Decrypt FBE on 9.0 (backwards compatible)

Building in 9.0 may require you to add a flag to your twrp fstab
with the fileencryption details like:
fileencryption=ice:aes-256-heh

Verify this against your device's stock fstab of course.

Change-Id: If9286f5d5787280814daca9fbc8f5191ff26a839
diff --git a/crypto/ext4crypt/KeyUtil.h b/crypto/ext4crypt/KeyUtil.h
new file mode 100644
index 0000000..d5ad69f
--- /dev/null
+++ b/crypto/ext4crypt/KeyUtil.h
@@ -0,0 +1,41 @@
+/*
+ * 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_VOLD_KEYUTIL_H
+#define ANDROID_VOLD_KEYUTIL_H
+
+#include "KeyBuffer.h"
+#include "KeyStorage4.h"
+
+#include <string>
+#include <memory>
+
+namespace android {
+namespace vold {
+
+bool randomKey(KeyBuffer* key);
+bool installKey(const KeyBuffer& key, std::string* raw_ref);
+bool evictKey(const std::string& raw_ref);
+bool retrieveAndInstallKey(bool create_if_absent, const KeyAuthentication& key_authentication,
+                           const std::string& key_path, const std::string& tmp_path,
+                           std::string* key_ref);
+bool retrieveKey(bool create_if_absent, const std::string& key_path,
+                 const std::string& tmp_path, KeyBuffer* key);
+
+}  // namespace vold
+}  // namespace android
+
+#endif