Implement AES-CTR for NSS.

crypto/encryptor.h

 // 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.
 
 #ifndef CRYPTO_ENCRYPTOR_H_
 #define CRYPTO_ENCRYPTOR_H_
 #pragma once
 
 #include <string>
 
+#include "base/basictypes.h"
+#include "base/scoped_ptr.h"
 #include "build/build_config.h"
-
 #if defined(USE_NSS)
 #include "crypto/scoped_nss_types.h"
 #elif defined(OS_WIN)
 #include "crypto/scoped_capi_types.h"
 #endif
 
 namespace crypto {
 
 class SymmetricKey;
 
 class Encryptor {
  public:
   enum Mode {
-    CBC
+    CBC,
+    CTR,
   };
+
+  // This class implements a 128-bits counter to be used in AES-CTR encryption.
+  // Only 128-bits counter is supported in this class.
+  class Counter {
+   public:
+    Counter(const std::string& counter);

[wtc, 2011/06/21 00:33:32]

To match PKCS #11's CK_AES_CTR_PARAMS structure, the
constructor should also take a
  size_t counter_bits
input argument, to indicate the number of bits in 'counter'
that shall be incremented.  The counter bits are the least
significant bits of the counter block.

In general 0 < counter_bits <= 128, but you should add
  CHECK_EQ(counter_bits, 128);

+    ~Counter();
+
+    // Increment the counter value.
+    void Increment();
+
+    // Write the content of the counter to |buf|. |buf| should have enough
+    // space for |GetLengthInBytes()|.
+    void Write(void* buf);
+
+    // Return the length of this counter.
+    size_t GetLengthInBytes() const;
+
+   private:
+    uint64 high_num_;
+    uint64 low_num_;
+  };
+
   Encryptor();
   virtual ~Encryptor();
 
   // Initializes the encryptor using |key| and |iv|. Returns false if either the
   // key or the initialization vector cannot be used.
+  //
+  // When |mode| is CTR then |iv| should be empty.

[wtc, 2011/06/21 00:33:32]

Nit: When => If

   bool Init(SymmetricKey* key, Mode mode, const std::string& iv);
 
   // Encrypts |plaintext| into |ciphertext|.
   bool Encrypt(const std::string& plaintext, std::string* ciphertext);
 
   // Decrypts |ciphertext| into |plaintext|.
   bool Decrypt(const std::string& ciphertext, std::string* plaintext);
 
+  // Update the counter value when in CTR mode. Currently only 128-bits
+  // counter value is supported.

[wtc, 2011/06/21 00:33:32]

Nit: remove "Currently only 128-bits counter value is supported."

This is documented above in front of the Counter class.

+  //
+  // Return true only if update was successful.

[wtc, 2011/06/21 00:33:32]

Nit: the Style guide recommends using "descriptive" rather
than "imperative" verbs, so use "Updates", "Returns",
"Generates", and "Masks" instead of "Update", "Return",
"Generate", and "Mask".

http://google-styleguide.googlecode.com/svn/trunk/cppguide.xml#Function_Comments

Nit: should this method be named SetCounter()?
"UpdateCounter" seems to imply it increments the counter.

+  bool UpdateCounter(const std::string& counter);
+
   // TODO(albertb): Support streaming encryption.
 
  private:
+  // Generate a mask using |counter_| to be used for encryption in CTR mode.
+  // Resulting mask will be written to |mask| with |mask_len| bytes.
+  //
+  // The generated mask will always have at least |plaintext_len| bytes and
+  // will be a multiple of the counter length.
+  //
+  // This method is used only in CTR mode.
+  void GenerateCounterMask(size_t plaintext_len,
+                           scoped_array<uint8>* mask,
+                           size_t* mask_len);
+
+  // Mask the |plaintext| message using |mask|. The output will be written to
+  // |ciphertext|. |ciphertext| must have at least |plaintext_len| bytes.
+  void MaskMessage(const void* plaintext,
+                   size_t plaintext_len,
+                   const void* mask,
+                   void* ciphertext) const;
+
   SymmetricKey* key_;
   Mode mode_;
+  scoped_ptr<Counter> counter_;
 
 #if defined(USE_OPENSSL)
   bool Crypt(bool encrypt,  // Pass true to encrypt, false to decrypt.
              const std::string& input,
              std::string* output);
   std::string iv_;
 #elif defined(USE_NSS)
+  bool Crypt(PK11Context* context,
+             const std::string& input,
+             std::string* output);
+  bool CryptCTR(PK11Context* context,
+                const std::string& input,
+                std::string* output);
   ScopedPK11Slot slot_;
   ScopedSECItem param_;
 #elif defined(OS_MACOSX)
   bool Crypt(int /*CCOperation*/ op,
              const std::string& input,
              std::string* output);
 
   std::string iv_;
 #elif defined(OS_WIN)
   ScopedHCRYPTKEY capi_key_;
   DWORD block_size_;
 #endif
 };
 
 }  // namespace crypto
 
 #endif  // CRYPTO_ENCRYPTOR_H_