diff --git a/crypto/ext4crypt/KeyStorage4.h b/crypto/ext4crypt/KeyStorage4.h
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+/*
+ * Copyright (C) 2016 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.
+ */
+
+#ifndef ANDROID_TWRP_KEYSTORAGE_H
+#define ANDROID_TWRP_KEYSTORAGE_H
+
+#include "KeyBuffer.h"
+
+#include <string>
+
+namespace android {
+namespace vold {
+
+// Represents the information needed to decrypt a disk encryption key.
+// If "token" is nonempty, it is passed in as a required Gatekeeper auth token.
+// If "token" and "secret" are nonempty, "secret" is appended to the application-specific
+// binary needed to unlock.
+// If only "secret" is nonempty, it is used to decrypt in a non-Keymaster process.
+class KeyAuthentication {
+  public:
+    KeyAuthentication(std::string t, std::string s) : token{t}, secret{s} {};
+
+    bool usesKeymaster() const { return !token.empty() || secret.empty(); };
+
+    const std::string token;
+    const std::string secret;
+};
+
+extern const KeyAuthentication kEmptyAuthentication;
+
+// Checks if path "path" exists.
+bool pathExists(const std::string& path);
+
+bool createSecdiscardable(const std::string& path, std::string* hash);
+bool readSecdiscardable(const std::string& path, std::string* hash);
+
+// Create a directory at the named path, and store "key" in it,
+// in such a way that it can only be retrieved via Keymaster and
+// can be securely deleted.
+// It's safe to move/rename the directory after creation.
+bool storeKey(const std::string& dir, const KeyAuthentication& auth, const KeyBuffer& key);
+
+// Create a directory at the named path, and store "key" in it as storeKey
+// This version creates the key in "tmp_path" then atomically renames "tmp_path"
+// to "key_path" thereby ensuring that the key is either stored entirely or
+// not at all.
+bool storeKeyAtomically(const std::string& key_path, const std::string& tmp_path,
+                        const KeyAuthentication& auth, const KeyBuffer& key);
+
+// Retrieve the key from the named directory.
+bool retrieveKey(const std::string& dir, const KeyAuthentication& auth, KeyBuffer* key);
+
+// Securely destroy the key stored in the named directory and delete the directory.
+bool destroyKey(const std::string& dir);
+
+bool runSecdiscardSingle(const std::string& file);
+}  // namespace vold
+}  // namespace android
+
+#endif