diff --git a/libwvdrmengine/cdm/core/include/device_files.h b/libwvdrmengine/cdm/core/include/device_files.h
index d8265726..3d02be74 100644
--- a/libwvdrmengine/cdm/core/include/device_files.h
+++ b/libwvdrmengine/cdm/core/include/device_files.h
@@ -85,12 +85,15 @@ class DeviceFiles {
  private:
   // Helpers that wrap the File interface and automatically handle hashing, as
   // well as adding the device files base path to to the file name.
-  bool StoreFileWithHash(const char* name, const std::string& serialized_file);
-  bool StoreFileRaw(const char* name, const std::string& serialized_file);
-  bool RetrieveHashedFile(const char* name, std::string* serialized_file);
-  bool FileExists(const char* name);
-  bool RemoveFile(const char* name);
-  ssize_t GetFileSize(const char* name);
+  bool StoreFileWithHash(const std::string& name,
+                         const std::string& serialized_file);
+  bool StoreFileRaw(const std::string& name,
+                    const std::string& serialized_file);
+  bool RetrieveHashedFile(const std::string& name,
+                          std::string* serialized_file);
+  bool FileExists(const std::string& name);
+  bool RemoveFile(const std::string& name);
+  ssize_t GetFileSize(const std::string& name);
 
   // Certificate and offline licenses are now stored in security
   // level specific directories. In an earlier version they were
diff --git a/libwvdrmengine/cdm/core/src/device_files.cpp b/libwvdrmengine/cdm/core/src/device_files.cpp
index 81059eab..def9ddee 100644
--- a/libwvdrmengine/cdm/core/src/device_files.cpp
+++ b/libwvdrmengine/cdm/core/src/device_files.cpp
@@ -197,8 +197,7 @@ bool DeviceFiles::StoreLicense(const std::string& key_set_id,
   std::string serialized_file;
   file.SerializeToString(&serialized_file);
 
-  std::string file_name = key_set_id + kLicenseFileNameExt;
-  return StoreFileWithHash(file_name.c_str(), serialized_file);
+  return StoreFileWithHash(key_set_id + kLicenseFileNameExt, serialized_file);
 }
 
 bool DeviceFiles::RetrieveLicense(
@@ -213,8 +212,9 @@ bool DeviceFiles::RetrieveLicense(
   }
 
   std::string serialized_file;
-  std::string file_name = key_set_id + kLicenseFileNameExt;
-  if (!RetrieveHashedFile(file_name.c_str(), &serialized_file)) return false;
+  if (!RetrieveHashedFile(key_set_id + kLicenseFileNameExt, &serialized_file)) {
+    return false;
+  }
 
   video_widevine_client::sdk::File file;
   if (!file.ParseFromString(serialized_file)) {
@@ -268,10 +268,7 @@ bool DeviceFiles::DeleteLicense(const std::string& key_set_id) {
     LOGW("DeviceFiles::DeleteLicense: not initialized");
     return false;
   }
-
-  std::string file_name(key_set_id);
-  file_name.append(kLicenseFileNameExt);
-  return RemoveFile(file_name.c_str());
+  return RemoveFile(key_set_id + kLicenseFileNameExt);
 }
 
 bool DeviceFiles::DeleteAllLicenses() {
@@ -279,10 +276,7 @@ bool DeviceFiles::DeleteAllLicenses() {
     LOGW("DeviceFiles::DeleteAllLicenses: not initialized");
     return false;
   }
-
-  std::string file_name(kWildcard);
-  file_name.append(kLicenseFileNameExt);
-  return RemoveFile(file_name.c_str());
+  return RemoveFile(std::string(kWildcard) + kLicenseFileNameExt);
 }
 
 bool DeviceFiles::DeleteAllFiles() {
@@ -301,10 +295,7 @@ bool DeviceFiles::LicenseExists(const std::string& key_set_id) {
     LOGW("DeviceFiles::LicenseExists: not initialized");
     return false;
   }
-
-  std::string file_name(key_set_id);
-  file_name.append(kLicenseFileNameExt);
-  return FileExists(file_name.c_str());
+  return FileExists(key_set_id + kLicenseFileNameExt);
 }
 
 bool DeviceFiles::ReserveLicenseId(const std::string& key_set_id) {
@@ -312,9 +303,7 @@ bool DeviceFiles::ReserveLicenseId(const std::string& key_set_id) {
     LOGW("DeviceFiles::ReserveLicenseId: not initialized");
     return false;
   }
-
-  std::string file_name = key_set_id + kLicenseFileNameExt;
-  return StoreFileRaw(file_name.c_str(), kBlankFileData);
+  return StoreFileRaw(key_set_id + kLicenseFileNameExt, kBlankFileData);
 }
 
 bool DeviceFiles::StoreUsageInfo(const std::string& provider_session_token,
@@ -329,7 +318,7 @@ bool DeviceFiles::StoreUsageInfo(const std::string& provider_session_token,
   std::string serialized_file;
   video_widevine_client::sdk::File file;
   std::string file_name = GetUsageInfoFileName(app_id);
-  if (!RetrieveHashedFile(file_name.c_str(), &serialized_file)) {
+  if (!RetrieveHashedFile(file_name, &serialized_file)) {
     file.set_type(video_widevine_client::sdk::File::USAGE_INFO);
     file.set_version(video_widevine_client::sdk::File::VERSION_1);
   } else {
@@ -348,7 +337,7 @@ bool DeviceFiles::StoreUsageInfo(const std::string& provider_session_token,
   provider_session->set_license(key_response.data(), key_response.size());
 
   file.SerializeToString(&serialized_file);
-  return StoreFileWithHash(file_name.c_str(), serialized_file);
+  return StoreFileWithHash(file_name, serialized_file);
 }
 
 bool DeviceFiles::DeleteUsageInfo(const std::string& app_id,
@@ -359,7 +348,7 @@ bool DeviceFiles::DeleteUsageInfo(const std::string& app_id,
   }
   std::string serialized_file;
   std::string file_name = GetUsageInfoFileName(app_id);
-  if (!RetrieveHashedFile(file_name.c_str(), &serialized_file)) return false;
+  if (!RetrieveHashedFile(file_name, &serialized_file)) return false;
 
   video_widevine_client::sdk::File file;
   if (!file.ParseFromString(serialized_file)) {
@@ -393,7 +382,7 @@ bool DeviceFiles::DeleteUsageInfo(const std::string& app_id,
   sessions->RemoveLast();
 
   file.SerializeToString(&serialized_file);
-  return StoreFileWithHash(file_name.c_str(), serialized_file);
+  return StoreFileWithHash(file_name, serialized_file);
 }
 
 bool DeviceFiles::DeleteAllUsageInfoForApp(
@@ -410,9 +399,9 @@ bool DeviceFiles::DeleteAllUsageInfoForApp(
   provider_session_tokens->clear();
 
   std::string file_name = GetUsageInfoFileName(app_id);
-  if (!FileExists(file_name.c_str())) return true;
+  if (!FileExists(file_name)) return true;
   std::string serialized_file;
-  if (RetrieveHashedFile(file_name.c_str(), &serialized_file)) {
+  if (RetrieveHashedFile(file_name, &serialized_file)) {
     video_widevine_client::sdk::File file_proto;
     if (!file_proto.ParseFromString(serialized_file)) {
       LOGW("DeviceFiles::DeleteAllUsageInfoForApp: Unable to parse file");
@@ -425,7 +414,7 @@ bool DeviceFiles::DeleteAllUsageInfoForApp(
   } else {
     LOGW("DeviceFiles::DeleteAllUsageInfoForApp: Unable to retrieve file");
   }
-  return RemoveFile(file_name.c_str());
+  return RemoveFile(file_name);
 }
 
 bool DeviceFiles::RetrieveUsageInfo(
@@ -445,8 +434,8 @@ bool DeviceFiles::RetrieveUsageInfo(
 
   std::string serialized_file;
   std::string file_name = GetUsageInfoFileName(app_id);
-  if (!RetrieveHashedFile(file_name.c_str(), &serialized_file)) {
-    if (!FileExists(file_name.c_str()) || GetFileSize(file_name.c_str()) == 0) {
+  if (!RetrieveHashedFile(file_name, &serialized_file)) {
+    if (!FileExists(file_name) || GetFileSize(file_name) == 0) {
       usage_info->resize(0);
       return true;
     }
@@ -480,7 +469,7 @@ bool DeviceFiles::RetrieveUsageInfo(const std::string& app_id,
   }
   std::string serialized_file;
   std::string file_name = GetUsageInfoFileName(app_id);
-  if (!RetrieveHashedFile(file_name.c_str(), &serialized_file)) return false;
+  if (!RetrieveHashedFile(file_name, &serialized_file)) return false;
 
   video_widevine_client::sdk::File file;
   if (!file.ParseFromString(serialized_file)) {
@@ -505,18 +494,13 @@ bool DeviceFiles::RetrieveUsageInfo(const std::string& app_id,
   return true;
 }
 
-bool DeviceFiles::StoreFileWithHash(const char* name,
+bool DeviceFiles::StoreFileWithHash(const std::string& name,
                                     const std::string& serialized_file) {
   if (!file_.get()) {
     LOGW("DeviceFiles::StoreFileWithHash: Invalid file handle");
     return false;
   }
 
-  if (!name) {
-    LOGW("DeviceFiles::StoreFileWithHash: Unspecified file name parameter");
-    return false;
-  }
-
   // calculate SHA hash
   std::string hash;
   if (!Hash(serialized_file, &hash)) {
@@ -535,18 +519,13 @@ bool DeviceFiles::StoreFileWithHash(const char* name,
   return StoreFileRaw(name, serialized_hash_file);
 }
 
-bool DeviceFiles::StoreFileRaw(const char* name,
+bool DeviceFiles::StoreFileRaw(const std::string& name,
                                const std::string& serialized_file) {
   if (!file_.get()) {
     LOGW("DeviceFiles::StoreFileRaw: Invalid file handle");
     return false;
   }
 
-  if (!name) {
-    LOGW("DeviceFiles::StoreFileRaw: Unspecified file name parameter");
-    return false;
-  }
-
   std::string path;
   if (!Properties::GetDeviceFilesBasePath(security_level_, &path)) {
     LOGW("DeviceFiles::StoreFileRaw: Unable to get base path");
@@ -580,18 +559,13 @@ bool DeviceFiles::StoreFileRaw(const char* name,
   return true;
 }
 
-bool DeviceFiles::RetrieveHashedFile(const char* name,
+bool DeviceFiles::RetrieveHashedFile(const std::string& name,
                                      std::string* serialized_file) {
   if (!file_.get()) {
     LOGW("DeviceFiles::RetrieveHashedFile: Invalid file handle");
     return false;
   }
 
-  if (!name) {
-    LOGW("DeviceFiles::RetrieveHashedFile: Unspecified file name parameter");
-    return false;
-  }
-
   if (!serialized_file) {
     LOGW(
         "DeviceFiles::RetrieveHashedFile: Unspecified serialized_file "
@@ -663,17 +637,12 @@ bool DeviceFiles::RetrieveHashedFile(const char* name,
   return true;
 }
 
-bool DeviceFiles::FileExists(const char* name) {
+bool DeviceFiles::FileExists(const std::string& name) {
   if (!file_.get()) {
     LOGW("DeviceFiles::FileExists: Invalid file handle");
     return false;
   }
 
-  if (!name) {
-    LOGW("DeviceFiles::FileExists: Unspecified file name parameter");
-    return false;
-  }
-
   std::string path;
   if (!Properties::GetDeviceFilesBasePath(security_level_, &path)) {
     LOGW("DeviceFiles::FileExists: Unable to get base path");
@@ -684,17 +653,12 @@ bool DeviceFiles::FileExists(const char* name) {
   return file_->Exists(path);
 }
 
-bool DeviceFiles::RemoveFile(const char* name) {
+bool DeviceFiles::RemoveFile(const std::string& name) {
   if (!file_.get()) {
     LOGW("DeviceFiles::RemoveFile: Invalid file handle");
     return false;
   }
 
-  if (!name) {
-    LOGW("DeviceFiles::RemoveFile: Unspecified file name parameter");
-    return false;
-  }
-
   std::string path;
   if (!Properties::GetDeviceFilesBasePath(security_level_, &path)) {
     LOGW("DeviceFiles::RemoveFile: Unable to get base path");
@@ -705,17 +669,12 @@ bool DeviceFiles::RemoveFile(const char* name) {
   return file_->Remove(path);
 }
 
-ssize_t DeviceFiles::GetFileSize(const char* name) {
+ssize_t DeviceFiles::GetFileSize(const std::string& name) {
   if (!file_.get()) {
     LOGW("DeviceFiles::GetFileSize: Invalid file handle");
     return -1;
   }
 
-  if (!name) {
-    LOGW("DeviceFiles::GetFileSize: Unspecified file name parameter");
-    return -1;
-  }
-
   std::string path;
   if (!Properties::GetDeviceFilesBasePath(security_level_, &path)) {
     LOGW("DeviceFiles::GetFileSize: Unable to get base path");