Certificate Transparency: Fetching of Signed Tree Heads (DRAFT)

components/certificate_transparency/tree_state_tracker.cc

+// Copyright 2015 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 "components/certificate_transparency/tree_state_tracker.h"
+
+#include "base/thread_task_runner_handle.h"
+#include "components/certificate_transparency/log_proof_fetcher.h"
+#include "content/public/browser/browser_thread.h"
+#include "net/cert/ct_log_verifier.h"
+#include "net/cert/signed_certificate_timestamp.h"
+#include "net/cert/signed_tree_head.h"
+
+namespace certificate_transparency {
+
+TreeStateTracker::TreeStateTracker(
+    scoped_ptr<LogProofFetcher> fetcher,
+    const std::vector<linked_ptr<net::CTLogVerifier>>& ct_logs)
+    : fetcher_(fetcher.Pass()) {
+  for (auto it = ct_logs.begin(); it != ct_logs.end(); ++it) {
+    linked_ptr<net::CTLogVerifier> log(*it);
+    ct_logs_[log->key_id()] = log;
+  }
+  content::BrowserThread::PostAfterStartupTask(
+      FROM_HERE, base::ThreadTaskRunnerHandle::Get(),
+      base::Bind(&TreeStateTracker::RefreshSTHs, base::Unretained(this)));
+}
+
+TreeStateTracker::~TreeStateTracker() {
+}
+
+void TreeStateTracker::OnSCTVerified(
+    const net::ct::SignedCertificateTimestamp* sct,
+    net::CTLogVerifier* verifier) {
+  VLOG(0) << "Verified SCT observed.";
+  // 1st step: Check if an sth for the log with this ID exists. If not, fetch.
+  // 2nd step: Check if timestamp in sct > timestamp in sth. If yes, fetch
+  // fresher STH.
+}
+
+void TreeStateTracker::RefreshSTHs() {
+  // TODO(eranm): Verify that base::Unretained usage here is fine since
+  // this class owns the fetcher and the fetcher, when deleted, will delete
+  // all pending requests, so this class always outlives the fetcher.
+  LogProofFetcher::FetchSTHCallback cb =
+      base::Bind(&TreeStateTracker::OnSTHFetched, base::Unretained(this));
+  for (auto it = ct_logs_.begin(); it != ct_logs_.end(); ++it) {
+    VLOG(0) << "Fetching STH for log " << it->second.get()->description();
+    net::CTLogVerifier* log(it->second.get());
+    fetcher_->FetchSTH(log->url(), log->key_id(), cb);
+  }
+}
+
+void TreeStateTracker::OnSTHFetched(
+    const std::string& log_id,
+    const net::ct::SignedTreeHead& unverified_sth) {
+  VLOG(0) << "Received unverified sth.";
+  auto it = ct_logs_.find(log_id);
+  if (it == ct_logs_.end()) {
+    VLOG(0) << "STH is for unknown log!.";
+    return;
+  }
+
+  net::CTLogVerifier* log(it->second.get());
+  if (!log->VerifySignedTreeHead(unverified_sth)) {
+    VLOG(0) << "STH is for " << log->url() << " could not be verified.";
+    return;
+  }
+  VLOG(0) << "Signature for STH from " << log->url() << " for tree size "
+          << unverified_sth.tree_size << " verified.";
+
+  // TODO(eranm): Request a consistency proof.
+  sths_[log_id] = unverified_sth;
+}
+
+}  // namespace certificate_transparency