Implement authenticator based on SPAKE2 implementation in boringssl.

remoting/protocol/spake2_authenticator.cc

Index: remoting/protocol/spake2_authenticator.cc
diff --git a/remoting/protocol/spake2_authenticator.cc b/remoting/protocol/spake2_authenticator.cc
new file mode 100644
index 0000000000000000000000000000000000000000..d7c0a6c5550b945cf71a539da116b805862bd12d
--- /dev/null
+++ b/remoting/protocol/spake2_authenticator.cc
@@ -0,0 +1,317 @@
+// Copyright 2016 The Chromium 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 "remoting/protocol/spake2_authenticator.h"
+
+#include <utility>
+
+#include "base/base64.h"
+#include "base/logging.h"
+#include "base/sys_byteorder.h"
+#include "crypto/hmac.h"
+#include "crypto/secure_util.h"
+#include "remoting/base/constants.h"
+#include "remoting/base/rsa_key_pair.h"
+#include "remoting/protocol/ssl_hmac_channel_authenticator.h"
+#include "third_party/boringssl/src/include/openssl/curve25519.h"
+#include "third_party/webrtc/libjingle/xmllite/xmlelement.h"
+
+namespace remoting {
+namespace protocol {
+
+namespace {
+
+// Each peer sends 2 messages: <spake-message> and <verification-hash>. The
+// content of <spake-message> is the output of SPAKE2_generate_msg() and must
+// be passed to SPAKE2_process_msg() on the other end. This is enough to
+// generate authentication key. <verification-hash> is sent to confirm that both
+// ends get the same authentication key (which means they both know the
+// password). This verification hash is calculated in
+// CalculateVerificationHash() as follows:
+//    HMAC_SHA256(auth_key, ("host"|"client") + local_jid.length() + local_jid +
+//                remote_jid.length() + remote_jid)
+// where auth_key is the key produced by SPAKE2.
+
+const buzz::StaticQName kSpakeMessageTag = {kChromotingXmlNamespace,
+                                            "spake-message"};
+const buzz::StaticQName kVerificationHashTag = {kChromotingXmlNamespace,
+                                                "verification-hash"};
+const buzz::StaticQName kCertificateTag = {kChromotingXmlNamespace,
+                                           "certificate"};
+
+scoped_ptr<buzz::XmlElement> EncodeBinaryValueToXml(
+    const buzz::StaticQName& qname,
+    const std::string& content) {
+  std::string content_base64;
+  base::Base64Encode(content, &content_base64);
+
+  scoped_ptr<buzz::XmlElement> result(new buzz::XmlElement(qname));
+  result->SetBodyText(content_base64);
+  return result;
+}
+
+// Finds tag named |qname| in base_message and decodes it from base64 and stores
+// in |data|. If the element is not present then found is set to false otherwise
+// it's set to true. If the element is there and it's content cound't be decoded
+// then false is returned.
+bool DecodeBinaryValueFromXml(const buzz::XmlElement* message,
+                              const buzz::QName& qname,
+                              bool* found,
+                              std::string* data) {
+  const buzz::XmlElement* element = message->FirstNamed(qname);
+  *found = element != nullptr;
+  if (!*found)
+    return true;
+
+  if (!base::Base64Decode(element->BodyText(), data)) {
+    LOG(WARNING) << "Failed to parse " << qname.LocalPart();
+    return false;
+  }
+
+  return !data->empty();
+}
+
+std::string PrefixWithLength(const std::string& str) {
+  uint32_t length = base::HostToNet32(str.size());
+  return std::string(reinterpret_cast<char*>(&length), sizeof(length)) + str;
+}
+
+}  // namespace
+
+// static
+scoped_ptr<Authenticator> Spake2Authenticator::CreateForClient(
+    const std::string& local_id,
+    const std::string& remote_id,
+    const std::string& shared_secret,
+    Authenticator::State initial_state) {
+  return make_scoped_ptr(new Spake2Authenticator(
+      local_id, remote_id, shared_secret, false, initial_state));
+}
+
+// static
+scoped_ptr<Authenticator> Spake2Authenticator::CreateForHost(
+    const std::string& local_id,
+    const std::string& remote_id,
+    const std::string& shared_secret,
+    const std::string& local_cert,
+    scoped_refptr<RsaKeyPair> key_pair,
+    Authenticator::State initial_state) {
+  scoped_ptr<Spake2Authenticator> result(new Spake2Authenticator(
+      local_id, remote_id, shared_secret, true, initial_state));
+  result->local_cert_ = local_cert;
+  result->local_key_pair_ = key_pair;
+  return std::move(result);
+}
+
+Spake2Authenticator::Spake2Authenticator(const std::string& local_id,
+                                         const std::string& remote_id,
+                                         const std::string& shared_secret,
+                                         bool is_host,
+                                         Authenticator::State initial_state)
+    : local_id_(local_id),
+      remote_id_(remote_id),
+      shared_secret_(shared_secret),
+      is_host_(is_host),
+      state_(initial_state) {
+  spake2_context_ = SPAKE2_CTX_new(
+      is_host ? spake2_role_bob : spake2_role_alice,
+      reinterpret_cast<const uint8_t*>(local_id_.data()), local_id_.size(),
+      reinterpret_cast<const uint8_t*>(remote_id_.data()), remote_id_.size());
+
+  // Generate first message and push it to |pending_messages_|.
+  uint8_t message[SPAKE2_MAX_MSG_SIZE];
+  size_t message_size;
+  int result = SPAKE2_generate_msg(
+      spake2_context_, message, &message_size, sizeof(message),
+      reinterpret_cast<const uint8_t*>(shared_secret_.data()),
+      shared_secret_.size());
+  CHECK(result);
+  local_spake_message_.assign(reinterpret_cast<char*>(message), message_size);
+}
+
+Spake2Authenticator::~Spake2Authenticator() {
+  SPAKE2_CTX_free(spake2_context_);
+}
+
+Authenticator::State Spake2Authenticator::state() const {
+  if (state_ == ACCEPTED && !outgoing_verification_hash_.empty())
+    return MESSAGE_READY;
+  return state_;
+}
+
+bool Spake2Authenticator::started() const {
+  return started_;
+}
+
+Authenticator::RejectionReason Spake2Authenticator::rejection_reason() const {
+  DCHECK_EQ(state(), REJECTED);
+  return rejection_reason_;
+}
+
+void Spake2Authenticator::ProcessMessage(const buzz::XmlElement* message,
+                                         const base::Closure& resume_callback) {
+  ProcessMessageInternal(message);
+  resume_callback.Run();
+}
+
+void Spake2Authenticator::ProcessMessageInternal(
+    const buzz::XmlElement* message) {
+  DCHECK_EQ(state(), WAITING_MESSAGE);
+
+  // Parse the certificate.
+  bool cert_present;
+  if (!DecodeBinaryValueFromXml(message, kCertificateTag, &cert_present,
+                                &remote_cert_)) {
+    state_ = REJECTED;
+    rejection_reason_ = PROTOCOL_ERROR;
+    return;
+  }
+
+  // Client always expects certificate in the first message.
+  if (!is_host_ && remote_cert_.empty()) {
+    LOG(WARNING) << "No valid host certificate.";
+    state_ = REJECTED;
+    rejection_reason_ = PROTOCOL_ERROR;
+    return;
+  }
+
+  bool spake_message_present = false;
+  std::string spake_message;
+  bool verification_hash_present = false;
+  std::string verification_hash;
+  if (!DecodeBinaryValueFromXml(message, kSpakeMessageTag,
+                                &spake_message_present, &spake_message) ||
+      !DecodeBinaryValueFromXml(message, kVerificationHashTag,
+                                &verification_hash_present,
+                                &verification_hash)) {
+    state_ = REJECTED;
+    rejection_reason_ = PROTOCOL_ERROR;
+    return;
+  }
+
+  // |auth_key_| is generated when <spake-message> is received.
+  if (auth_key_.empty()) {
+    if (!spake_message_present) {
+      LOG(WARNING) << "<spake-message> not found.";
+      state_ = REJECTED;
+      rejection_reason_ = PROTOCOL_ERROR;
+      return;
+    }
+    uint8_t key[SPAKE2_MAX_KEY_SIZE];
+    size_t key_size;
+    started_ = true;
+    int result = SPAKE2_process_msg(
+        spake2_context_, key, &key_size, sizeof(key),
+        reinterpret_cast<const uint8_t*>(spake_message.data()),
+        spake_message.size());
+    if (!result) {
+      state_ = REJECTED;
+      rejection_reason_ = INVALID_CREDENTIALS;
+      return;
+    }
+    CHECK(key_size);
+    auth_key_.assign(reinterpret_cast<char*>(key), key_size);
+
+    outgoing_verification_hash_ =
+        CalculateVerificationHash(is_host_, local_id_, remote_id_);
+    expected_verification_hash_ =
+        CalculateVerificationHash(!is_host_, remote_id_, local_id_);
+  } else if (spake_message_present) {
+    LOG(WARNING) << "Received duplicate <spake-message>.";
+    state_ = REJECTED;
+    rejection_reason_ = PROTOCOL_ERROR;
+    return;
+  }
+
+  if (spake_message_sent_ && !verification_hash_present) {
+    LOG(WARNING) << "Didn't receive <verification-hash> when expected.";
+    state_ = REJECTED;
+    rejection_reason_ = PROTOCOL_ERROR;
+    return;
+  }
+
+  if (verification_hash_present) {
+    if (verification_hash.size() != expected_verification_hash_.size() ||
+        !crypto::SecureMemEqual(verification_hash.data(),
+                                expected_verification_hash_.data(),
+                                verification_hash.size())) {
+      state_ = REJECTED;
+      rejection_reason_ = INVALID_CREDENTIALS;
+      return;
+    }
+    state_ = ACCEPTED;
+    return;
+  }
+
+  state_ = MESSAGE_READY;
+}
+
+scoped_ptr<buzz::XmlElement> Spake2Authenticator::GetNextMessage() {
+  DCHECK_EQ(state(), MESSAGE_READY);
+
+  scoped_ptr<buzz::XmlElement> message = CreateEmptyAuthenticatorMessage();
+
+  if (!spake_message_sent_) {
+    if (!local_cert_.empty()) {
+      message->AddElement(
+          EncodeBinaryValueToXml(kCertificateTag, local_cert_).release());
+    }
+
+    message->AddElement(
+        EncodeBinaryValueToXml(kSpakeMessageTag, local_spake_message_)
+            .release());
+
+    spake_message_sent_ = true;
+  }
+
+  if (!outgoing_verification_hash_.empty()) {
+    message->AddElement(EncodeBinaryValueToXml(kVerificationHashTag,
+                                               outgoing_verification_hash_)
+                            .release());
+    outgoing_verification_hash_.clear();
+  }
+
+  if (state_ != ACCEPTED) {
+    state_ = WAITING_MESSAGE;
+  }
+  return message;
+}
+
+const std::string& Spake2Authenticator::GetAuthKey() const {
+  return auth_key_;
+}
+
+scoped_ptr<ChannelAuthenticator>
+Spake2Authenticator::CreateChannelAuthenticator() const {
+  DCHECK_EQ(state(), ACCEPTED);
+  CHECK(!auth_key_.empty());
+
+  if (is_host_) {
+    return SslHmacChannelAuthenticator::CreateForHost(
+        local_cert_, local_key_pair_, auth_key_);
+  } else {
+    return SslHmacChannelAuthenticator::CreateForClient(remote_cert_,
+                                                        auth_key_);
+  }
+}
+
+std::string Spake2Authenticator::CalculateVerificationHash(
+    bool from_host,
+    const std::string& local_id,
+    const std::string& remote_id) {
+  std::string message = (from_host ? "host" : "client") +
+                        PrefixWithLength(local_id) +
+                        PrefixWithLength(remote_id);
+  crypto::HMAC hmac(crypto::HMAC::SHA256);
+  std::string result(hmac.DigestLength(), '\0');
+  if (!hmac.Init(auth_key_) ||
+      !hmac.Sign(message, reinterpret_cast<uint8_t*>(&result[0]),
+                 result.length())) {
+    LOG(FATAL) << "Failed to calculate HMAC.";
+  }
+  return result;
+}
+
+}  // namespace protocol
+}  // namespace remoting