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/*
* 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.
*/
#include "KeyStorage.h"
#include "Keymaster.h"
#include "Utils.h"
#include <vector>
#include <errno.h>
#include <sys/stat.h>
#include <sys/types.h>
#include <sys/wait.h>
#include <unistd.h>
#include <openssl/sha.h>
#include <android-base/file.h>
#include <android-base/logging.h>
#include <keymaster/authorization_set.h>
namespace android {
namespace vold {
static constexpr size_t AES_KEY_BYTES = 32;
static constexpr size_t GCM_NONCE_BYTES = 12;
static constexpr size_t GCM_MAC_BYTES = 16;
// FIXME: better name than "secdiscardable" sought!
static constexpr size_t SECDISCARDABLE_BYTES = 1<<14;
static const char* kRmPath = "/system/bin/rm";
static const char* kSecdiscardPath = "/system/bin/secdiscard";
static const char* kFn_keymaster_key_blob = "keymaster_key_blob";
static const char* kFn_encrypted_key = "encrypted_key";
static const char* kFn_secdiscardable = "secdiscardable";
static bool checkSize(const std::string& kind, size_t actual, size_t expected) {
if (actual != expected) {
LOG(ERROR) << "Wrong number of bytes in " << kind << ", expected " << expected
<< " got " << actual;
return false;
}
return true;
}
static std::string hashSecdiscardable(const std::string &secdiscardable) {
SHA512_CTX c;
SHA512_Init(&c);
// Personalise the hashing by introducing a fixed prefix.
// Hashing applications should use personalization except when there is a
// specific reason not to; see section 4.11 of https://www.schneier.com/skein1.3.pdf
std::string secdiscardableHashingPrefix = "Android secdiscardable SHA512";
secdiscardableHashingPrefix.resize(SHA512_CBLOCK);
SHA512_Update(&c, secdiscardableHashingPrefix.data(), secdiscardableHashingPrefix.size());
SHA512_Update(&c, secdiscardable.data(), secdiscardable.size());
std::string res(SHA512_DIGEST_LENGTH, '\0');
SHA512_Final(reinterpret_cast<uint8_t *>(&res[0]), &c);
return res;
}
static bool generateKeymasterKey(Keymaster &keymaster,
const keymaster::AuthorizationSet &extraParams,
std::string &key) {
auto params = keymaster::AuthorizationSetBuilder()
.AesEncryptionKey(AES_KEY_BYTES * 8)
.Authorization(keymaster::TAG_BLOCK_MODE, KM_MODE_GCM)
.Authorization(keymaster::TAG_MIN_MAC_LENGTH, GCM_MAC_BYTES * 8)
.Authorization(keymaster::TAG_PADDING, KM_PAD_NONE)
.Authorization(keymaster::TAG_NO_AUTH_REQUIRED) // FIXME integrate with gatekeeper
.build();
params.push_back(extraParams);
return keymaster.generateKey(params, key);
}
static bool encryptWithKeymasterKey(
Keymaster &keymaster,
const std::string &key,
const keymaster::AuthorizationSet &extraParams,
const std::string &message,
std::string &ciphertext) {
// FIXME fix repetition
auto params = keymaster::AuthorizationSetBuilder()
.Authorization(keymaster::TAG_BLOCK_MODE, KM_MODE_GCM)
.Authorization(keymaster::TAG_MAC_LENGTH, GCM_MAC_BYTES * 8)
.Authorization(keymaster::TAG_PADDING, KM_PAD_NONE)
.build();
params.push_back(extraParams);
keymaster::AuthorizationSet outParams;
auto opHandle = keymaster.begin(KM_PURPOSE_ENCRYPT, key, params, outParams);
if (!opHandle) return false;
keymaster_blob_t nonceBlob;
if (!outParams.GetTagValue(keymaster::TAG_NONCE, &nonceBlob)) {
LOG(ERROR) << "GCM encryption but no nonce generated";
return false;
}
// nonceBlob here is just a pointer into existing data, must not be freed
std::string nonce(reinterpret_cast<const char *>(nonceBlob.data), nonceBlob.data_length);
if (!checkSize("nonce", nonce.size(), GCM_NONCE_BYTES)) return false;
std::string body;
if (!opHandle.updateCompletely(message, body)) return false;
std::string mac;
if (!opHandle.finishWithOutput(mac)) return false;
if (!checkSize("mac", mac.size(), GCM_MAC_BYTES)) return false;
ciphertext = nonce + body + mac;
return true;
}
static bool decryptWithKeymasterKey(
Keymaster &keymaster, const std::string &key,
const keymaster::AuthorizationSet &extraParams,
const std::string &ciphertext,
std::string &message) {
auto nonce = ciphertext.substr(0, GCM_NONCE_BYTES);
auto bodyAndMac = ciphertext.substr(GCM_NONCE_BYTES);
// FIXME fix repetition
auto params = addStringParam(keymaster::AuthorizationSetBuilder(), keymaster::TAG_NONCE, nonce)
.Authorization(keymaster::TAG_BLOCK_MODE, KM_MODE_GCM)
.Authorization(keymaster::TAG_MAC_LENGTH, GCM_MAC_BYTES * 8)
.Authorization(keymaster::TAG_PADDING, KM_PAD_NONE)
.build();
params.push_back(extraParams);
auto opHandle = keymaster.begin(KM_PURPOSE_DECRYPT, key, params);
if (!opHandle) return false;
if (!opHandle.updateCompletely(bodyAndMac, message)) return false;
if (!opHandle.finish()) return false;
return true;
}
static bool readFileToString(const std::string &filename, std::string &result) {
if (!android::base::ReadFileToString(filename, &result)) {
PLOG(ERROR) << "Failed to read from " << filename;
return false;
}
return true;
}
static bool writeStringToFile(const std::string &payload, const std::string &filename) {
if (!android::base::WriteStringToFile(payload, filename)) {
PLOG(ERROR) << "Failed to write to " << filename;
return false;
}
return true;
}
bool storeKey(const std::string &dir, const std::string &key) {
if (TEMP_FAILURE_RETRY(mkdir(dir.c_str(), 0700)) == -1) {
PLOG(ERROR) << "key mkdir " << dir;
return false;
}
std::string secdiscardable;
if (ReadRandomBytes(SECDISCARDABLE_BYTES, secdiscardable) != OK) {
// TODO status_t plays badly with PLOG, fix it.
LOG(ERROR) << "Random read failed";
return false;
}
if (!writeStringToFile(secdiscardable, dir + "/" + kFn_secdiscardable)) return false;
auto extraParams = addStringParam(keymaster::AuthorizationSetBuilder(),
keymaster::TAG_APPLICATION_ID, hashSecdiscardable(secdiscardable)).build();
Keymaster keymaster;
if (!keymaster) return false;
std::string kmKey;
if (!generateKeymasterKey(keymaster, extraParams, kmKey)) return false;
std::string encryptedKey;
if (!encryptWithKeymasterKey(
keymaster, kmKey, extraParams, key, encryptedKey)) return false;
if (!writeStringToFile(kmKey, dir + "/" + kFn_keymaster_key_blob)) return false;
if (!writeStringToFile(encryptedKey, dir + "/" + kFn_encrypted_key)) return false;
return true;
}
bool retrieveKey(const std::string &dir, std::string &key) {
std::string secdiscardable;
if (!readFileToString(dir + "/" + kFn_secdiscardable, secdiscardable)) return false;
auto extraParams = addStringParam(keymaster::AuthorizationSetBuilder(),
keymaster::TAG_APPLICATION_ID, hashSecdiscardable(secdiscardable)).build();
std::string kmKey;
if (!readFileToString(dir + "/" + kFn_keymaster_key_blob, kmKey)) return false;
std::string encryptedMessage;
if (!readFileToString(dir + "/" + kFn_encrypted_key, encryptedMessage)) return false;
Keymaster keymaster;
if (!keymaster) return false;
return decryptWithKeymasterKey(keymaster, kmKey, extraParams, encryptedMessage, key);
}
static bool deleteKey(const std::string &dir) {
std::string kmKey;
if (!readFileToString(dir + "/" + kFn_keymaster_key_blob, kmKey)) return false;
Keymaster keymaster;
if (!keymaster) return false;
if (!keymaster.deleteKey(kmKey)) return false;
return true;
}
static bool secdiscardSecdiscardable(const std::string &dir) {
if (ForkExecvp(std::vector<std::string> {
kSecdiscardPath, "--", dir + "/" + kFn_secdiscardable}) != 0) {
LOG(ERROR) << "secdiscard failed";
return false;
}
return true;
}
static bool recursiveDeleteKey(const std::string &dir) {
if (ForkExecvp(std::vector<std::string> {
kRmPath, "-rf", dir}) != 0) {
LOG(ERROR) << "recursive delete failed";
return false;
}
return true;
}
bool destroyKey(const std::string &dir) {
bool success = true;
// Try each thing, even if previous things failed.
success &= deleteKey(dir);
success &= secdiscardSecdiscardable(dir);
success &= recursiveDeleteKey(dir);
return success;
}
} // namespace vold
} // namespace android