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/*
* Copyright (C) 2020 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.
*/
#include <attestation/HmacKeyManager.h>
#include <log/log.h>
#include <openssl/hmac.h>
#include <openssl/rand.h>
namespace android {
static std::array<uint8_t, 128> getRandomKey() {
std::array<uint8_t, 128> key;
if (RAND_bytes(key.data(), key.size()) != 1) {
LOG_ALWAYS_FATAL("Can't generate HMAC key");
}
return key;
}
HmacKeyManager::HmacKeyManager() : mHmacKey(getRandomKey()) {}
std::array<uint8_t, 32> HmacKeyManager::sign(const uint8_t* data, size_t size) const {
// SHA256 always generates 32-bytes result
std::array<uint8_t, 32> hash;
unsigned int hashLen = 0;
uint8_t* result =
HMAC(EVP_sha256(), mHmacKey.data(), mHmacKey.size(), data, size, hash.data(), &hashLen);
if (result == nullptr) {
ALOGE("Could not sign the data using HMAC");
return INVALID_HMAC;
}
if (hashLen != hash.size()) {
ALOGE("HMAC-SHA256 has unexpected length");
return INVALID_HMAC;
}
return hash;
}
} // namespace android
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