Allow empty keys in hmac_openssl.cc.

crypto/hmac_unittest.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 <string>
 
 #include "crypto/hmac.h"
 #include "testing/gtest/include/gtest/gtest.h"
 
 static const size_t kSHA1DigestSize = 20;
@@ skipping 257 matching lines @@
         base::StringPiece(kSimpleHmacCases[i].data,
                           kSimpleHmacCases[i].data_len)));
 
     // Expected size, mismatched data
     EXPECT_FALSE(hmac.Verify(
         base::StringPiece(kSimpleHmacCases[i].data,
                           kSimpleHmacCases[i].data_len),
         base::StringPiece(empty_digest, kSHA1DigestSize)));
   }
 }
+
+TEST(HMACTest, EmptyKey) {
+  // Test vector from https://en.wikipedia.org/wiki/HMAC
+  const char* kExpectedDigest =
+      "\xFB\xDB\x1D\x1B\x18\xAA\x6C\x08\x32\x4B\x7D\x64\xB7\x1F\xB7\x63"
+      "\x70\x69\x0E\x1D";
+
+  crypto::HMAC hmac(crypto::HMAC::SHA1);
+  ASSERT_TRUE(hmac.Init(NULL, 0));
+
+  unsigned char digest[kSHA1DigestSize];
+  EXPECT_TRUE(hmac.Sign("", digest, kSHA1DigestSize));

[wtc, 2014/04/09 21:30:58]

Please use base::StringPiece() instead of "" here and in the hmac.Verify() call,
to eliminate the doubt that the null terminator in an empty C string may get
used.

[davidben, 2014/04/09 21:44:29]

Done. Amusingly, I had to use base::StringPiece("", 0) rather than
base::StringPiece(NULL, 0). The latter upsets NSS. I think I have to conclude C
code by and large doesn't deal with empty byte arrays very well. :-)

+  EXPECT_EQ(0, memcmp(kExpectedDigest, digest, kSHA1DigestSize));
+
+  EXPECT_TRUE(hmac.Verify(
+      "", base::StringPiece(kExpectedDigest, kSHA1DigestSize)));
+}