diff --git a/rebootescrow/aidl/default/HadamardUtils.h b/rebootescrow/aidl/default/HadamardUtils.h
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+++ b/rebootescrow/aidl/default/HadamardUtils.h
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+/*
+ * Copyright (C) 2019 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.
+ */
+
+#pragma once
+
+#include <stdint.h>
+
+#include <bitset>
+#include <queue>
+#include <utility>
+#include <vector>
+
+namespace aidl {
+namespace android {
+namespace hardware {
+namespace rebootescrow {
+namespace hadamard {
+
+constexpr uint32_t CODE_K = 15;
+constexpr uint32_t ENCODE_LENGTH = 1u << CODE_K;
+constexpr auto KEY_SIZE_IN_BYTES = 32u;
+
+// Encodes a 2 bytes word with hadamard code. The encoding expands a word of k+1 bits to a 2^k
+// bitset. Returns the encoded bitset.
+std::bitset<ENCODE_LENGTH> EncodeWord(uint16_t word);
+
+// Decodes the input bitset, and returns a sorted list of pair with (score, value). The value with
+// a higher score indicates a greater likehood.
+std::priority_queue<std::pair<int32_t, uint16_t>> DecodeWord(
+        const std::bitset<ENCODE_LENGTH>& encoded);
+
+// Encodes a key that has a size of KEY_SIZE_IN_BYTES. Returns a byte array representation of the
+// encoded bitset. So a 32 bytes key will expand to 16*(2^15) bits = 64KiB.
+std::vector<uint8_t> EncodeKey(const std::vector<uint8_t>& input);
+
+// Given a byte array representation of the encoded keys, decodes it and return the result.
+std::vector<uint8_t> DecodeKey(const std::vector<uint8_t>& encoded);
+
+// Converts a bitset of length |ENCODE_LENGTH| to a byte array.
+std::vector<uint8_t> BitsetToBytes(const std::bitset<ENCODE_LENGTH>& encoded_bits);
+
+// Converts a byte array of encoded words back to the bitset.
+std::bitset<ENCODE_LENGTH> BytesToBitset(const std::vector<uint8_t>& encoded);
+
+}  // namespace hadamard
+}  // namespace rebootescrow
+}  // namespace hardware
+}  // namespace android
+}  // namespace aidl