession(usage_property_set_.get(), EMPTY_ORIGIN, NULL));
+            new CdmSession(usage_property_set_.get(), EMPTY_ORIGIN, NULL,
+                           NULL));
         CdmResponseType status2 = usage_session_->
             DeleteMultipleUsageInformation(provider_session_tokens);
         if (status2 != NO_ERROR) {
diff --git a/libwvdrmengine/cdm/core/src/cdm_session.cpp b/libwvdrmengine/cdm/core/src/cdm_session.cpp
index a7c728ca..ddb8a662 100644
--- a/libwvdrmengine/cdm/core/src/cdm_session.cpp
+++ b/libwvdrmengine/cdm/core/src/cdm_session.cpp
@@ -25,14 +25,13 @@ namespace wvcdm {
 
 CdmSession::CdmSession(const CdmClientPropertySet* cdm_client_property_set,
                        const std::string& origin,
-                       WvCdmEventListener* event_listener)
+                       WvCdmEventListener* event_listener,
+                       CdmSessionId* forced_session_id)
     : initialized_(false),
       session_id_(GenerateSessionId()),
       origin_(origin),
       license_parser_(new CdmLicense),
       crypto_session_(new CryptoSession),
-      policy_engine_(
-          new PolicyEngine(session_id_, event_listener, crypto_session_.get())),
       file_handle_(new DeviceFiles),
       license_received_(false),
       is_offline_(false),
@@ -43,6 +42,17 @@ CdmSession::CdmSession(const CdmClientPropertySet* cdm_client_property_set,
       has_decrypted_since_last_report_(false),
       is_initial_usage_update_(true),
       is_usage_update_needed_(false) {
+  if (Properties::AlwaysUseKeySetIds()) {
+    if (forced_session_id) {
+      key_set_id_ = *forced_session_id;
+    } else {
+      bool ok = GenerateKeySetId(&key_set_id_);
+      assert(ok);
+    }
+    session_id_ = key_set_id_;
+  }
+  policy_engine_.reset(new PolicyEngine(
+      session_id_, event_listener, crypto_session_.get()));
   if (cdm_client_property_set) {
     if (cdm_client_property_set->security_level() ==
         QUERY_VALUE_SECURITY_LEVEL_L3) {
@@ -203,7 +213,8 @@ CdmResponseType CdmSession::GenerateKeyRequest(
       LOGW("CdmSession::GenerateKeyRequest: init data absent");
       return INIT_DATA_NOT_FOUND;
     }
-    if (is_offline_ && !GenerateKeySetId(&key_set_id_)) {
+    if (is_offline_ && key_set_id_.empty() &&
+        !GenerateKeySetId(&key_set_id_)) {
       LOGE("CdmSession::GenerateKeyRequest: Unable to generate key set ID");
       return KEY_REQUEST_ERROR_1;
     }
diff --git a/libwvdrmengine/cdm/core/src/device_files.cpp b/libwvdrmengine/cdm/core/src/device_files.cpp
index df0bbb9c..bc8ab008 100644
--- a/libwvdrmengine/cdm/core/src/device_files.cpp
+++ b/libwvdrmengine/cdm/core/src/device_files.cpp
@@ -46,8 +46,6 @@ const char* kSecurityLevelPathCompatibilityExclusionList[] = {
 size_t kSecurityLevelPathCompatibilityExclusionListSize =
     sizeof(kSecurityLevelPathCompatibilityExclusionList) /
     sizeof(*kSecurityLevelPathCompatibilityExclusionList);
-// Some platforms cannot store a truly blank file, so we use a W for Widevine.
-const char kBlankFileData[] = "W";
 
 bool Hash(const std::string& data, std::string* hash) {
   if (!hash) return false;
@@ -64,6 +62,9 @@ bool Hash(const std::string& data, std::string* hash) {
 
 namespace wvcdm {
 
+// static
+std::set<std::string> DeviceFiles::reserved_license_ids_;
+
 DeviceFiles::DeviceFiles()
     : file_(NULL),
       security_level_(kSecurityLevelUninitialized),
@@ -228,6 +229,7 @@ bool DeviceFiles::StoreLicense(
   std::string serialized_file;
   file.SerializeToString(&serialized_file);
 
+  reserved_license_ids_.erase(key_set_id);
   return StoreFileWithHash(key_set_id + kLicenseFileNameExt, serialized_file);
 }
 
@@ -331,6 +333,8 @@ bool DeviceFiles::LicenseExists(const std::string& key_set_id) {
     return false;
   }
   return FileExists(key_set_id + kLicenseFileNameExt);
+  return reserved_license_ids_.count(key_set_id) ||
+         FileExists(key_set_id + kLicenseFileNameExt);
 }
 
 bool DeviceFiles::ReserveLicenseId(const std::string& key_set_id) {
@@ -338,7 +342,8 @@ bool DeviceFiles::ReserveLicenseId(const std::string& key_set_id) {
     LOGW("DeviceFiles::ReserveLicenseId: not initialized");
     return false;
   }
-  return StoreFileRaw(key_set_id + kLicenseFileNameExt, kBlankFileData);
+  reserved_license_ids_.insert(key_set_id);
+  return true;
 }
 
 bool DeviceFiles::StoreUsageInfo(const std::string& provider_session_token,
@@ -804,8 +809,6 @@ std::string DeviceFiles::GetUsageInfoFileName(const std::string& app_id) {
   return kUsageInfoFileNamePrefix + hash + kUsageInfoFileNameExt;
 }
 
-std::string DeviceFiles::GetBlankFileData() { return kBlankFileData; }
-
 std::string DeviceFiles::GetFileNameSafeHash(const std::string& input) {
   std::vector<uint8_t> hash(MD5_DIGEST_LENGTH);
   const unsigned char* input_ptr =
diff --git a/libwvdrmengine/cdm/core/src/properties.cpp b/libwvdrmengine/cdm/core/src/properties.cpp
index fb0d4309..686f2e43 100644
--- a/libwvdrmengine/cdm/core/src/properties.cpp
+++ b/libwvdrmengine/cdm/core/src/properties.cpp
@@ -1,7 +1,7 @@
 // Copyright 2013 Google Inc. All Rights Reserved.
 
 #include "log.h"
-#include "properties_configuration.h"
+#include "properties.h"
 #include "wv_cdm_constants.h"
 
 namespace {
@@ -16,17 +16,6 @@ bool Properties::use_certificates_as_identification_;
 bool Properties::security_level_path_backward_compatibility_support_;
 scoped_ptr<CdmClientPropertySetMap> Properties::session_property_set_;
 
-void Properties::Init() {
-  oem_crypto_use_secure_buffers_ = kPropertyOemCryptoUseSecureBuffers;
-  oem_crypto_use_fifo_ = kPropertyOemCryptoUseFifo;
-  oem_crypto_use_userspace_buffers_ = kPropertyOemCryptoUseUserSpaceBuffers;
-  use_certificates_as_identification_ =
-      kPropertyUseCertificatesAsIdentification;
-  security_level_path_backward_compatibility_support_ =
-      kSecurityLevelPathBackwardCompatibilitySupport;
-  session_property_set_.reset(new CdmClientPropertySetMap());
-}
-
 bool Properties::AddSessionPropertySet(
     const CdmSessionId& session_id, const CdmClientPropertySet* property_set) {
   if (NULL == session_property_set_.get()) {
diff --git a/libwvdrmengine/cdm/core/test/cdm_session_unittest.cpp b/libwvdrmengine/cdm/core/test/cdm_session_unittest.cpp
index 1e4cd121..bcc8c953 100644
--- a/libwvdrmengine/cdm/core/test/cdm_session_unittest.cpp
+++ b/libwvdrmengine/cdm/core/test/cdm_session_unittest.cpp
@@ -132,7 +132,7 @@ class MockCdmLicense : public CdmLicense {
 class CdmSessionTest : public ::testing::Test {
  protected:
   virtual void SetUp() {
-    cdm_session_.reset(new CdmSession(NULL, kTestOrigin, NULL));
+    cdm_session_.reset(new CdmSession(NULL, kTestOrigin, NULL, NULL));
     // Inject testing mocks.
     license_parser_ = new MockCdmLicense();
     cdm_session_->set_license_parser(license_parser_);
diff --git a/libwvdrmengine/cdm/core/test/device_files_unittest.cpp b/libwvdrmengine/cdm/core/test/device_files_unittest.cpp
index e2647104..ab81d77d 100644
--- a/libwvdrmengine/cdm/core/test/device_files_unittest.cpp
+++ b/libwvdrmengine/cdm/core/test/device_files_unittest.cpp
@@ -2118,26 +2118,15 @@ TEST_F(DeviceFilesTest, DeleteLicense) {
   EXPECT_FALSE(device_files.LicenseExists(license_test_data[0].key_set_id));
 }
 
-TEST_F(DeviceFilesTest, ReserveLicenseIds) {
+TEST_F(DeviceFilesTest, ReserveLicenseIdsDoesNotUseFileSystem) {
+  // Validate that ReserveLicenseIds does not touch the file system.
   MockFile file;
-  EXPECT_CALL(file, IsDirectory(StrEq(device_base_path_)))
-      .Times(kNumberOfLicenses)
-      .WillRepeatedly(Return(true));
+  EXPECT_CALL(file, IsDirectory(StrEq(device_base_path_))).Times(0);
   EXPECT_CALL(file, CreateDirectory(_)).Times(0);
 
-  for (size_t i = 0; i < kNumberOfLicenses; ++i) {
-    std::string license_path = device_base_path_ +
-                               license_test_data[i].key_set_id +
-                               DeviceFiles::GetLicenseFileNameExtension();
-    InSequence calls;
-    EXPECT_CALL(file, Open(StrEq(license_path),
-                           AllOf(IsCreateFileFlagSet(), IsBinaryFileFlagSet())))
-        .WillOnce(Return(true));
-    EXPECT_CALL(file, Write(StrEq(DeviceFiles::GetBlankFileData()),
-                            DeviceFiles::GetBlankFileData().size()))
-        .WillOnce(ReturnArg<1>());
-    EXPECT_CALL(file, Close());
-  }
+  EXPECT_CALL(file, Open(_, _)).Times(0);
+  EXPECT_CALL(file, Write(_, _)).Times(0);
+  EXPECT_CALL(file, Close()).Times(0);
   EXPECT_CALL(file, Read(_, _)).Times(0);
 
   DeviceFiles device_files;
@@ -2145,6 +2134,8 @@ TEST_F(DeviceFilesTest, ReserveLicenseIds) {
   device_files.SetTestFile(&file);
   for (size_t i = 0; i < kNumberOfLicenses; i++) {
     EXPECT_TRUE(device_files.ReserveLicenseId(license_test_data[i].key_set_id));
+    // Validate that the license IDs are actually reserved.
+    EXPECT_TRUE(device_files.LicenseExists(license_test_data[i].key_set_id));
   }
 }
 
diff --git a/libwvdrmengine/cdm/src/properties_android.cpp b/libwvdrmengine/cdm/src/properties_android.cpp
index 97567742..6753f39b 100644
--- a/libwvdrmengine/cdm/src/properties_android.cpp
+++ b/libwvdrmengine/cdm/src/properties_android.cpp
@@ -1,6 +1,7 @@
 // Copyright 2013 Google Inc. All Rights Reserved.
 
 #include "properties.h"
+#include "properties_configuration.h"
 
 #include <unistd.h>
 #include <sstream>
@@ -42,6 +43,17 @@ bool GetAndroidProperty(const char* key, std::string* value) {
 
 namespace wvcdm {
 
+void Properties::Init() {
+  oem_crypto_use_secure_buffers_ = kPropertyOemCryptoUseSecureBuffers;
+  oem_crypto_use_fifo_ = kPropertyOemCryptoUseFifo;
+  oem_crypto_use_userspace_buffers_ = kPropertyOemCryptoUseUserSpaceBuffers;
+  use_certificates_as_identification_ =
+      kPropertyUseCertificatesAsIdentification;
+  security_level_path_backward_compatibility_support_ =
+      kSecurityLevelPathBackwardCompatibilitySupport;
+  session_property_set_.reset(new CdmClientPropertySetMap());
+}
+
 bool Properties::GetCompanyName(std::string* company_name) {
   if (!company_name) {
     LOGW("Properties::GetCompanyName: Invalid parameter");
@@ -139,4 +151,8 @@ bool Properties::GetOEMCryptoPath(std::string* library_name) {
   return true;
 }
 
+bool Properties::AlwaysUseKeySetIds() {
+  return false;
+}
+
 }  // namespace wvcdm