/*
* 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 "ScryptParameters.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 <iostream>
#include <openssl/sha.h>
#include <android-base/file.h>
//#include <android-base/logging.h>
#include <cutils/properties.h>
#include <hardware/hw_auth_token.h>
#include <keymaster/authorization_set.h>
extern "C" {
#include "crypto_scrypt.h"
}
#define ERROR 1
#define LOG(x) std::cout
#define PLOG(x) std::cout
namespace android {
namespace vold {
const KeyAuthentication kEmptyAuthentication{"", ""};
static constexpr size_t AES_KEY_BYTES = 32;
static constexpr size_t GCM_NONCE_BYTES = 12;
static constexpr size_t GCM_MAC_BYTES = 16;
static constexpr size_t SALT_BYTES = 1 << 4;
static constexpr size_t SECDISCARDABLE_BYTES = 1 << 14;
static constexpr size_t STRETCHED_BYTES = 1 << 6;
static constexpr uint32_t AUTH_TIMEOUT = 30; // Seconds
static const char* kCurrentVersion = "1";
static const char* kRmPath = "/system/bin/rm";
static const char* kSecdiscardPath = "/system/bin/secdiscard";
static const char* kStretch_none = "none";
static const char* kStretch_nopassword = "nopassword";
static const std::string kStretchPrefix_scrypt = "scrypt ";
static const char* kFn_encrypted_key = "encrypted_key";
static const char* kFn_keymaster_key_blob = "keymaster_key_blob";
static const char* kFn_salt = "salt";
static const char* kFn_secdiscardable = "secdiscardable";
static const char* kFn_stretching = "stretching";
static const char* kFn_version = "version";
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 KeyAuthentication& auth,
const std::string& appId, std::string* key) {
auto paramBuilder = 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);
addStringParam(¶mBuilder, keymaster::TAG_APPLICATION_ID, appId);
if (auth.token.empty()) {
LOG(DEBUG) << "Creating key that doesn't need auth token";
paramBuilder.Authorization(keymaster::TAG_NO_AUTH_REQUIRED);
} else {
LOG(DEBUG) << "Auth token required for key";
if (auth.token.size() != sizeof(hw_auth_token_t)) {
LOG(ERROR) << "Auth token should be " << sizeof(hw_auth_token_t) << " bytes, was "
<< auth.token.size() << " bytes";
return false;
}
const hw_auth_token_t* at = reinterpret_cast<const hw_auth_token_t*>(auth.token.data());
paramBuilder.Authorization(keymaster::TAG_USER_SECURE_ID, at->user_id);
paramBuilder.Authorization(keymaster::TAG_USER_AUTH_TYPE, HW_AUTH_PASSWORD);
paramBuilder.Authorization(keymaster::TAG_AUTH_TIMEOUT, AUTH_TIMEOUT);
}
return keymaster.generateKey(paramBuilder.build(), key);
}*/
static keymaster::AuthorizationSetBuilder beginParams(const KeyAuthentication& auth,
const std::string& appId) {
auto paramBuilder = 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);
addStringParam(¶mBuilder, keymaster::TAG_APPLICATION_ID, appId);
if (!auth.token.empty()) {
LOG(DEBUG) << "Supplying auth token to Keymaster";
addStringParam(¶mBuilder, keymaster::TAG_AUTH_TOKEN, auth.token);
}
return paramBuilder;
}
/*static bool encryptWithKeymasterKey(Keymaster& keymaster, const std::string& key,
const KeyAuthentication& auth, const std::string& appId,
const std::string& message, std::string* ciphertext) {
auto params = beginParams(auth, appId).build();
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 KeyAuthentication& auth, const std::string& appId,
const std::string& ciphertext, std::string* message) {
auto nonce = ciphertext.substr(0, GCM_NONCE_BYTES);
auto bodyAndMac = ciphertext.substr(GCM_NONCE_BYTES);
auto params = addStringParam(beginParams(auth, appId), keymaster::TAG_NONCE, nonce).build();
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;
}*/
static std::string getStretching() {
char paramstr[PROPERTY_VALUE_MAX];
property_get(SCRYPT_PROP, paramstr, SCRYPT_DEFAULTS);
return std::string() + kStretchPrefix_scrypt + paramstr;
}
static bool stretchingNeedsSalt(const std::string& stretching) {
return stretching != kStretch_nopassword && stretching != kStretch_none;
}
static bool stretchSecret(const std::string& stretching, const std::string& secret,
const std::string& salt, std::string* stretched) {
if (stretching == kStretch_nopassword) {
if (!secret.empty()) {
LOG(WARNING) << "Password present but stretching is nopassword";
// Continue anyway
}
stretched->clear();
} else if (stretching == kStretch_none) {
*stretched = secret;
} else if (std::equal(kStretchPrefix_scrypt.begin(), kStretchPrefix_scrypt.end(),
stretching.begin())) {
int Nf, rf, pf;
if (!parse_scrypt_parameters(stretching.substr(kStretchPrefix_scrypt.size()).c_str(), &Nf,
&rf, &pf)) {
LOG(ERROR) << "Unable to parse scrypt params in stretching: " << stretching;
return false;
}
stretched->assign(STRETCHED_BYTES, '\0');
if (crypto_scrypt(reinterpret_cast<const uint8_t*>(secret.data()), secret.size(),
reinterpret_cast<const uint8_t*>(salt.data()), salt.size(),
1 << Nf, 1 << rf, 1 << pf,
reinterpret_cast<uint8_t*>(&(*stretched)[0]), stretched->size()) != 0) {
LOG(ERROR) << "scrypt failed with params: " << stretching;
return false;
}
} else {
LOG(ERROR) << "Unknown stretching type: " << stretching;
return false;
}
return true;
}
static bool generateAppId(const KeyAuthentication& auth, const std::string& stretching,
const std::string& salt, const std::string& secdiscardable,
std::string* appId) {
std::string stretched;
if (!stretchSecret(stretching, auth.secret, salt, &stretched)) return false;
*appId = hashSecdiscardable(secdiscardable) + stretched;
return true;
}
/*bool storeKey(const std::string& dir, const KeyAuthentication& auth, const std::string& key) {
if (TEMP_FAILURE_RETRY(mkdir(dir.c_str(), 0700)) == -1) {
PLOG(ERROR) << "key mkdir " << dir;
return false;
}
if (!writeStringToFile(kCurrentVersion, dir + "/" + kFn_version)) 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;
std::string stretching = auth.secret.empty() ? kStretch_nopassword : getStretching();
if (!writeStringToFile(stretching, dir + "/" + kFn_stretching)) return false;
std::string salt;
if (stretchingNeedsSalt(stretching)) {
if (ReadRandomBytes(SALT_BYTES, salt) != OK) {
LOG(ERROR) << "Random read failed";
return false;
}
if (!writeStringToFile(salt, dir + "/" + kFn_salt)) return false;
}
std::string appId;
if (!generateAppId(auth, stretching, salt, secdiscardable, &appId)) return false;
Keymaster keymaster;
if (!keymaster) return false;
std::string kmKey;
if (!generateKeymasterKey(keymaster, auth, appId, &kmKey)) return false;
if (!writeStringToFile(kmKey, dir + "/" + kFn_keymaster_key_blob)) return false;
std::string encryptedKey;
if (!encryptWithKeymasterKey(keymaster, kmKey, auth, appId, key, &encryptedKey)) return false;
if (!writeStringToFile(encryptedKey, dir + "/" + kFn_encrypted_key)) return false;
return true;
}*/
bool retrieveKey(const std::string& dir, const KeyAuthentication& auth, std::string* key) {
std::string version;
if (!readFileToString(dir + "/" + kFn_version, &version)) return false;
if (version != kCurrentVersion) {
LOG(ERROR) << "Version mismatch, expected " << kCurrentVersion << " got " << version;
return false;
}
std::string secdiscardable;
if (!readFileToString(dir + "/" + kFn_secdiscardable, &secdiscardable)) return false;
std::string stretching;
if (!readFileToString(dir + "/" + kFn_stretching, &stretching)) return false;
std::string salt;
if (stretchingNeedsSalt(stretching)) {
if (!readFileToString(dir + "/" + kFn_salt, &salt)) return false;
}
std::string appId;
if (!generateAppId(auth, stretching, salt, secdiscardable, &appId)) return false;
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, auth, appId, 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
