Mitigate spoofing attempt using Latin letters.

components/url_formatter/idn_spoof_checker.h

Index: components/url_formatter/idn_spoof_checker.h
diff --git a/components/url_formatter/idn_spoof_checker.h b/components/url_formatter/idn_spoof_checker.h
new file mode 100644
index 0000000000000000000000000000000000000000..a1b25e5ce7f8e84ac4ad1ccb1462c42c78915f02
--- /dev/null
+++ b/components/url_formatter/idn_spoof_checker.h
@@ -0,0 +1,68 @@
+// Copyright 2017 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.
+
+// A helper class for IDN Spoof checking, used to ensure that no IDN input is

[Peter Kasting, 2017/05/10 22:38:46]

Nit: Maybe this should be just above the class itself, since that's what it
seems to describe.

[jungshik at Google, 2017/05/14 09:36:23]

Done.

+// spoofable per Chromium's standard of spoofability. For a more thorough
+// explanation of how spoof checking works in Chromium, see
+// http://dev.chromium.org/developers/design-documents/idn-in-google-chrome .
+
+#ifndef COMPONENTS_URL_FORMATTER_IDN_SPOOF_CHECKER_H_
+#define COMPONENTS_URL_FORMATTER_IDN_SPOOF_CHECKER_H_
+
+#include <memory>
+#include <string>
+
+#include "base/strings/string16.h"
+#include "base/strings/string_piece.h"
+#include "third_party/icu/source/common/unicode/uniset.h"
+#include "third_party/icu/source/common/unicode/unistr.h"
+#include "third_party/icu/source/common/unicode/utypes.h"
+#include "third_party/icu/source/i18n/unicode/regex.h"
+#include "third_party/icu/source/i18n/unicode/translit.h"
+#include "third_party/icu/source/i18n/unicode/uspoof.h"

[Peter Kasting, 2017/05/10 22:38:46]

Nit: Seems like most of these #includes are not needed in this header, but only
in the .cc file.  Of the ICU stuff, only UnicodeSet seems like it needs to be
#included; the few other things referenced below can be forward-declared.

[jungshik at Google, 2017/05/14 09:36:23]

Actually, I tried forward declarations before falling back to include headers in
.h file. 

namespace icu {
   class UnicodeString;
   class Transliterator;
.....
...}

does not work because of the way 'icu' is defined. 

However, I forgot that I could use U_ICU_NAMESPACE in place of 'icu'. With that,
forward declaration works. 

Thank you for the comment. 

+
+namespace url_formatter {
+
+class IDNSpoofChecker {
+ public:
+  IDNSpoofChecker();
+  ~IDNSpoofChecker();
+
+  // Returns true if |label| is safe to display as Unicode. In the event of
+  // library failure, all IDN inputs will be treated as unsafe.
+  // See the function body for details on the specific safety checks performed.
+  bool SafeToDisplayAsUnicode(base::StringPiece16 label, bool is_tld_ascii);
+
+  // Returns true if |hostname| or the last few components of |hostname| looks
+  // similar to one of top domains listed in top_domains/alexa_domains.list. Two
+  // checks are done:
+  //   1. Calculate the skeleton of |hostname| based on the Unicode confusable
+  //   character list and look it up in the pre-calculated skeleton list of
+  //   top domains.
+  //   2. Look up the diacritic-free version of |hostname| in the list of
+  //   top domains. Note that non-IDN hostnames will not get here.
+  bool SimilarToTopDomains(base::StringPiece16 hostname);
+
+ private:
+  // Sets allowed characters in IDN labels and turn on USPOOF_CHAR_LIMIT.

[Peter Kasting, 2017/05/10 22:38:46]

Nit: turns

[jungshik at Google, 2017/05/14 09:36:23]

Done.

+  void SetAllowedUnicodeSet(UErrorCode* status);
+  bool IsMadeOfLatinAlikeCyrillic(const icu::UnicodeString& label_string);

[Peter Kasting, 2017/05/10 22:38:46]

Nit: These other two functions don't have comments (probably should) and
definitely should be separated from the function above by a blank line since the
comment above it doesn't also apply to them.

[jungshik at Google, 2017/05/14 09:36:23]

will add desc. 

+  bool GetSkeleton(base::StringPiece16 hostname, std::string* skeleton);
+
+  USpoofChecker* checker_;
+  icu::UnicodeSet deviation_characters_;
+  icu::UnicodeSet non_ascii_latin_letters_;
+  icu::UnicodeSet kana_letters_exceptions_;
+  icu::UnicodeSet combining_diacritics_exceptions_;
+  icu::UnicodeSet cyrillic_letters_;
+  icu::UnicodeSet cyrillic_letters_latin_alike_;
+  icu::UnicodeSet lgc_letters_n_ascii_;
+  std::unique_ptr<icu::Transliterator> transliterator_;
+
+  DISALLOW_COPY_AND_ASSIGN(IDNSpoofChecker);
+};
+
+}  // namespace url_formatter
+
+#endif  // COMPONENTS_URL_FORMATTER_IDN_SPOOF_CHECKER_H_