Fix nits in SecureHash.

crypto/secure_hash_default.cc

 // Copyright (c) 2012 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 "crypto/secure_hash.h"
 
 #include "base/logging.h"
 #include "base/pickle.h"
 #include "crypto/third_party/nss/chromium-blapi.h"
 #include "crypto/third_party/nss/chromium-sha256.h"
 
 namespace crypto {
 
 namespace {
 
 const char kSHA256Descriptor[] = "NSS";
 
 class SecureHashSHA256NSS : public SecureHash {
  public:
   static const int kSecureHashVersion = 1;
 
   SecureHashSHA256NSS() {
     SHA256_Begin(&ctx_);
   }
 
   virtual ~SecureHashSHA256NSS() {
+    memset(&ctx_, 0, sizeof(ctx_));

[wtc, 2012/11/28 20:49:30]

This matches what the SecureHashSHA256OpenSSL destructor does:

  virtual ~SecureHashSHA256OpenSSL() {
    OPENSSL_cleanse(&ctx_, sizeof(ctx_));
  }

[agl, 2012/11/28 21:25:30]

I believe that there is a significant chance that compilers will remove this:
http://www.viva64.com/en/b/0178/

[Ryan Sleevi, 2012/11/28 22:17:08]

Agreed. It's gonna be a nop on -O2 and higher.

See
http://cwe.mitre.org/data/definitions/14.html

[wtc, 2012/11/28 22:39:36]

Thanks for pointing this out. We should add a function to
src/base or NSS to do this.

OPENSSL_cleanse seems to rely on the use of a global variable
(cleanse_ctr in crypto/mem_clr.c) to make the compiler think
the function cannot be optimized away. I wonder if there is
another simple way to prevent compiler from removing the
function call. (On Windows we can just call the Windows
SecureZeroMemory function.)

   }
 
   // SecureHash implementation:
   virtual void Update(const void* input, size_t len) OVERRIDE {
     SHA256_Update(&ctx_, static_cast<const unsigned char*>(input), len);
   }
 
   virtual void Finish(void* output, size_t len) OVERRIDE {
     SHA256_End(&ctx_, static_cast<unsigned char*>(output), NULL,
                static_cast<unsigned int>(len));
@@ skipping 49 matching lines @@
   switch (algorithm) {
     case SHA256:
       return new SecureHashSHA256NSS();
     default:
       NOTIMPLEMENTED();
       return NULL;
   }
 }
 
 }  // namespace crypto