Only store leading 13 bits of password hash.

chrome/browser/signin/local_auth_unittest.cc

Index: chrome/browser/signin/local_auth_unittest.cc
diff --git a/chrome/browser/signin/local_auth_unittest.cc b/chrome/browser/signin/local_auth_unittest.cc
index 68ee397043ad9c9614b444ad6611043eda24453d..e0a59b39af9ddac49b71ae85fd299226a4b40367 100644
--- a/chrome/browser/signin/local_auth_unittest.cc
+++ b/chrome/browser/signin/local_auth_unittest.cc
@@ -56,3 +56,26 @@ TEST(LocalAuthTest, SetAndCheckCredentials) {
   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));
+}