1 files changed, 52 insertions, 0 deletions
diff --git a/libs/attestation/HmacKeyManager.cpp b/libs/attestation/HmacKeyManager.cpp
new file mode 100644
index 0000000000..b15f143014
--- /dev/null
+++ b/libs/attestation/HmacKeyManager.cpp
@@ -0,0 +1,52 @@
+/*
+ * 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
+\ No newline at end of file