Add hadamard utilities to encode keys
Add the utility functions to encode & decode 32 bytes keys. The
hadamard encoding will expand a 2 bytes word to 2^15 bits. And thus the
32 byte key will expand to 64KiB in space. The encoded value is more
robust and we will be able to recover the key even if there is some
corruption.
Test: unittest pass
Change-Id: Iae8a28a8c7c1699f8641f9250f0eccde5c2ff138
diff --git a/rebootescrow/aidl/default/HadamardUtils.h b/rebootescrow/aidl/default/HadamardUtils.h
new file mode 100644
index 0000000..21cfc78
--- /dev/null
+++ b/rebootescrow/aidl/default/HadamardUtils.h
@@ -0,0 +1,62 @@
+/*
+ * 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