src/privet/security_manager.cc - weave/libweave - Git at Google

 // Copyright 2015 The Weave Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.

 #include "src/privet/security_manager.h"

 #include <algorithm>
 #include <limits>
 #include <memory>
 #include <set>

 #include <base/bind.h>
 #include <base/guid.h>
 #include <base/logging.h>
 #include <base/rand_util.h>
 #include <base/strings/string_number_conversions.h>
 #include <base/strings/stringprintf.h>
 #include <base/time/time.h>
 #include <weave/provider/task_runner.h>

 #include "src/data_encoding.h"
 #include "src/privet/auth_manager.h"
 #include "src/privet/constants.h"
 #include "src/privet/openssl_utils.h"
 #include "src/string_utils.h"
 #include "third_party/chromium/crypto/p224_spake.h"

 namespace weave {
 namespace privet {

 namespace {

 const int kSessionExpirationTimeMinutes = 5;
 const int kPairingExpirationTimeMinutes = 5;
 const int kMaxAllowedPairingAttemts = 3;
 const int kPairingBlockingTimeMinutes = 1;

 const int kAccessTokenExpirationSeconds = 3600;

 class Spakep224Exchanger : public SecurityManager::KeyExchanger {
  public:
   explicit Spakep224Exchanger(const std::string& password)
       : spake_(crypto::P224EncryptedKeyExchange::kPeerTypeServer, password) {}
   ~Spakep224Exchanger() override = default;

   // SecurityManager::KeyExchanger methods.
   const std::string& GetMessage() override { return spake_.GetNextMessage(); }

   bool ProcessMessage(const std::string& message, ErrorPtr* error) override {
     switch (spake_.ProcessMessage(message)) {
       case crypto::P224EncryptedKeyExchange::kResultPending:
         return true;
       case crypto::P224EncryptedKeyExchange::kResultFailed:
         return Error::AddTo(error, FROM_HERE, errors::kInvalidClientCommitment,
                             spake_.error());
       default:
         LOG(FATAL) << "SecurityManager uses only one round trip";
     }
     return false;
   }

   const std::string& GetKey() const override {
     return spake_.GetUnverifiedKey();
   }

  private:
   crypto::P224EncryptedKeyExchange spake_;
 };

 }  // namespace

 SecurityManager::SecurityManager(const Config* config,
                                  AuthManager* auth_manager,
                                  provider::TaskRunner* task_runner)
     : config_{config}, auth_manager_{auth_manager}, task_runner_{task_runner} {
   CHECK(auth_manager_);
   CHECK_EQ(GetSettings().embedded_code.empty(),
            std::find(GetSettings().pairing_modes.begin(),
                      GetSettings().pairing_modes.end(),
                      PairingType::kEmbeddedCode) ==
                GetSettings().pairing_modes.end());
 }

 SecurityManager::~SecurityManager() {
   while (!pending_sessions_.empty())
     ClosePendingSession(pending_sessions_.begin()->first);
 }

 bool SecurityManager::CreateAccessTokenImpl(AuthType auth_type,
                                             AuthScope desired_scope,
                                             std::vector<uint8_t>* access_token,
                                             AuthScope* access_token_scope,
                                             base::TimeDelta* access_token_ttl) {
   auto user_id = std::to_string(++last_user_id_);
   UserInfo user_info{
       desired_scope,
       UserAppId{auth_type, {user_id.begin(), user_id.end()}, {}}};

   const base::TimeDelta kTtl =
       base::TimeDelta::FromSeconds(kAccessTokenExpirationSeconds);

   if (access_token)
     *access_token = auth_manager_->CreateAccessToken(user_info, kTtl);

   if (access_token_scope)
     *access_token_scope = user_info.scope();

   if (access_token_ttl)
     *access_token_ttl = kTtl;

   return true;
 }

 bool SecurityManager::CreateAccessTokenImpl(
     AuthType auth_type,
     const std::vector<uint8_t>& auth_code,
     AuthScope desired_scope,
     std::vector<uint8_t>* access_token,
     AuthScope* access_token_scope,
     base::TimeDelta* access_token_ttl,
     ErrorPtr* error) {
   auto disabled_mode = [](ErrorPtr* error) {
     return Error::AddTo(error, FROM_HERE, errors::kInvalidAuthMode,
                         "Mode is not available");
   };

   switch (auth_type) {
     case AuthType::kAnonymous:
       if (!IsAnonymousAuthSupported())
         return disabled_mode(error);
       return CreateAccessTokenImpl(auth_type, desired_scope, access_token,
                                    access_token_scope, access_token_ttl);
     case AuthType::kPairing:
       if (!IsPairingAuthSupported())
         return disabled_mode(error);
       if (!IsValidPairingCode(auth_code)) {
         return Error::AddTo(error, FROM_HERE, errors::kInvalidAuthCode,
                             "Invalid authCode");
       }
       return CreateAccessTokenImpl(auth_type, desired_scope, access_token,
                                    access_token_scope, access_token_ttl);
     case AuthType::kLocal:
       if (!IsLocalAuthSupported())
         return disabled_mode(error);
       const base::TimeDelta kTtl =
           base::TimeDelta::FromSeconds(kAccessTokenExpirationSeconds);
       return auth_manager_->CreateAccessTokenFromAuth(
           auth_code, kTtl, access_token, access_token_scope, access_token_ttl,
           error);
   }

   return Error::AddTo(error, FROM_HERE, errors::kInvalidAuthMode,
                       "Unsupported auth mode");
 }

 bool SecurityManager::CreateAccessToken(AuthType auth_type,
                                         const std::string& auth_code,
                                         AuthScope desired_scope,
                                         std::string* access_token,
                                         AuthScope* access_token_scope,
                                         base::TimeDelta* access_token_ttl,
                                         ErrorPtr* error) {
   std::vector<uint8_t> auth_decoded;
   if (auth_type != AuthType::kAnonymous &&
       !Base64Decode(auth_code, &auth_decoded)) {
     Error::AddToPrintf(error, FROM_HERE, errors::kInvalidAuthorization,
                        "Invalid auth_code encoding: %s", auth_code.c_str());
     return false;
   }

   std::vector<uint8_t> access_token_decoded;
   if (!CreateAccessTokenImpl(auth_type, auth_decoded, desired_scope,
                              &access_token_decoded, access_token_scope,
                              access_token_ttl, error)) {
     return false;
   }

   if (access_token)
     *access_token = Base64Encode(access_token_decoded);

   return true;
 }

 bool SecurityManager::ParseAccessToken(const std::string& token,
                                        UserInfo* user_info,
                                        ErrorPtr* error) const {
   std::vector<uint8_t> decoded;
   if (!Base64Decode(token, &decoded)) {
     Error::AddToPrintf(error, FROM_HERE, errors::kInvalidAuthorization,
                        "Invalid token encoding: %s", token.c_str());
     return false;
   }

   return auth_manager_->ParseAccessToken(decoded, user_info, error);
 }

 std::set<PairingType> SecurityManager::GetPairingTypes() const {
   return GetSettings().pairing_modes;
 }

 std::set<CryptoType> SecurityManager::GetCryptoTypes() const {
   std::set<CryptoType> result{CryptoType::kSpake_p224};
   return result;
 }

 std::set<AuthType> SecurityManager::GetAuthTypes() const {
   std::set<AuthType> result;
   if (IsAnonymousAuthSupported())
     result.insert(AuthType::kAnonymous);

   if (IsPairingAuthSupported())
     result.insert(AuthType::kPairing);

   if (IsLocalAuthSupported())
     result.insert(AuthType::kLocal);

   return result;
 }

 std::string SecurityManager::ClaimRootClientAuthToken(ErrorPtr* error) {
   return Base64Encode(auth_manager_->ClaimRootClientAuthToken(
       RootClientTokenOwner::kClient, error));
 }

 bool SecurityManager::ConfirmClientAuthToken(const std::string& token,
                                              ErrorPtr* error) {
   std::vector<uint8_t> token_decoded;
   if (!Base64Decode(token, &token_decoded)) {
     Error::AddToPrintf(error, FROM_HERE, errors::kInvalidFormat,
                        "Invalid auth token string: '%s'", token.c_str());
     return false;
   }
   return auth_manager_->ConfirmClientAuthToken(token_decoded, error);
 }

 const Config::Settings& SecurityManager::GetSettings() const {
   return config_->GetSettings();
 }

 bool SecurityManager::IsValidPairingCode(
     const std::vector<uint8_t>& auth_code) const {
   for (const auto& session : confirmed_sessions_) {
     const std::string& key = session.second->GetKey();
     const std::string& id = session.first;
     if (auth_code == HmacSha256(std::vector<uint8_t>(key.begin(), key.end()),
                                 std::vector<uint8_t>(id.begin(), id.end()))) {
       pairing_attemts_ = 0;
       block_pairing_until_ = base::Time{};
       return true;
     }
   }
   LOG(ERROR) << "Attempt to authenticate with invalide code.";
   return false;
 }

 bool SecurityManager::StartPairing(PairingType mode,
                                    CryptoType crypto,
                                    std::string* session_id,
                                    std::string* device_commitment,
                                    ErrorPtr* error) {
   if (!CheckIfPairingAllowed(error))
     return false;

   const auto& pairing_modes = GetSettings().pairing_modes;
   if (std::find(pairing_modes.begin(), pairing_modes.end(), mode) ==
       pairing_modes.end()) {
     return Error::AddTo(error, FROM_HERE, errors::kInvalidParams,
                         "Pairing mode is not enabled");
   }

   std::string code;
   switch (mode) {
     case PairingType::kEmbeddedCode:
       CHECK(!GetSettings().embedded_code.empty());
       code = GetSettings().embedded_code;
       break;
     case PairingType::kPinCode:
       code = base::StringPrintf("%04i", base::RandInt(0, 9999));
       break;
     default:
       return Error::AddTo(error, FROM_HERE, errors::kInvalidParams,
                           "Unsupported pairing mode");
   }

   std::unique_ptr<KeyExchanger> spake;
   switch (crypto) {
     case CryptoType::kSpake_p224:
       spake.reset(new Spakep224Exchanger(code));
       break;
     // Fall through...
     default:
       return Error::AddTo(error, FROM_HERE, errors::kInvalidParams,
                           "Unsupported crypto");
   }

   // Allow only a single session at a time for now.
   while (!pending_sessions_.empty())
     ClosePendingSession(pending_sessions_.begin()->first);

   std::string session;
   do {
     session = base::GenerateGUID();
   } while (confirmed_sessions_.find(session) != confirmed_sessions_.end() ||
            pending_sessions_.find(session) != pending_sessions_.end());
   std::string commitment = spake->GetMessage();
   pending_sessions_.insert(std::make_pair(session, std::move(spake)));

   task_runner_->PostDelayedTask(
       FROM_HERE,
       base::Bind(base::IgnoreResult(&SecurityManager::ClosePendingSession),
                  weak_ptr_factory_.GetWeakPtr(), session),
       base::TimeDelta::FromMinutes(kPairingExpirationTimeMinutes));

   *session_id = session;
   *device_commitment = Base64Encode(commitment);
   LOG(INFO) << "Pairing code for session " << *session_id << " is " << code;
   // TODO(vitalybuka): Handle case when device can't start multiple pairing
   // simultaneously and implement throttling to avoid brute force attack.
   if (!on_start_.is_null()) {
     on_start_.Run(session, mode,
                   std::vector<uint8_t>{code.begin(), code.end()});
   }

   return true;
 }

 bool SecurityManager::ConfirmPairing(const std::string& session_id,
                                      const std::string& client_commitment,
                                      std::string* fingerprint,
                                      std::string* signature,
                                      ErrorPtr* error) {
   auto session = pending_sessions_.find(session_id);
   if (session == pending_sessions_.end()) {
     Error::AddToPrintf(error, FROM_HERE, errors::kUnknownSession,
                        "Unknown session id: '%s'", session_id.c_str());
     return false;
   }

   std::vector<uint8_t> commitment;
   if (!Base64Decode(client_commitment, &commitment)) {
     ClosePendingSession(session_id);
     Error::AddToPrintf(error, FROM_HERE, errors::kInvalidFormat,
                        "Invalid commitment string: '%s'",
                        client_commitment.c_str());
     return false;
   }

   if (!session->second->ProcessMessage(
           std::string(commitment.begin(), commitment.end()), error)) {
     ClosePendingSession(session_id);
     return Error::AddTo(error, FROM_HERE, errors::kCommitmentMismatch,
                         "Pairing code or crypto implementation mismatch");
   }

   const std::string& key = session->second->GetKey();
   VLOG(3) << "KEY " << base::HexEncode(key.data(), key.size());

   const auto& certificate_fingerprint =
       auth_manager_->GetCertificateFingerprint();
   *fingerprint = Base64Encode(certificate_fingerprint);
   std::vector<uint8_t> cert_hmac = HmacSha256(
       std::vector<uint8_t>(key.begin(), key.end()), certificate_fingerprint);
   *signature = Base64Encode(cert_hmac);
   confirmed_sessions_.insert(
       std::make_pair(session->first, std::move(session->second)));
   task_runner_->PostDelayedTask(
       FROM_HERE,
       base::Bind(base::IgnoreResult(&SecurityManager::CloseConfirmedSession),
                  weak_ptr_factory_.GetWeakPtr(), session_id),
       base::TimeDelta::FromMinutes(kSessionExpirationTimeMinutes));
   ClosePendingSession(session_id);
   return true;
 }

 bool SecurityManager::CancelPairing(const std::string& session_id,
                                     ErrorPtr* error) {
   bool confirmed = CloseConfirmedSession(session_id);
   bool pending = ClosePendingSession(session_id);
   if (pending) {
     CHECK_GE(pairing_attemts_, 1);
     --pairing_attemts_;
   }
   CHECK(!confirmed || !pending);
   if (confirmed || pending)
     return true;
   Error::AddToPrintf(error, FROM_HERE, errors::kUnknownSession,
                      "Unknown session id: '%s'", session_id.c_str());
   return false;
 }

 std::string SecurityManager::CreateSessionId() {
   return auth_manager_->CreateSessionId();
 }

 void SecurityManager::RegisterPairingListeners(
     const PairingStartListener& on_start,
     const PairingEndListener& on_end) {
   CHECK(on_start_.is_null() && on_end_.is_null());
   on_start_ = on_start;
   on_end_ = on_end;
 }

 bool SecurityManager::CheckIfPairingAllowed(ErrorPtr* error) {
   if (block_pairing_until_ > auth_manager_->Now()) {
     return Error::AddTo(error, FROM_HERE, errors::kDeviceBusy,
                         "Too many pairing attempts");
   }

   if (++pairing_attemts_ >= kMaxAllowedPairingAttemts) {
     LOG(INFO) << "Pairing blocked for" << kPairingBlockingTimeMinutes
               << "minutes.";
     block_pairing_until_ = auth_manager_->Now();
     block_pairing_until_ +=
         base::TimeDelta::FromMinutes(kPairingBlockingTimeMinutes);
   }

   return true;
 }

 bool SecurityManager::ClosePendingSession(const std::string& session_id) {
   // The most common source of these session_id values is the map containing
   // the sessions, which we're about to clear out.  Make a local copy.
   const std::string safe_session_id{session_id};
   const size_t num_erased = pending_sessions_.erase(safe_session_id);
   if (num_erased > 0 && !on_end_.is_null())
     on_end_.Run(safe_session_id);
   return num_erased != 0;
 }

 bool SecurityManager::CloseConfirmedSession(const std::string& session_id) {
   return confirmed_sessions_.erase(session_id) != 0;
 }

 bool SecurityManager::IsAnonymousAuthSupported() const {
   return GetSettings().local_anonymous_access_role != AuthScope::kNone;
 }

 bool SecurityManager::IsPairingAuthSupported() const {
   return GetSettings().local_pairing_enabled;
 }

 bool SecurityManager::IsLocalAuthSupported() const {
   return GetSettings().root_client_token_owner != RootClientTokenOwner::kNone;
 }

 }  // namespace privet
 }  // namespace weave
	// Copyright 2015 The Weave Authors. All rights reserved.
	// Use of this source code is governed by a BSD-style license that can be
	// found in the LICENSE file.

	#include "src/privet/security_manager.h"

	#include <algorithm>
	#include <limits>
	#include <memory>
	#include <set>

	#include <base/bind.h>
	#include <base/guid.h>
	#include <base/logging.h>
	#include <base/rand_util.h>
	#include <base/strings/string_number_conversions.h>
	#include <base/strings/stringprintf.h>
	#include <base/time/time.h>
	#include <weave/provider/task_runner.h>

	#include "src/data_encoding.h"
	#include "src/privet/auth_manager.h"
	#include "src/privet/constants.h"
	#include "src/privet/openssl_utils.h"
	#include "src/string_utils.h"
	#include "third_party/chromium/crypto/p224_spake.h"

	namespace weave {
	namespace privet {

	namespace {

	const int kSessionExpirationTimeMinutes = 5;
	const int kPairingExpirationTimeMinutes = 5;
	const int kMaxAllowedPairingAttemts = 3;
	const int kPairingBlockingTimeMinutes = 1;

	const int kAccessTokenExpirationSeconds = 3600;

	class Spakep224Exchanger : public SecurityManager::KeyExchanger {
	public:
	explicit Spakep224Exchanger(const std::string& password)
	: spake_(crypto::P224EncryptedKeyExchange::kPeerTypeServer, password) {}
	~Spakep224Exchanger() override = default;

	// SecurityManager::KeyExchanger methods.
	const std::string& GetMessage() override { return spake_.GetNextMessage(); }

	bool ProcessMessage(const std::string& message, ErrorPtr* error) override {
	switch (spake_.ProcessMessage(message)) {
	case crypto::P224EncryptedKeyExchange::kResultPending:
	return true;
	case crypto::P224EncryptedKeyExchange::kResultFailed:
	return Error::AddTo(error, FROM_HERE, errors::kInvalidClientCommitment,
	spake_.error());
	default:
	LOG(FATAL) << "SecurityManager uses only one round trip";
	}
	return false;
	}

	const std::string& GetKey() const override {
	return spake_.GetUnverifiedKey();
	}

	private:
	crypto::P224EncryptedKeyExchange spake_;
	};

	} // namespace

	SecurityManager::SecurityManager(const Config* config,
	AuthManager* auth_manager,
	provider::TaskRunner* task_runner)
	: config_{config}, auth_manager_{auth_manager}, task_runner_{task_runner} {
	CHECK(auth_manager_);
	CHECK_EQ(GetSettings().embedded_code.empty(),
	std::find(GetSettings().pairing_modes.begin(),
	GetSettings().pairing_modes.end(),
	PairingType::kEmbeddedCode) ==
	GetSettings().pairing_modes.end());
	}

	SecurityManager::~SecurityManager() {
	while (!pending_sessions_.empty())
	ClosePendingSession(pending_sessions_.begin()->first);
	}

	bool SecurityManager::CreateAccessTokenImpl(AuthType auth_type,
	AuthScope desired_scope,
	std::vector<uint8_t>* access_token,
	AuthScope* access_token_scope,
	base::TimeDelta* access_token_ttl) {
	auto user_id = std::to_string(++last_user_id_);
	UserInfo user_info{
	desired_scope,
	UserAppId{auth_type, {user_id.begin(), user_id.end()}, {}}};

	const base::TimeDelta kTtl =
	base::TimeDelta::FromSeconds(kAccessTokenExpirationSeconds);

	if (access_token)
	*access_token = auth_manager_->CreateAccessToken(user_info, kTtl);

	if (access_token_scope)
	*access_token_scope = user_info.scope();

	if (access_token_ttl)
	*access_token_ttl = kTtl;

	return true;
	}

	bool SecurityManager::CreateAccessTokenImpl(
	AuthType auth_type,
	const std::vector<uint8_t>& auth_code,
	AuthScope desired_scope,
	std::vector<uint8_t>* access_token,
	AuthScope* access_token_scope,
	base::TimeDelta* access_token_ttl,
	ErrorPtr* error) {
	auto disabled_mode = [](ErrorPtr* error) {
	return Error::AddTo(error, FROM_HERE, errors::kInvalidAuthMode,
	"Mode is not available");
	};

	switch (auth_type) {
	case AuthType::kAnonymous:
	if (!IsAnonymousAuthSupported())
	return disabled_mode(error);
	return CreateAccessTokenImpl(auth_type, desired_scope, access_token,
	access_token_scope, access_token_ttl);
	case AuthType::kPairing:
	if (!IsPairingAuthSupported())
	return disabled_mode(error);
	if (!IsValidPairingCode(auth_code)) {
	return Error::AddTo(error, FROM_HERE, errors::kInvalidAuthCode,
	"Invalid authCode");
	}
	return CreateAccessTokenImpl(auth_type, desired_scope, access_token,
	access_token_scope, access_token_ttl);
	case AuthType::kLocal:
	if (!IsLocalAuthSupported())
	return disabled_mode(error);
	const base::TimeDelta kTtl =
	base::TimeDelta::FromSeconds(kAccessTokenExpirationSeconds);
	return auth_manager_->CreateAccessTokenFromAuth(
	auth_code, kTtl, access_token, access_token_scope, access_token_ttl,
	error);
	}

	return Error::AddTo(error, FROM_HERE, errors::kInvalidAuthMode,
	"Unsupported auth mode");
	}

	bool SecurityManager::CreateAccessToken(AuthType auth_type,
	const std::string& auth_code,
	AuthScope desired_scope,
	std::string* access_token,
	AuthScope* access_token_scope,
	base::TimeDelta* access_token_ttl,
	ErrorPtr* error) {
	std::vector<uint8_t> auth_decoded;
	if (auth_type != AuthType::kAnonymous &&
	!Base64Decode(auth_code, &auth_decoded)) {
	Error::AddToPrintf(error, FROM_HERE, errors::kInvalidAuthorization,
	"Invalid auth_code encoding: %s", auth_code.c_str());
	return false;
	}

	std::vector<uint8_t> access_token_decoded;
	if (!CreateAccessTokenImpl(auth_type, auth_decoded, desired_scope,
	&access_token_decoded, access_token_scope,
	access_token_ttl, error)) {
	return false;
	}

	if (access_token)
	*access_token = Base64Encode(access_token_decoded);

	return true;
	}

	bool SecurityManager::ParseAccessToken(const std::string& token,
	UserInfo* user_info,
	ErrorPtr* error) const {
	std::vector<uint8_t> decoded;
	if (!Base64Decode(token, &decoded)) {
	Error::AddToPrintf(error, FROM_HERE, errors::kInvalidAuthorization,
	"Invalid token encoding: %s", token.c_str());
	return false;
	}

	return auth_manager_->ParseAccessToken(decoded, user_info, error);
	}

	std::set<PairingType> SecurityManager::GetPairingTypes() const {
	return GetSettings().pairing_modes;
	}

	std::set<CryptoType> SecurityManager::GetCryptoTypes() const {
	std::set<CryptoType> result{CryptoType::kSpake_p224};
	return result;
	}

	std::set<AuthType> SecurityManager::GetAuthTypes() const {
	std::set<AuthType> result;
	if (IsAnonymousAuthSupported())
	result.insert(AuthType::kAnonymous);

	if (IsPairingAuthSupported())
	result.insert(AuthType::kPairing);

	if (IsLocalAuthSupported())
	result.insert(AuthType::kLocal);

	return result;
	}

	std::string SecurityManager::ClaimRootClientAuthToken(ErrorPtr* error) {
	return Base64Encode(auth_manager_->ClaimRootClientAuthToken(
	RootClientTokenOwner::kClient, error));
	}

	bool SecurityManager::ConfirmClientAuthToken(const std::string& token,
	ErrorPtr* error) {
	std::vector<uint8_t> token_decoded;
	if (!Base64Decode(token, &token_decoded)) {
	Error::AddToPrintf(error, FROM_HERE, errors::kInvalidFormat,
	"Invalid auth token string: '%s'", token.c_str());
	return false;
	}
	return auth_manager_->ConfirmClientAuthToken(token_decoded, error);
	}

	const Config::Settings& SecurityManager::GetSettings() const {
	return config_->GetSettings();
	}

	bool SecurityManager::IsValidPairingCode(
	const std::vector<uint8_t>& auth_code) const {
	for (const auto& session : confirmed_sessions_) {
	const std::string& key = session.second->GetKey();
	const std::string& id = session.first;
	if (auth_code == HmacSha256(std::vector<uint8_t>(key.begin(), key.end()),
	std::vector<uint8_t>(id.begin(), id.end()))) {
	pairing_attemts_ = 0;
	block_pairing_until_ = base::Time{};
	return true;
	}
	}
	LOG(ERROR) << "Attempt to authenticate with invalide code.";
	return false;
	}

	bool SecurityManager::StartPairing(PairingType mode,
	CryptoType crypto,
	std::string* session_id,
	std::string* device_commitment,
	ErrorPtr* error) {
	if (!CheckIfPairingAllowed(error))
	return false;

	const auto& pairing_modes = GetSettings().pairing_modes;
	if (std::find(pairing_modes.begin(), pairing_modes.end(), mode) ==
	pairing_modes.end()) {
	return Error::AddTo(error, FROM_HERE, errors::kInvalidParams,
	"Pairing mode is not enabled");
	}

	std::string code;
	switch (mode) {
	case PairingType::kEmbeddedCode:
	CHECK(!GetSettings().embedded_code.empty());
	code = GetSettings().embedded_code;
	break;
	case PairingType::kPinCode:
	code = base::StringPrintf("%04i", base::RandInt(0, 9999));
	break;
	default:
	return Error::AddTo(error, FROM_HERE, errors::kInvalidParams,
	"Unsupported pairing mode");
	}

	std::unique_ptr<KeyExchanger> spake;
	switch (crypto) {
	case CryptoType::kSpake_p224:
	spake.reset(new Spakep224Exchanger(code));
	break;
	// Fall through...
	default:
	return Error::AddTo(error, FROM_HERE, errors::kInvalidParams,
	"Unsupported crypto");
	}

	// Allow only a single session at a time for now.
	while (!pending_sessions_.empty())
	ClosePendingSession(pending_sessions_.begin()->first);

	std::string session;
	do {
	session = base::GenerateGUID();
	} while (confirmed_sessions_.find(session) != confirmed_sessions_.end() \|\|
	pending_sessions_.find(session) != pending_sessions_.end());
	std::string commitment = spake->GetMessage();
	pending_sessions_.insert(std::make_pair(session, std::move(spake)));

	task_runner_->PostDelayedTask(
	FROM_HERE,
	base::Bind(base::IgnoreResult(&SecurityManager::ClosePendingSession),
	weak_ptr_factory_.GetWeakPtr(), session),
	base::TimeDelta::FromMinutes(kPairingExpirationTimeMinutes));

	*session_id = session;
	*device_commitment = Base64Encode(commitment);
	LOG(INFO) << "Pairing code for session " << *session_id << " is " << code;
	// TODO(vitalybuka): Handle case when device can't start multiple pairing
	// simultaneously and implement throttling to avoid brute force attack.
	if (!on_start_.is_null()) {
	on_start_.Run(session, mode,
	std::vector<uint8_t>{code.begin(), code.end()});
	}

	return true;
	}

	bool SecurityManager::ConfirmPairing(const std::string& session_id,
	const std::string& client_commitment,
	std::string* fingerprint,
	std::string* signature,
	ErrorPtr* error) {
	auto session = pending_sessions_.find(session_id);
	if (session == pending_sessions_.end()) {
	Error::AddToPrintf(error, FROM_HERE, errors::kUnknownSession,
	"Unknown session id: '%s'", session_id.c_str());
	return false;
	}

	std::vector<uint8_t> commitment;
	if (!Base64Decode(client_commitment, &commitment)) {
	ClosePendingSession(session_id);
	Error::AddToPrintf(error, FROM_HERE, errors::kInvalidFormat,
	"Invalid commitment string: '%s'",
	client_commitment.c_str());
	return false;
	}

	if (!session->second->ProcessMessage(
	std::string(commitment.begin(), commitment.end()), error)) {
	ClosePendingSession(session_id);
	return Error::AddTo(error, FROM_HERE, errors::kCommitmentMismatch,
	"Pairing code or crypto implementation mismatch");
	}

	const std::string& key = session->second->GetKey();
	VLOG(3) << "KEY " << base::HexEncode(key.data(), key.size());

	const auto& certificate_fingerprint =
	auth_manager_->GetCertificateFingerprint();
	*fingerprint = Base64Encode(certificate_fingerprint);
	std::vector<uint8_t> cert_hmac = HmacSha256(
	std::vector<uint8_t>(key.begin(), key.end()), certificate_fingerprint);
	*signature = Base64Encode(cert_hmac);
	confirmed_sessions_.insert(
	std::make_pair(session->first, std::move(session->second)));
	task_runner_->PostDelayedTask(
	FROM_HERE,
	base::Bind(base::IgnoreResult(&SecurityManager::CloseConfirmedSession),
	weak_ptr_factory_.GetWeakPtr(), session_id),
	base::TimeDelta::FromMinutes(kSessionExpirationTimeMinutes));
	ClosePendingSession(session_id);
	return true;
	}

	bool SecurityManager::CancelPairing(const std::string& session_id,
	ErrorPtr* error) {
	bool confirmed = CloseConfirmedSession(session_id);
	bool pending = ClosePendingSession(session_id);
	if (pending) {
	CHECK_GE(pairing_attemts_, 1);
	--pairing_attemts_;
	}
	CHECK(!confirmed \|\| !pending);
	if (confirmed \|\| pending)
	return true;
	Error::AddToPrintf(error, FROM_HERE, errors::kUnknownSession,
	"Unknown session id: '%s'", session_id.c_str());
	return false;
	}

	std::string SecurityManager::CreateSessionId() {
	return auth_manager_->CreateSessionId();
	}

	void SecurityManager::RegisterPairingListeners(
	const PairingStartListener& on_start,
	const PairingEndListener& on_end) {
	CHECK(on_start_.is_null() && on_end_.is_null());
	on_start_ = on_start;
	on_end_ = on_end;
	}

	bool SecurityManager::CheckIfPairingAllowed(ErrorPtr* error) {
	if (block_pairing_until_ > auth_manager_->Now()) {
	return Error::AddTo(error, FROM_HERE, errors::kDeviceBusy,
	"Too many pairing attempts");
	}

	if (++pairing_attemts_ >= kMaxAllowedPairingAttemts) {
	LOG(INFO) << "Pairing blocked for" << kPairingBlockingTimeMinutes
	<< "minutes.";
	block_pairing_until_ = auth_manager_->Now();
	block_pairing_until_ +=
	base::TimeDelta::FromMinutes(kPairingBlockingTimeMinutes);
	}

	return true;
	}

	bool SecurityManager::ClosePendingSession(const std::string& session_id) {
	// The most common source of these session_id values is the map containing
	// the sessions, which we're about to clear out. Make a local copy.
	const std::string safe_session_id{session_id};
	const size_t num_erased = pending_sessions_.erase(safe_session_id);
	if (num_erased > 0 && !on_end_.is_null())
	on_end_.Run(safe_session_id);
	return num_erased != 0;
	}

	bool SecurityManager::CloseConfirmedSession(const std::string& session_id) {
	return confirmed_sessions_.erase(session_id) != 0;
	}

	bool SecurityManager::IsAnonymousAuthSupported() const {
	return GetSettings().local_anonymous_access_role != AuthScope::kNone;
	}

	bool SecurityManager::IsPairingAuthSupported() const {
	return GetSettings().local_pairing_enabled;
	}

	bool SecurityManager::IsLocalAuthSupported() const {
	return GetSettings().root_client_token_owner != RootClientTokenOwner::kNone;
	}

	} // namespace privet
	} // namespace weave