Add hash to OFC pasteboard change detection

components/open_from_clipboard/clipboard_recent_content_ios.mm

Index: components/open_from_clipboard/clipboard_recent_content_ios.mm
diff --git a/components/open_from_clipboard/clipboard_recent_content_ios.mm b/components/open_from_clipboard/clipboard_recent_content_ios.mm
index d27d2566eb2d3f4b2f893cdbe50c517cd46fbaef..d343f4a723e0fd45a6648d8a1856568087207c4f 100644
--- a/components/open_from_clipboard/clipboard_recent_content_ios.mm
+++ b/components/open_from_clipboard/clipboard_recent_content_ios.mm
@@ -4,6 +4,7 @@
 
 #import "components/open_from_clipboard/clipboard_recent_content_ios.h"
 
+#import <CommonCrypto/CommonDigest.h>
 #import <UIKit/UIKit.h>
 
 #import "base/ios/ios_util.h"
@@ -48,7 +49,7 @@
              object:[UIPasteboard generalPasteboard]];
     [[NSNotificationCenter defaultCenter]
         addObserver:self
-           selector:@selector(pasteboardChangedNotification:)
+           selector:@selector(didBecomeActive:)
                name:UIApplicationDidBecomeActiveNotification
              object:nil];
   }
@@ -66,6 +67,17 @@
   }
 }
 
+- (void)didBecomeActive:(NSNotification*)notification {
+  if (_delegate) {
+    _delegate->LoadFromUserDefaults();
+    base::TimeDelta uptime =
+        base::TimeDelta::FromMilliseconds(base::SysInfo::Uptime());
+    if (_delegate->HasPasteboardChanged(uptime)) {
+      _delegate->PasteboardChanged();
+    }
+  }
+}
+
 - (void)disconnect {
   _delegate = nullptr;
 }
@@ -80,8 +92,12 @@ NSString* kPasteboardChangeCountKey = @"PasteboardChangeCount";
 // Key used to store the last date at which it was detected that the pasteboard
 // changed. It is used to evaluate the age of the pasteboard's content.
 NSString* kPasteboardChangeDateKey = @"PasteboardChangeDate";
-// Key used to store the
-NSString* kSuppressedPasteboardEntryCountKey = @"PasteboardSupressedEntryCount";
+// Key used to store the hash of the content of the pasteboard. Whenever the
+// hash changed, the pasteboard content is considered to have changed.
+NSString* kPasteboardEntryMD5Key = @"PasteboardEntryMD5";
+// Key used to store the date of the latest pasteboard entry displayed in the
+// omnibox. This is used to report metrics on pasteboard change.
+NSString* kLastDisplayedPasteboardEntryKey = @"LastDisplayedPasteboardEntry";
 base::TimeDelta kMaximumAgeOfClipboard = base::TimeDelta::FromHours(3);
 // Schemes accepted by the ClipboardRecentContentIOS.
 const char* kAuthorizedSchemes[] = {
@@ -90,18 +106,29 @@ const char* kAuthorizedSchemes[] = {
     url::kDataScheme,
     url::kAboutScheme,
 };
+
+// Compute a hash consisting of the first 4 bytes of the MD5 hash of |string|.
+// This value is used to detect pasteboard content change. Keeping only 4 bytes
+// is a privacy requirement to introduce collision and allow deniability of
+// having copied a given string.
+NSData* WeakMD5FromNSString(NSString* string) {
+  unsigned char hash[CC_MD5_DIGEST_LENGTH];
+  const char* c_string = [string UTF8String];
+  CC_MD5(c_string, strlen(c_string), hash);
+  NSData* data = [NSData dataWithBytes:hash length:4];
+  return data;
+}
+
 }  // namespace
 
 bool ClipboardRecentContentIOS::GetRecentURLFromClipboard(GURL* url) const {
   DCHECK(url);
-  if (GetClipboardContentAge() > kMaximumAgeOfClipboard ||
-      [UIPasteboard generalPasteboard].changeCount ==
-          suppressedPasteboardEntryCount_) {
+  if (GetClipboardContentAge() > kMaximumAgeOfClipboard) {
     return false;
   }
 
-  if (urlFromPasteboardCache_.is_valid()) {
-    *url = urlFromPasteboardCache_;
+  if (url_from_pasteboard_cache_.is_valid()) {
+    *url = url_from_pasteboard_cache_;
     return true;
   }
   return false;
@@ -109,81 +136,90 @@ bool ClipboardRecentContentIOS::GetRecentURLFromClipboard(GURL* url) const {
 
 base::TimeDelta ClipboardRecentContentIOS::GetClipboardContentAge() const {
   return base::TimeDelta::FromSeconds(
-      static_cast<int64>(-[lastPasteboardChangeDate_ timeIntervalSinceNow]));
+      static_cast<int64>(-[last_pasteboard_change_date_ timeIntervalSinceNow]));
 }
 
 void ClipboardRecentContentIOS::SuppressClipboardContent() {
-  suppressedPasteboardEntryCount_ =
-      [UIPasteboard generalPasteboard].changeCount;
+  // User cleared the user data. The pasteboard entry must be removed from the
+  // omnibox list. Force entry expiration by setting copy date to 1970.
+  last_pasteboard_change_date_.reset(
+      [[NSDate alloc] initWithTimeIntervalSince1970:0]);
   SaveToUserDefaults();
 }
 
 void ClipboardRecentContentIOS::PasteboardChanged() {
-  urlFromPasteboardCache_ = URLFromPasteboard();
-  if (!urlFromPasteboardCache_.is_empty()) {
+  url_from_pasteboard_cache_ = URLFromPasteboard();
+  if (!url_from_pasteboard_cache_.is_empty()) {
     base::RecordAction(
         base::UserMetricsAction("MobileOmniboxClipboardChanged"));
   }
-  lastPasteboardChangeDate_.reset([[NSDate date] retain]);
-  lastPasteboardChangeCount_ = [UIPasteboard generalPasteboard].changeCount;
-  if (lastPasteboardChangeCount_ != suppressedPasteboardEntryCount_) {
-    suppressedPasteboardEntryCount_ = NSIntegerMax;
+  last_pasteboard_change_date_.reset([[NSDate date] retain]);
+  last_pasteboard_change_count_ = [UIPasteboard generalPasteboard].changeCount;
+  NSString* pasteboard_string = [[UIPasteboard generalPasteboard] string];
+  if (!pasteboard_string) {
+    pasteboard_string = @"";
   }
+  NSData* MD5 = WeakMD5FromNSString(pasteboard_string);
+  last_pasteboard_entry_md5_.reset([MD5 retain]);
+  SaveToUserDefaults();
 }
 
 ClipboardRecentContentIOS::ClipboardRecentContentIOS(
-    const std::string& application_scheme)
-    : application_scheme_(application_scheme) {
+    const std::string& application_scheme,
+    NSUserDefaults* group_user_defaults)
+    : application_scheme_(application_scheme),
+      shared_user_defaults_([group_user_defaults retain]) {
   Init(base::TimeDelta::FromMilliseconds(base::SysInfo::Uptime()));
 }
 
 ClipboardRecentContentIOS::ClipboardRecentContentIOS(
     const std::string& application_scheme,
     base::TimeDelta uptime)
-    : application_scheme_(application_scheme) {
+    : application_scheme_(application_scheme),
+      shared_user_defaults_([[NSUserDefaults standardUserDefaults] retain]) {
   Init(uptime);
 }
 
+bool ClipboardRecentContentIOS::HasPasteboardChanged(base::TimeDelta uptime) {
+  NSInteger change_count = [UIPasteboard generalPasteboard].changeCount;
+  bool change_count_changed = change_count != last_pasteboard_change_count_;
+
+  bool not_rebooted = uptime > GetClipboardContentAge();

[droger, 2015/08/13 11:42:21]

Optional: should we early return here if (not_rebooted && change_count_changed)?

[Olivier, 2015/08/13 12:01:58]

Done.

[Olivier, 2015/08/13 12:01:58]

Done.

+
+  NSString* pasteboard_string = [[UIPasteboard generalPasteboard] string];
+  if (!pasteboard_string) {
+    pasteboard_string = @"";
+  }
+  NSData* md5 = WeakMD5FromNSString(pasteboard_string);
+  BOOL md5_changed = ![md5 isEqualToData:last_pasteboard_entry_md5_];

[droger, 2015/08/13 11:42:21]

What happens if there is a collision? Is this a privacy issue?

[droger, 2015/08/13 11:51:52]

Resolved by offline discussion: hash collisions are not a privacy issue and
covered by the design.

+
+  // If |MD5Changed|, we know for sure there has been at least one pasteboard
+  // copy since last time it was checked.
+  // If the pasteboard content is still the same but the device was not
+  // rebooted, the change count can be checked to see if it changed.
+  // Note: due to a mismatch between the actual behavior and documentation, and
+  // lack of consistency on different reboot scenarios, the change count cannot
+  // be checked after a reboot.
+  // See radar://21833556 for more information.
+  return md5_changed || (not_rebooted && change_count_changed);
+}
+
 void ClipboardRecentContentIOS::Init(base::TimeDelta uptime) {
-  lastPasteboardChangeCount_ = NSIntegerMax;
-  suppressedPasteboardEntryCount_ = NSIntegerMax;
-  urlFromPasteboardCache_ = URLFromPasteboard();
+  last_pasteboard_change_count_ = NSIntegerMax;
+  url_from_pasteboard_cache_ = URLFromPasteboard();
   LoadFromUserDefaults();
 
-  // On iOS 7 (unlike on iOS 8, despite what the documentation says), the change
-  // count is reset when the device is rebooted.
-  if (uptime < GetClipboardContentAge() &&
-      !base::ios::IsRunningOnIOS8OrLater()) {
-    if ([UIPasteboard generalPasteboard].changeCount == 0) {
-      // The user hasn't pasted anything in the clipboard since the device's
-      // reboot. |PasteboardChanged| isn't called because it would update
-      // |lastPasteboardChangeData_|, and record metrics.
-      lastPasteboardChangeCount_ = 0;
-      if (suppressedPasteboardEntryCount_ != NSIntegerMax) {
-        // If the last time Chrome was running the pasteboard was suppressed,
-        // and the user  has not copied anything since the device launched, then
-        // supress this entry.
-        suppressedPasteboardEntryCount_ = 0;
-      }
-      SaveToUserDefaults();
-    } else {
-      // The user pasted something in the clipboard since the device's reboot.
-      PasteboardChanged();
-    }
-  } else {
-    NSInteger changeCount = [UIPasteboard generalPasteboard].changeCount;
-    if (changeCount != lastPasteboardChangeCount_) {
-      PasteboardChanged();
-    }
-  }
-  // Makes sure |lastPasteboardChangeCount_| was properly initialized.
-  DCHECK_NE(lastPasteboardChangeCount_, NSIntegerMax);
-  notificationBridge_.reset(
+  if (HasPasteboardChanged(uptime))
+    PasteboardChanged();
+
+  // Makes sure |last_pasteboard_change_count_| was properly initialized.
+  DCHECK_NE(last_pasteboard_change_count_, NSIntegerMax);
+  notification_bridge_.reset(
       [[PasteboardNotificationListenerBridge alloc] initWithDelegate:this]);
 }
 
 ClipboardRecentContentIOS::~ClipboardRecentContentIOS() {
-  [notificationBridge_ disconnect];
+  [notification_bridge_ disconnect];
 }
 
 GURL ClipboardRecentContentIOS::URLFromPasteboard() {
@@ -204,32 +240,37 @@ GURL ClipboardRecentContentIOS::URLFromPasteboard() {
   return GURL::EmptyGURL();
 }
 
-void ClipboardRecentContentIOS::LoadFromUserDefaults() {
-  NSUserDefaults* defaults = [NSUserDefaults standardUserDefaults];
-
-  lastPasteboardChangeCount_ =
-      [defaults integerForKey:kPasteboardChangeCountKey];
-  lastPasteboardChangeDate_.reset(
-      [[defaults objectForKey:kPasteboardChangeDateKey] retain]);
-
-  if ([[[defaults dictionaryRepresentation] allKeys]
-          containsObject:kSuppressedPasteboardEntryCountKey]) {
-    suppressedPasteboardEntryCount_ =
-        [defaults integerForKey:kSuppressedPasteboardEntryCountKey];
-  } else {
-    suppressedPasteboardEntryCount_ = NSIntegerMax;
+void ClipboardRecentContentIOS::RecentURLDisplayed() {
+  if ([last_pasteboard_change_date_
+          isEqualToDate:last_displayed_pasteboard_entry_.get()]) {
+    return;
   }
+  base::RecordAction(base::UserMetricsAction("MobileOmniboxClipboardChanged"));
+  last_pasteboard_change_date_ = last_displayed_pasteboard_entry_;
+  SaveToUserDefaults();
+}
+
+void ClipboardRecentContentIOS::LoadFromUserDefaults() {
+  last_pasteboard_change_count_ =
+      [shared_user_defaults_ integerForKey:kPasteboardChangeCountKey];
+  last_pasteboard_change_date_.reset(
+      [[shared_user_defaults_ objectForKey:kPasteboardChangeDateKey] retain]);
+  last_pasteboard_entry_md5_.reset(
+      [[shared_user_defaults_ objectForKey:kPasteboardEntryMD5Key] retain]);
+  last_displayed_pasteboard_entry_.reset([[shared_user_defaults_
+      objectForKey:kLastDisplayedPasteboardEntryKey] retain]);
 
-  DCHECK(!lastPasteboardChangeDate_ ||
-         [lastPasteboardChangeDate_ isKindOfClass:[NSDate class]]);
+  DCHECK(!last_pasteboard_change_date_ ||
+         [last_pasteboard_change_date_ isKindOfClass:[NSDate class]]);
 }
 
 void ClipboardRecentContentIOS::SaveToUserDefaults() {
-  NSUserDefaults* defaults = [NSUserDefaults standardUserDefaults];
-  [defaults setInteger:lastPasteboardChangeCount_
-                forKey:kPasteboardChangeCountKey];
-  [defaults setObject:lastPasteboardChangeDate_
-               forKey:kPasteboardChangeDateKey];
-  [defaults setInteger:suppressedPasteboardEntryCount_
-                forKey:kSuppressedPasteboardEntryCountKey];
+  [shared_user_defaults_ setInteger:last_pasteboard_change_count_
+                             forKey:kPasteboardChangeCountKey];
+  [shared_user_defaults_ setObject:last_pasteboard_change_date_
+                            forKey:kPasteboardChangeDateKey];
+  [shared_user_defaults_ setObject:last_pasteboard_entry_md5_
+                            forKey:kPasteboardEntryMD5Key];
+  [shared_user_defaults_ setObject:last_displayed_pasteboard_entry_
+                            forKey:kLastDisplayedPasteboardEntryKey];
 }