Private API for extensions like ssh-client that need access to TCP.

chrome/browser/internal_auth.cc

+// Copyright (c) 2011 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 "chrome/browser/internal_auth.h"
+
+#include <algorithm>
+#include <deque>
+
+#include "base/base64.h"
+#include "base/lazy_instance.h"
+#include "base/rand_util.h"
+#include "base/synchronization/lock.h"
+#include "base/string_number_conversions.h"
+#include "base/string_split.h"
+#include "base/string_util.h"
+#include "base/threading/thread_checker.h"
+#include "base/time.h"
+#include "base/timer.h"
+#include "base/values.h"
+#include "content/browser/browser_thread.h"
+#include "crypto/hmac.h"
+
+namespace {
+
+typedef std::map<std::string, std::string> VarValueMap;
+
+// Size of a tick in microseconds. This determines upper bound for average
+// number of passports generated per time unit. This bound equals to
+// (kMicrosecondsPerSecond / TickUs) calls per second.
+const int64 kTickUs = 10000;
+
+// Verification window size in ticks; that means any passport expires in
+// (kVerificationWindowTicks * TickUs / kMicrosecondsPerSecond) seconds.
+const int kVerificationWindowTicks = 2000;
+
+// Generation window determines how well we are able to cope with bursts of
+// GeneratePassport calls those exceed upper bound on average speed.
+const int kGenerationWindowTicks = 20;
+
+// Makes no sense to compare other way round.
+COMPILE_ASSERT(kGenerationWindowTicks <= kVerificationWindowTicks,
+    makes_no_sense_to_have_generation_window_larger_than_verification_one);
+// We are not optimized for high value of kGenerationWindowTicks.
+COMPILE_ASSERT(kGenerationWindowTicks < 30, too_large_generation_window);
+
+// Regenerate key after this number of ticks.
+const int kKeyRegenerationSoftTicks = 500000;
+// Reject passports if key has not been regenerated in that number of ticks.
+const int kKeyRegenerationHardTicks = kKeyRegenerationSoftTicks * 2;
+
+// Limit for number of accepted var=value pairs. Feel free to bump this limit
+// higher once needed.
+const size_t kVarsLimit = 16;
+
+// Limit for length of caller-supplied strings. Feel free to bump this limit
+// higher once needed.
+const size_t kStringLengthLimit = 512;
+
+// Character used as a separator for construction of message to take HMAC of.
+// It is critical to validate all caller-supplied data (used to construct
+// message) to be clear of this separator because it could allow attacks.
+const char kItemSeparator = '\n';
+
+// Character used for var=value separation.
+const char kVarValueSeparator = '=';
+
+const size_t kKeySizeInBytes = 128 / 8;
+const int kHMACSizeInBytes = 256 / 8;
+
+// Length of base64 string required to encode given number of raw octets.
+#define BASE64_PER_RAW(X) (X > 0 ? ((X - 1) / 3 + 1) * 4 : 0)
+
+// Size of decimal string representing 64-bit tick.
+const size_t kTickStringLength = 20;
+
+// A passport consists of 2 parts: HMAC and tick.
+const size_t kPassportSize =
+    BASE64_PER_RAW(kHMACSizeInBytes) + kTickStringLength;
+
+int64 GetCurrentTick() {
+  int64 tick = base::Time::Now().ToInternalValue() / kTickUs;
+  if (tick < kVerificationWindowTicks ||
+      tick < kKeyRegenerationHardTicks ||
+      tick > kint64max - kKeyRegenerationHardTicks) {
+    return 0;
+  }
+  return tick;
+}
+
+bool IsDomainSane(const std::string& domain) {
+  return !domain.empty() &&
+      domain.size() <= kStringLengthLimit &&
+      IsStringUTF8(domain) &&
+      domain.find_first_of(kItemSeparator) == std::string::npos;
+}
+
+bool IsVarSane(const std::string& var) {
+  static const char kAllowedChars[] =
+      "ABCDEFGHIJKLMNOPQRSTUVWXYZ"
+      "abcdefghijklmnopqrstuvwxyz"
+      "0123456789"
+      "_";
+  COMPILE_ASSERT(
+      sizeof(kAllowedChars) == 26 + 26 + 10 + 1 + 1, some_mess_with_chars);
+  // We must not allow kItemSeparator in anything used as an input to construct
+  // message to sign.
+  DCHECK(std::find(kAllowedChars, kAllowedChars + arraysize(kAllowedChars),
+      kItemSeparator) == kAllowedChars + arraysize(kAllowedChars));
+  DCHECK(std::find(kAllowedChars, kAllowedChars + arraysize(kAllowedChars),
+      kVarValueSeparator) == kAllowedChars + arraysize(kAllowedChars));
+  return !var.empty() &&
+      var.size() <= kStringLengthLimit &&
+      IsStringASCII(var) &&
+      var.find_first_not_of(kAllowedChars) == std::string::npos &&
+      !IsAsciiDigit(var[0]);
+}
+
+bool IsValueSane(const std::string& value) {
+  return value.size() <= kStringLengthLimit &&
+      IsStringUTF8(value) &&
+      value.find_first_of(kItemSeparator) == std::string::npos;
+}
+
+bool IsVarValueMapSane(const VarValueMap& map) {
+  if (map.size() > kVarsLimit)
+    return false;
+  for (VarValueMap::const_iterator it = map.begin(); it != map.end(); ++it) {
+    const std::string& var = it->first;
+    const std::string& value = it->second;
+    if (!IsVarSane(var) || !IsValueSane(value))
+      return false;
+  }
+  return true;
+}
+
+void ConvertVarValueMapToBlob(const VarValueMap& map, std::string* out) {
+  out->clear();
+  DCHECK(IsVarValueMapSane(map));
+  for (VarValueMap::const_iterator it = map.begin(); it != map.end(); ++it)
+    *out += it->first + kVarValueSeparator + it->second + kItemSeparator;
+}
+
+void CreatePassport(
+    const std::string& domain,
+    const VarValueMap& map,
+    int64 tick,
+    const crypto::HMAC* engine,
+    std::string* out) {
+  DCHECK(engine);
+  DCHECK(out);
+  DCHECK(IsDomainSane(domain));
+  DCHECK(IsVarValueMapSane(map));
+
+  out->clear();
+  std::string result(kPassportSize, '0');
+
+  std::string blob;
+  blob = domain + kItemSeparator;
+  std::string tmp;
+  ConvertVarValueMapToBlob(map, &tmp);
+  blob += tmp + kItemSeparator + base::Uint64ToString(tick);
+
+  std::string hmac;
+  unsigned char* hmac_data = reinterpret_cast<unsigned char*>(
+      WriteInto(&hmac, kHMACSizeInBytes + 1));
+  if (!engine->Sign(blob, hmac_data, kHMACSizeInBytes)) {
+    NOTREACHED();
+    return;
+  }
+  std::string hmac_base64;
+  if (!base::Base64Encode(hmac, &hmac_base64)) {
+    NOTREACHED();
+    return;
+  }
+  if (hmac_base64.size() != BASE64_PER_RAW(kHMACSizeInBytes)) {
+    NOTREACHED();
+    return;
+  }
+  DCHECK(hmac_base64.size() < result.size());
+  std::copy(hmac_base64.begin(), hmac_base64.end(), result.begin());
+
+  std::string tick_decimal = base::Uint64ToString(tick);
+  DCHECK(tick_decimal.size() <= kTickStringLength);
+  std::copy(
+      tick_decimal.begin(),
+      tick_decimal.end(),
+      result.begin() + kPassportSize - tick_decimal.size());
+
+  out->swap(result);
+}
+
+}  // namespace
+
+namespace browser {
+
+class InternalAuthVerificationService {
+ public:
+  InternalAuthVerificationService()
+      : key_change_tick_(0),
+        dark_tick_(0) {
+  }
+
+  bool VerifyPassport(
+      const std::string& passport,
+      const std::string& domain,
+      const VarValueMap& map) {
+    int64 current_tick = GetCurrentTick();
+    int64 tick = PreVerifyPassport(passport, domain, current_tick);
+    if (tick == 0)
+      return false;
+    if (!IsVarValueMapSane(map))
+      return false;
+    std::string reference_passport;
+    CreatePassport(domain, map, tick, engine_.get(), &reference_passport);
+    if (passport != reference_passport) {
+      // Consider old key.
+      if (key_change_tick_ + get_verification_window_ticks() < tick) {
+        return false;
+      }
+      if (old_key_.empty() || old_engine_ == NULL)
+        return false;
+      CreatePassport(domain, map, tick, old_engine_.get(), &reference_passport);
+      if (passport != reference_passport)
+        return false;
+    }
+
+    // Record used tick to prevent reuse.
+    std::deque<int64>::iterator it = std::lower_bound(
+        used_ticks_.begin(), used_ticks_.end(), tick);
+    DCHECK(it == used_ticks_.end() || *it != tick);
+    used_ticks_.insert(it, tick);
+
+    // Consider pruning |used_ticks_|.
+    if (used_ticks_.size() > 50) {
+      dark_tick_ = std::max(dark_tick_,
+          current_tick - get_verification_window_ticks());
+      used_ticks_.erase(
+          used_ticks_.begin(),
+          std::lower_bound(used_ticks_.begin(), used_ticks_.end(),
+                           dark_tick_ + 1));
+    }
+    return true;
+  }
+
+  void ChangeKey(const std::string& key) {
+    old_key_.swap(key_);
+    key_.clear();
+    old_engine_.swap(engine_);
+    engine_.reset(NULL);
+
+    if (key.size() != kKeySizeInBytes)
+      return;
+    engine_.reset(new crypto::HMAC(crypto::HMAC::SHA256));
+    engine_->Init(key);
+    key_ = key;
+    key_change_tick_ = GetCurrentTick();
+  }
+
+ private:
+  static int get_verification_window_ticks() {
+    return InternalAuthVerification::get_verification_window_ticks();
+  }
+
+  // Returns tick bound to given passport on success or zero on failure.
+  int64 PreVerifyPassport(
+    const std::string& passport,
+    const std::string& domain,
+    int64 current_tick) {
+    if (passport.size() != kPassportSize ||
+        !IsStringASCII(passport) ||
+        !IsDomainSane(domain) ||
+        current_tick <= dark_tick_ ||
+        current_tick > key_change_tick_  + kKeyRegenerationHardTicks ||
+        key_.empty() ||
+        engine_ == NULL) {
+      return 0;
+    }
+
+    // Passport consists of 2 parts: first hmac and then tick.
+    std::string tick_decimal =
+        passport.substr(BASE64_PER_RAW(kHMACSizeInBytes));
+    DCHECK(tick_decimal.size() == kTickStringLength);
+    int64 tick = 0;
+    if (!base::StringToInt64(tick_decimal, &tick) ||
+        tick <= dark_tick_ ||
+        tick > key_change_tick_ + kKeyRegenerationHardTicks ||
+        tick < current_tick - get_verification_window_ticks() ||
+        std::binary_search(used_ticks_.begin(), used_ticks_.end(), tick)) {
+      return 0;
+    }
+    return tick;
+  }
+
+  // Current key.
+  std::string key_;
+
+  // We keep previous key in order to be able to verify passports during
+  // regeneration time.  Keys are regenerated on a regular basis.
+  std::string old_key_;
+
+  // Corresponding HMAC engines.
+  scoped_ptr<crypto::HMAC> engine_;
+  scoped_ptr<crypto::HMAC> old_engine_;
+
+  // Tick at a time of recent key regeneration.
+  int64 key_change_tick_;
+
+  // Keeps track of ticks of successfully verified passports to prevent their
+  // reuse. Size of this container is kept reasonably low by purging outdated
+  // ticks.
+  std::deque<int64> used_ticks_;
+
+  // Some ticks before |dark_tick_| were purged from |used_ticks_| container.
+  // That means that we must not trust any tick less than or equal to dark tick.
+  int64 dark_tick_;
+
+  DISALLOW_COPY_AND_ASSIGN(InternalAuthVerificationService);
+};
+
+}  // namespace browser
+
+namespace {
+
+static base::LazyInstance<browser::InternalAuthVerificationService>
+    g_verification_service(base::LINKER_INITIALIZED);
+static base::LazyInstance<base::Lock> g_verification_service_lock(
+    base::LINKER_INITIALIZED);
+
+}  // namespace
+
+namespace browser {
+
+class InternalAuthGenerationService : public base::ThreadChecker {
+ public:
+  InternalAuthGenerationService() : key_regeneration_tick_(0) {
+    GenerateNewKey();
+  }
+
+  void GenerateNewKey() {
+    DCHECK(CalledOnValidThread());
+    if (!timer_.IsRunning()) {
+      timer_.Start(
+          base::TimeDelta::FromMicroseconds(
+              kKeyRegenerationSoftTicks * kTickUs),
+          this,
+          &InternalAuthGenerationService::GenerateNewKey);
+    }
+
+    engine_.reset(new crypto::HMAC(crypto::HMAC::SHA256));
+    std::string key = base::RandBytesAsString(kKeySizeInBytes);
+    engine_->Init(key);
+    key_regeneration_tick_ = GetCurrentTick();
+    g_verification_service.Get().ChangeKey(key);
+    std::fill(key.begin(), key.end(), 0);
+  }
+
+  // Returns zero on failure.
+  int64 GetUnusedTick(const std::string& domain) {
+    DCHECK(CalledOnValidThread());
+    if (engine_ == NULL) {
+      NOTREACHED();
+      return 0;
+    }
+    if (!IsDomainSane(domain))
+      return 0;
+
+    int64 current_tick = GetCurrentTick();
+    if (!used_ticks_.empty() && used_ticks_.back() > current_tick)
+      current_tick = used_ticks_.back();
+    if (current_tick > key_regeneration_tick_ + kKeyRegenerationHardTicks)
+      return 0;
+
+    // Forget outdated ticks if any.
+    used_ticks_.erase(
+        used_ticks_.begin(),
+        std::lower_bound(used_ticks_.begin(), used_ticks_.end(),
+                         current_tick - kGenerationWindowTicks + 1));
+    DCHECK(used_ticks_.size() <= kGenerationWindowTicks + 0u);
+    if (used_ticks_.size() >= kGenerationWindowTicks + 0u) {
+      // Average speed of GeneratePassport calls exceeds limit.
+      return 0;
+    }
+    for (int64 tick = current_tick;
+        tick > current_tick - kGenerationWindowTicks;
+        --tick) {
+      int idx = static_cast<int>(used_ticks_.size()) -
+          static_cast<int>(current_tick - tick + 1);
+      if (idx < 0 || used_ticks_[idx] != tick) {
+        DCHECK(used_ticks_.end() ==
+            std::find(used_ticks_.begin(), used_ticks_.end(), tick));
+        return tick;
+      }
+    }
+    NOTREACHED();
+    return 0;
+  }
+
+  std::string GeneratePassport(
+      const std::string& domain, const VarValueMap& map, int64 tick) {
+    DCHECK(CalledOnValidThread());
+    if (tick == 0) {
+      tick = GetUnusedTick(domain);
+      if (tick == 0)
+        return std::string();
+    }
+    if (!IsVarValueMapSane(map))
+      return std::string();
+
+    std::string result;
+    CreatePassport(domain, map, tick, engine_.get(), &result);
+    used_ticks_.insert(
+        std::lower_bound(used_ticks_.begin(), used_ticks_.end(), tick), tick);
+    return result;
+  }
+
+ private:
+  static int get_verification_window_ticks() {
+    return InternalAuthVerification::get_verification_window_ticks();
+  }
+
+  scoped_ptr<crypto::HMAC> engine_;
+  base::RepeatingTimer<InternalAuthGenerationService> timer_;
+  int64 key_regeneration_tick_;
+  std::deque<int64> used_ticks_;
+
+  DISALLOW_COPY_AND_ASSIGN(InternalAuthGenerationService);
+};
+
+}  // namespace browser
+
+namespace {
+
+static base::LazyInstance<browser::InternalAuthGenerationService>
+    g_generation_service(base::LINKER_INITIALIZED);
+
+}  // namespace
+
+namespace browser {
+
+// static
+bool InternalAuthVerification::VerifyPassport(
+    const std::string& passport,
+    const std::string& domain,
+    const VarValueMap& var_value_map) {
+  base::AutoLock alk(g_verification_service_lock.Get());
+  return g_verification_service.Get().VerifyPassport(
+      passport, domain, var_value_map);
+}
+
+// static
+void InternalAuthVerification::ChangeKey(const std::string& key) {
+  base::AutoLock alk(g_verification_service_lock.Get());
+  g_verification_service.Get().ChangeKey(key);
+};
+
+// static
+int InternalAuthVerification::get_verification_window_ticks() {
+  int candidate = kVerificationWindowTicks;
+  if (verification_window_seconds_ > 0)
+    candidate = verification_window_seconds_ *
+        base::Time::kMicrosecondsPerSecond / kTickUs;
+  return std::max(1, std::min(candidate, kVerificationWindowTicks));
+}
+
+int InternalAuthVerification::verification_window_seconds_ = 0;
+
+// static
+std::string InternalAuthGeneration::GeneratePassport(
+    const std::string& domain, const VarValueMap& var_value_map) {
+  return g_generation_service.Get().GeneratePassport(domain, var_value_map, 0);
+}
+
+// static
+void InternalAuthGeneration::GenerateNewKey() {
+  g_generation_service.Get().GenerateNewKey();
+}
+
+}  // namespace browser
+