KeyStorage.cpp - SHIFTPHONES/android_system_vold - Gitiles

 /*
  * 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 secdiscardable_hashing_prefix = "Android secdiscardable SHA512";
     secdiscardable_hashing_prefix.resize(SHA512_CBLOCK);
     SHA512_Update(&c, secdiscardable_hashing_prefix.data(), secdiscardable_hashing_prefix.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 &extra_params,
         std::string &key) {
     keymaster::AuthorizationSetBuilder param_builder;
     param_builder
         .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
     auto params = param_builder.build();
     params.push_back(extra_params);
     return keymaster.GenerateKey(params, key);
 }

 static bool EncryptWithKeymasterKey(
         Keymaster &keymaster,
         const std::string &key,
         const keymaster::AuthorizationSet &extra_params,
         const std::string &message,
         std::string &ciphertext) {
     // FIXME fix repetition
     keymaster::AuthorizationSetBuilder param_builder;
     param_builder
         .Authorization(keymaster::TAG_BLOCK_MODE, KM_MODE_GCM)
         .Authorization(keymaster::TAG_MAC_LENGTH, GCM_MAC_BYTES * 8)
         .Authorization(keymaster::TAG_PADDING, KM_PAD_NONE);
     auto params = param_builder.build();
     params.push_back(extra_params);
     keymaster::AuthorizationSet out_params;
     auto op_handle = keymaster.Begin(KM_PURPOSE_ENCRYPT, key, params, out_params);
     if (!op_handle) return false;
     keymaster_blob_t nonce_blob;
     if (!out_params.GetTagValue(keymaster::TAG_NONCE, &nonce_blob)) {
         LOG(ERROR) << "GCM encryption but no nonce generated";
         return false;
     }
     // nonce_blob here is just a pointer into existing data, must not be freed
     std::string nonce(reinterpret_cast<const char *>(nonce_blob.data), nonce_blob.data_length);
     if (!CheckSize("nonce", nonce.size(), GCM_NONCE_BYTES)) return false;
     std::string body;
     if (!op_handle.UpdateCompletely(message, body)) return false;

     std::string mac;
     if (!op_handle.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 &extra_params,
         const std::string &ciphertext,
         std::string &message) {
     auto nonce = ciphertext.substr(0, GCM_NONCE_BYTES);
     auto body_mac = ciphertext.substr(GCM_NONCE_BYTES);
     // FIXME fix repetition
     keymaster::AuthorizationSetBuilder param_builder;
     param_builder
         .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(param_builder, keymaster::TAG_NONCE, nonce);
     auto params = param_builder.build();
     params.push_back(extra_params);

     auto op_handle = keymaster.Begin(KM_PURPOSE_DECRYPT, key, params);
     if (!op_handle) return false;
     if (!op_handle.UpdateCompletely(body_mac, message)) return false;
     if (!op_handle.Finish()) 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) != 0) {
         // TODO status_t plays badly with PLOG, fix it.
         LOG(ERROR) << "Random read failed";
         return false;
     }
     // FIXME create a wrapper around reads and writes which handles error logging
     if (!android::base::WriteStringToFile(secdiscardable, dir + "/" + kFn_secdiscardable)) {
          PLOG(ERROR) << "Unable to write secdiscardable to " << dir;
          return false;
     }
     keymaster::AuthorizationSetBuilder param_builder;
     AddStringParam(param_builder, keymaster::TAG_APPLICATION_ID,
         HashSecdiscardable(secdiscardable));
     auto extra_params = param_builder.build();
     Keymaster keymaster;
     if (!keymaster) return false;
     std::string km_key;
     if (!GenerateKeymasterKey(keymaster, extra_params, km_key)) return false;
     std::string encrypted_key;
     if (!EncryptWithKeymasterKey(
         keymaster, km_key, extra_params, key, encrypted_key)) return false;
     if (!android::base::WriteStringToFile(km_key, dir + "/" + kFn_keymaster_key_blob)) {
         PLOG(ERROR) << "Unable to write keymaster_key_blob to " << dir;
         return false;
     }
     if (!android::base::WriteStringToFile(encrypted_key, dir + "/" + kFn_encrypted_key)) {
         PLOG(ERROR) << "Unable to write encrypted_key to " << dir;
         return false;
     }
     return true;
 }

 bool RetrieveKey(const std::string &dir, std::string &key) {
     std::string secdiscardable;
     if (!android::base::ReadFileToString(dir + "/" + kFn_secdiscardable, &secdiscardable)) {
          PLOG(ERROR) << "Unable to read secdiscardable from " << dir;
          return false;
     }
     keymaster::AuthorizationSetBuilder param_builder;
     AddStringParam(param_builder, keymaster::TAG_APPLICATION_ID,
         HashSecdiscardable(secdiscardable));
     auto extra_params = param_builder.build();
     std::string km_key;
     if (!android::base::ReadFileToString(dir + "/" + kFn_keymaster_key_blob, &km_key)) {
          PLOG(ERROR) << "Unable to read keymaster_key_blob from " << dir;
          return false;
     }
     std::string encrypted_message;
     if (!android::base::ReadFileToString(dir + "/" + kFn_encrypted_key, &encrypted_message)) {
          PLOG(ERROR) << "Unable to read encrypted_key to " << dir;
          return false;
     }
     Keymaster keymaster;
     if (!keymaster) return false;
     return DecryptWithKeymasterKey(keymaster, km_key, extra_params, encrypted_message, key);
 }

 static bool DeleteKey(const std::string &dir) {
     std::string km_key;
     if (!android::base::ReadFileToString(dir + "/" + kFn_keymaster_key_blob, &km_key)) {
          PLOG(ERROR) << "Unable to read keymaster_key_blob from " << dir;
          return false;
     }
     Keymaster keymaster;
     if (!keymaster) return false;
     if (!keymaster.DeleteKey(km_key)) 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
	/*
	* 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 secdiscardable_hashing_prefix = "Android secdiscardable SHA512";
	secdiscardable_hashing_prefix.resize(SHA512_CBLOCK);
	SHA512_Update(&c, secdiscardable_hashing_prefix.data(), secdiscardable_hashing_prefix.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 &extra_params,
	std::string &key) {
	keymaster::AuthorizationSetBuilder param_builder;
	param_builder
	.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
	auto params = param_builder.build();
	params.push_back(extra_params);
	return keymaster.GenerateKey(params, key);
	}

	static bool EncryptWithKeymasterKey(
	Keymaster &keymaster,
	const std::string &key,
	const keymaster::AuthorizationSet &extra_params,
	const std::string &message,
	std::string &ciphertext) {
	// FIXME fix repetition
	keymaster::AuthorizationSetBuilder param_builder;
	param_builder
	.Authorization(keymaster::TAG_BLOCK_MODE, KM_MODE_GCM)
	.Authorization(keymaster::TAG_MAC_LENGTH, GCM_MAC_BYTES * 8)
	.Authorization(keymaster::TAG_PADDING, KM_PAD_NONE);
	auto params = param_builder.build();
	params.push_back(extra_params);
	keymaster::AuthorizationSet out_params;
	auto op_handle = keymaster.Begin(KM_PURPOSE_ENCRYPT, key, params, out_params);
	if (!op_handle) return false;
	keymaster_blob_t nonce_blob;
	if (!out_params.GetTagValue(keymaster::TAG_NONCE, &nonce_blob)) {
	LOG(ERROR) << "GCM encryption but no nonce generated";
	return false;
	}
	// nonce_blob here is just a pointer into existing data, must not be freed
	std::string nonce(reinterpret_cast<const char *>(nonce_blob.data), nonce_blob.data_length);
	if (!CheckSize("nonce", nonce.size(), GCM_NONCE_BYTES)) return false;
	std::string body;
	if (!op_handle.UpdateCompletely(message, body)) return false;

	std::string mac;
	if (!op_handle.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 &extra_params,
	const std::string &ciphertext,
	std::string &message) {
	auto nonce = ciphertext.substr(0, GCM_NONCE_BYTES);
	auto body_mac = ciphertext.substr(GCM_NONCE_BYTES);
	// FIXME fix repetition
	keymaster::AuthorizationSetBuilder param_builder;
	param_builder
	.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(param_builder, keymaster::TAG_NONCE, nonce);
	auto params = param_builder.build();
	params.push_back(extra_params);

	auto op_handle = keymaster.Begin(KM_PURPOSE_DECRYPT, key, params);
	if (!op_handle) return false;
	if (!op_handle.UpdateCompletely(body_mac, message)) return false;
	if (!op_handle.Finish()) 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) != 0) {
	// TODO status_t plays badly with PLOG, fix it.
	LOG(ERROR) << "Random read failed";
	return false;
	}
	// FIXME create a wrapper around reads and writes which handles error logging
	if (!android::base::WriteStringToFile(secdiscardable, dir + "/" + kFn_secdiscardable)) {
	PLOG(ERROR) << "Unable to write secdiscardable to " << dir;
	return false;
	}
	keymaster::AuthorizationSetBuilder param_builder;
	AddStringParam(param_builder, keymaster::TAG_APPLICATION_ID,
	HashSecdiscardable(secdiscardable));
	auto extra_params = param_builder.build();
	Keymaster keymaster;
	if (!keymaster) return false;
	std::string km_key;
	if (!GenerateKeymasterKey(keymaster, extra_params, km_key)) return false;
	std::string encrypted_key;
	if (!EncryptWithKeymasterKey(
	keymaster, km_key, extra_params, key, encrypted_key)) return false;
	if (!android::base::WriteStringToFile(km_key, dir + "/" + kFn_keymaster_key_blob)) {
	PLOG(ERROR) << "Unable to write keymaster_key_blob to " << dir;
	return false;
	}
	if (!android::base::WriteStringToFile(encrypted_key, dir + "/" + kFn_encrypted_key)) {
	PLOG(ERROR) << "Unable to write encrypted_key to " << dir;
	return false;
	}
	return true;
	}

	bool RetrieveKey(const std::string &dir, std::string &key) {
	std::string secdiscardable;
	if (!android::base::ReadFileToString(dir + "/" + kFn_secdiscardable, &secdiscardable)) {
	PLOG(ERROR) << "Unable to read secdiscardable from " << dir;
	return false;
	}
	keymaster::AuthorizationSetBuilder param_builder;
	AddStringParam(param_builder, keymaster::TAG_APPLICATION_ID,
	HashSecdiscardable(secdiscardable));
	auto extra_params = param_builder.build();
	std::string km_key;
	if (!android::base::ReadFileToString(dir + "/" + kFn_keymaster_key_blob, &km_key)) {
	PLOG(ERROR) << "Unable to read keymaster_key_blob from " << dir;
	return false;
	}
	std::string encrypted_message;
	if (!android::base::ReadFileToString(dir + "/" + kFn_encrypted_key, &encrypted_message)) {
	PLOG(ERROR) << "Unable to read encrypted_key to " << dir;
	return false;
	}
	Keymaster keymaster;
	if (!keymaster) return false;
	return DecryptWithKeymasterKey(keymaster, km_key, extra_params, encrypted_message, key);
	}

	static bool DeleteKey(const std::string &dir) {
	std::string km_key;
	if (!android::base::ReadFileToString(dir + "/" + kFn_keymaster_key_blob, &km_key)) {
	PLOG(ERROR) << "Unable to read keymaster_key_blob from " << dir;
	return false;
	}
	Keymaster keymaster;
	if (!keymaster) return false;
	if (!keymaster.DeleteKey(km_key)) 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