Only store leading 13 bits of password hash.

chrome/browser/signin/local_auth_unittest.cc

 // Copyright 2013 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/signin/local_auth.h"
 
 #include "base/base64.h"
 #include "base/prefs/pref_service.h"
 #include "chrome/browser/profiles/profile_manager.h"
 #include "chrome/test/base/testing_browser_process.h"
@@ skipping 38 matching lines @@
   base::Base64Decode(passhash.substr(1), &decodedhash);
   EXPECT_FALSE(decodedhash.empty());
   EXPECT_EQ(decodedhash.find(password), std::string::npos);
 
   EXPECT_TRUE(ValidateLocalAuthCredentials(prof, password));
   EXPECT_FALSE(ValidateLocalAuthCredentials(prof, password + "1"));
 
   SetLocalAuthCredentials(prof, password);  // makes different salt
   EXPECT_NE(passhash, cache.GetLocalAuthCredentialsOfProfileAtIndex(0));
 }
+
+TEST(LocalAuthTest, TruncateStringTo16Bits) {
+  std::string two_chars = "AB";

[jww, 2015/01/22 21:48:18]

It seems like you might want these tests to actually be of
ValidateLocalAuthCredentials since that's the more public API (and
TruncateStringTo16Bits is used by that function exclusively anyway).

[Mike Lerman, 2015/01/27 21:02:26]

TruncateStringTo16Bit was a tricky method to write and I really want to have
unit tests that are specific to it. It would be hard to unit test it effectively
through only calling ValidateLocalAuthCredentials.

I can additionally make unit tests for ValidateLocalAuthCredentials if you see a
need, although the flow's already tested above.

+  std::string three_chars = "ABC";
+  EXPECT_EQ(two_chars, TruncateStringByBits(two_chars, 16));
+  EXPECT_EQ(two_chars, TruncateStringByBits(three_chars, 16));
+}
+
+TEST(LocalAuthTest, TruncateStringTo14BitsLowBitsOnly) {
+  std::string two_chars = "A6";
+  std::string three_chars = "A6C";
+  EXPECT_EQ(two_chars, TruncateStringByBits(two_chars, 14));
+  EXPECT_EQ(two_chars, TruncateStringByBits(three_chars, 14));
+}
+
+TEST(LocalAuthTest, TruncateStringTo14BitsLowAndHighBits) {
+  std::string two_chars = "Az";
+  std::string three_chars = "AzC";
+  // 'z' = 0x7A, ':' = 0x3A.
+  std::string two_chars_truncated = "A:";
+  EXPECT_EQ(two_chars_truncated, TruncateStringByBits(two_chars, 14));
+  EXPECT_EQ(two_chars_truncated, TruncateStringByBits(three_chars, 14));
+}